Contact Dermatitis

Nasal tanning spray is a recent phenomenon that has been gaining popularity among consumers on TikTok and other social media platforms. The active ingredient in the tanning spray is melanotan II—a synthetic analog of α‒melanocyte-stimulating hormone,^1,2 a naturally occurring hormone responsible for skin pigmentation. α‒Melanocyte-stimulating hormone is a derivative of the precursor proopiomelanocortin, an agonist on the melanocortin-1 receptor that promotes formation of eumelanin.^1,3 Eumelanin then provides pigmentation to the skin.³ Apart from its use for tanning, melanotan II has been reported to increase sexual function and aid in weight loss.¹

Melanotan II is not approved by the US Food and Drug Administration; however, injectable formulations can be obtained illegally on the Internet as well as at some tanning salons and beauty parlors.⁴ Although injectable forms of melanotan II have been used for years to artificially increase skin pigmentation, the newly hyped nasal tanning sprays are drawing the attention of consumers. The synthetic chemical spray is inhaled into the nasal mucosae, where it is readily absorbed into the bloodstream to act on melanocortin receptors throughout the body, thus enhancing skin pigmentation.² Because melanotan II is not approved, there is no guarantee that the product purchased from those sources is pure; therefore, consumers risk inhaling or injecting contaminated chemicals.⁵

In a 2017 study, Kirk and Greenfield⁶ cited self-image as a common concern among participants who expressed a preference for appearing tanned.⁶ Societal influence and standards to which young adults, particularly young women, often are accustomed drive some to take steps to achieve tanned skin, which they view as more attractive and healthier than untanned skin.^7,8

Social media consumption is a significant risk factor for developing or exacerbating body dissatisfaction among impressionable teenagers and young adults, who may be less risk averse and therefore choose to embrace trends such as nasal tanning sprays to enhance their appearance, without considering possible consequences. Most young adults, and even teens, are aware of the risks associated with tanning beds, which may propel them to seek out what they perceive as a less-risky tanning alternative such as a tanner delivered via a nasal route, but it is unlikely that this group is fully informed about the possible dangers of nasal tanning sprays.

It is crucial for dermatologists and other clinicians to provide awareness and education about the potential harm of nasal tanning sprays. Along with the general risks of using an unregulated substance, common adverse effects include acne, facial flushing, gastrointestinal tract upset, and sensitivity to sunlight (Table).^1,9,10 Several case reports have linked melanotan II to cutaneous changes, including dysplastic nevi and even melanoma.¹ Less common complications, such as renal infarction and priapism, also have been observed with melanotan II use.^9,10

Even with the known risks involving tanning beds and skin cancer, an analysis by Kream et al¹¹ in 2020 showed that 90% (441/488) of tanning-related videos on TikTok promoted a positive view of tanning. Of these TikTok videos involving pro-tanning trends, 3% (12/441) were specifically about melanotan II nasal spray, injection, or both, which has only become more popular since this study was published.¹¹

Dermatologists should be aware of the impact that tanning trends, such as nasal tanning spray, can have on all patients and initiate discussions regarding the risks of using these products with patients as appropriate. Alternatives to nasal tanning sprays such as spray-on tans and self-tanning lotions are safer ways for patients to achieve a tanned look without the health risks associated with melanotan II.

Nasal tanning spray is a recent phenomenon that has been gaining popularity among consumers on TikTok and other social media platforms. The active ingredient in the tanning spray is melanotan II—a synthetic analog of α‒melanocyte-stimulating hormone,^1,2 a naturally occurring hormone responsible for skin pigmentation. α‒Melanocyte-stimulating hormone is a derivative of the precursor proopiomelanocortin, an agonist on the melanocortin-1 receptor that promotes formation of eumelanin.^1,3 Eumelanin then provides pigmentation to the skin.³ Apart from its use for tanning, melanotan II has been reported to increase sexual function and aid in weight loss.¹

Melanotan II is not approved by the US Food and Drug Administration; however, injectable formulations can be obtained illegally on the Internet as well as at some tanning salons and beauty parlors.⁴ Although injectable forms of melanotan II have been used for years to artificially increase skin pigmentation, the newly hyped nasal tanning sprays are drawing the attention of consumers. The synthetic chemical spray is inhaled into the nasal mucosae, where it is readily absorbed into the bloodstream to act on melanocortin receptors throughout the body, thus enhancing skin pigmentation.² Because melanotan II is not approved, there is no guarantee that the product purchased from those sources is pure; therefore, consumers risk inhaling or injecting contaminated chemicals.⁵

In a 2017 study, Kirk and Greenfield⁶ cited self-image as a common concern among participants who expressed a preference for appearing tanned.⁶ Societal influence and standards to which young adults, particularly young women, often are accustomed drive some to take steps to achieve tanned skin, which they view as more attractive and healthier than untanned skin.^7,8

Social media consumption is a significant risk factor for developing or exacerbating body dissatisfaction among impressionable teenagers and young adults, who may be less risk averse and therefore choose to embrace trends such as nasal tanning sprays to enhance their appearance, without considering possible consequences. Most young adults, and even teens, are aware of the risks associated with tanning beds, which may propel them to seek out what they perceive as a less-risky tanning alternative such as a tanner delivered via a nasal route, but it is unlikely that this group is fully informed about the possible dangers of nasal tanning sprays.

It is crucial for dermatologists and other clinicians to provide awareness and education about the potential harm of nasal tanning sprays. Along with the general risks of using an unregulated substance, common adverse effects include acne, facial flushing, gastrointestinal tract upset, and sensitivity to sunlight (Table).^1,9,10 Several case reports have linked melanotan II to cutaneous changes, including dysplastic nevi and even melanoma.¹ Less common complications, such as renal infarction and priapism, also have been observed with melanotan II use.^9,10

Even with the known risks involving tanning beds and skin cancer, an analysis by Kream et al¹¹ in 2020 showed that 90% (441/488) of tanning-related videos on TikTok promoted a positive view of tanning. Of these TikTok videos involving pro-tanning trends, 3% (12/441) were specifically about melanotan II nasal spray, injection, or both, which has only become more popular since this study was published.¹¹

Dermatologists should be aware of the impact that tanning trends, such as nasal tanning spray, can have on all patients and initiate discussions regarding the risks of using these products with patients as appropriate. Alternatives to nasal tanning sprays such as spray-on tans and self-tanning lotions are safer ways for patients to achieve a tanned look without the health risks associated with melanotan II.

Nasal tanning spray is a recent phenomenon that has been gaining popularity among consumers on TikTok and other social media platforms. The active ingredient in the tanning spray is melanotan II—a synthetic analog of α‒melanocyte-stimulating hormone,^1,2 a naturally occurring hormone responsible for skin pigmentation. α‒Melanocyte-stimulating hormone is a derivative of the precursor proopiomelanocortin, an agonist on the melanocortin-1 receptor that promotes formation of eumelanin.^1,3 Eumelanin then provides pigmentation to the skin.³ Apart from its use for tanning, melanotan II has been reported to increase sexual function and aid in weight loss.¹

Melanotan II is not approved by the US Food and Drug Administration; however, injectable formulations can be obtained illegally on the Internet as well as at some tanning salons and beauty parlors.⁴ Although injectable forms of melanotan II have been used for years to artificially increase skin pigmentation, the newly hyped nasal tanning sprays are drawing the attention of consumers. The synthetic chemical spray is inhaled into the nasal mucosae, where it is readily absorbed into the bloodstream to act on melanocortin receptors throughout the body, thus enhancing skin pigmentation.² Because melanotan II is not approved, there is no guarantee that the product purchased from those sources is pure; therefore, consumers risk inhaling or injecting contaminated chemicals.⁵

In a 2017 study, Kirk and Greenfield⁶ cited self-image as a common concern among participants who expressed a preference for appearing tanned.⁶ Societal influence and standards to which young adults, particularly young women, often are accustomed drive some to take steps to achieve tanned skin, which they view as more attractive and healthier than untanned skin.^7,8

Social media consumption is a significant risk factor for developing or exacerbating body dissatisfaction among impressionable teenagers and young adults, who may be less risk averse and therefore choose to embrace trends such as nasal tanning sprays to enhance their appearance, without considering possible consequences. Most young adults, and even teens, are aware of the risks associated with tanning beds, which may propel them to seek out what they perceive as a less-risky tanning alternative such as a tanner delivered via a nasal route, but it is unlikely that this group is fully informed about the possible dangers of nasal tanning sprays.

It is crucial for dermatologists and other clinicians to provide awareness and education about the potential harm of nasal tanning sprays. Along with the general risks of using an unregulated substance, common adverse effects include acne, facial flushing, gastrointestinal tract upset, and sensitivity to sunlight (Table).^1,9,10 Several case reports have linked melanotan II to cutaneous changes, including dysplastic nevi and even melanoma.¹ Less common complications, such as renal infarction and priapism, also have been observed with melanotan II use.^9,10

Even with the known risks involving tanning beds and skin cancer, an analysis by Kream et al¹¹ in 2020 showed that 90% (441/488) of tanning-related videos on TikTok promoted a positive view of tanning. Of these TikTok videos involving pro-tanning trends, 3% (12/441) were specifically about melanotan II nasal spray, injection, or both, which has only become more popular since this study was published.¹¹

Dermatologists should be aware of the impact that tanning trends, such as nasal tanning spray, can have on all patients and initiate discussions regarding the risks of using these products with patients as appropriate. Alternatives to nasal tanning sprays such as spray-on tans and self-tanning lotions are safer ways for patients to achieve a tanned look without the health risks associated with melanotan II.

Acrylates are a ubiquitous family of synthetic thermoplastic resins that are employed in a wide array of products. Since the discovery of acrylic acid in 1843 and its industrialization in the early 20th century, acrylates have been used by many different sectors of industry.¹ Today, acrylates can be found in diverse sources such as adhesives, coatings, electronics, nail cosmetics, dental materials, and medical devices. Although these versatile compounds have revolutionized numerous sectors, their potential to trigger allergic contact dermatitis (ACD) has garnered considerable attention in recent years. In 2012, acrylates as a group were named Allergen of the Year by the American Contact Dermatitis Society,² and one member—isobornyl acrylate—also was given the infamous award in 2020.³ In this article, we highlight the chemistry of acrylates, the growing prevalence of acrylate contact allergy, common sources of exposure, patch testing considerations, and management/prevention strategies.

Chemistry and Uses of Acrylates

Acrylates are widely used due to their pliable and resilient properties.⁴ They begin as liquid monomers of (meth)acrylic acid or cyanoacrylic acid that are molded to the desired application before being cured or hardened by one of several means: spontaneously, using chemical catalysts, or with heat, UV light, or a light-emitting diode. Once cured, the final polymers (ie, [meth]acrylates, cyanoacrylates) serve a myriad of different purposes. Table 1 includes some of the more clinically relevant sources of acrylate exposure. Although this list is not comprehensive, it offers a glimpse into the vast array of uses for acrylates.

Acrylate Contact Allergy

Acrylic monomers are potent contact allergens, but the polymerized final products are not considered allergenic, assuming they are completely cured; however, ACD can occur with incomplete curing.⁶ It is of clinical importance that once an individual becomes sensitized to one type of acrylate, they may develop cross-reactions to others contained in different products. Notably, cyanoacrylates generally do not cross-react with (meth)acrylates; this has important implications for choosing safe alternative products in sensitized patients, though independent sensitization to cyanoacrylates is possible.^7,8

Epidemiology and Risk Factors

The prevalence of acrylate allergy in the general population is unknown; however, there is a trend of increased patch test positivity in studies of patients referred for patch testing. A 2018 study by the European Environmental Contact Dermatitis Research Group reported positive patch tests to acrylates in 1.1% of 18,228 patients tested from 2013 to 2015.⁹ More recently, a multicenter European study (2019-2020) reported a 2.3% patch test positivity to 2-hydroxyethyl methacrylate (HEMA) among 7675 tested individuals,¹⁰ and even higher HEMA positivity was reported in Spain (3.7% of 1884 patients in 2019-2020).¹¹ In addition, the North American Contact Dermatitis Group (NACDG) reported positive patch test reactions to HEMA in 3.2% of 4111 patients tested from 2019 to 2020, a statistically significant increase compared with those tested in 2009 to 2018 (odds ratio, 1.25 [95% CI, 1.03-1.51]; P=.02).¹²

Historically, acrylate sensitization primarily stemmed from occupational exposure. A retrospective analysis of occupational dermatitis performed by the NACDG (2001-2016) showed that HEMA was among the top 10 most common occupational allergens (3.4% positivity [83/2461]) and had the fifth highest percentage of occupationally relevant reactions (73.5% [83/113]).¹³ High-risk occupations include dental providers and nail technicians. Dentistry utilizes many materials containing acrylates, including uncured plastic resins used in dental prostheses, dentin bonding materials, and glass ionomers.¹⁴ A retrospective analysis of 585 dental personnel who were patch tested by the NACDG (2001-2018) found that more than 20% of occupational ACD cases were related to acrylates.¹⁵ Nail technicians are another group routinely exposed to acrylates through a variety of modern nail cosmetics. In a 7-year study from Portugal evaluating acrylate ACD, 68% (25/37) of cases were attributed to occupation, 80% (20/25) of which were in nail technicians.¹⁶ Likewise, among 28 nail technicians in Sweden who were referred for patch testing, 57% (16/28) tested positive for at least 1 acrylate.¹⁷

Modern Sources of Acrylate Exposure

Once thought to be a predominantly occupational exposure, acrylates have rapidly made their way into everyday consumer products. Clinicians should be aware of several sources of clinically relevant acrylate exposure, including nail cosmetics, consumer electronics, and medical/surgical adhesives.

A 2016 study found a shift to nail cosmetics as the most common source of acrylate sensitization.¹⁸ Nail cosmetics that contain acrylates include traditional acrylic, gel (shellac), dipped, and press-on (false) nails.¹⁹ The NACDG found that the most common allergen in patients experiencing ACD associated with nail products (2001-2016) was HEMA (56.6% [273/482]), far ahead of the traditional nail polish allergen tosylamide (36.2% [273/755]). Over the study period, the frequency of positive patch tests statistically increased for HEMA (P=.0069) and decreased for tosylamide (P<.0001).²⁰ There is concern that the use of home gel nail kits, which can be purchased online at the click of a button, may be associated with a risk for acrylate sensitization.^21,22 A recent study surveyed a Facebook support group for individuals with self-reported reactions to nail cosmetics, finding that 78% of the 199 individuals had used at-home gel nail kits, and more than 80% of them first developed skin reactions after starting to use at-home kits.²³ The risks for sensitization are thought to be greater when self-applying nail acrylates compared to having them done professionally because individuals are more likely to spill allergenic monomers onto the skin at home; it also is possible that home techniques could lead to incomplete curing. Table 2 reviews the different types of acrylic nail cosmetics.

Medical adhesives and equipment are other important areas where acrylates can be encountered in abundance. A review by Spencer et al¹⁸ cautioned wound dressings as an up-and-coming source of sensitization, and this has been demonstrated in the literature as coming to fruition.²⁶ Another study identified acrylates in 15 of 16 (94%) tested medical adhesives; among 7 medical adhesives labeled as hypoallergenic, 100% still contained acrylates and/or abietic acid.²⁷ Multiple case reports have described ACD to adhesives of electrocardiogram electrodes containing acrylates.^28-31 Physicians providing care to patients with diabetes mellitus also must be aware of acrylates in glucose monitors and insulin pumps, either found in the adhesives or leaching from the inside of the device to reach the skin.³² Isobornyl acrylate in particular has made quite the name for itself in this sector, being crowned the 2020 Allergen of the Year owing to its key role in cases of ACD to diabetes devices.³

Cyanoacrylate-based tissue adhesives (eg, 2‐octyl cyanoacrylate) are now well documented to cause postoperative ACD.^33,34 Although robust prospective data are limited, studies suggest that 2% to 14% of patients develop postoperative skin reactions following 2-octyl cyanoacrylate application.^35-37 It has been shown that sensitization to tissue adhesives often occurs after the first application, followed by an eruption of ACD as long as a month later, which can create confusion about the nature of the rash for patients and health care providers alike, who may for instance attribute it to infection rather than allergy.³⁸ In the orthopedic literature, a woman with a known history of acrylic nail ACD had knee arthroplasty failure attributed to acrylic bone cement with resolution of the joint symptoms after changing to a cementless device.³⁹

Awareness of the common use of acrylates is important to identify the cause of reactions from products that would otherwise seem nonallergenic. A case of occupational ACD to isobornyl acrylate in UV-cured phone screen protectors has been reported⁴⁰; several cases of ACD to acrylates in headphones^41,42 as well as one related to a wearable fitness device also have been reported.⁴³ Given all these possible sources of exposure, ACD to acrylates should be on your radar.

When to Consider Acrylate ACD

When working up a patient with dermatitis, it is essential to ask about occupational history and hobbies to get a sense of potential contact allergen exposures. The typical presentation of occupational acrylate-associated ACD is hand eczema, specifically involving the fingertips.^5,24,25,44 Acrylate ACD should be considered in patients with nail dystrophy and a history of wearing acrylic nails.⁴⁵ There can even be involvement of the face and eyelids secondary to airborne contact or ectopic spread from the hands.²⁴ Spreading vesicular eruptions associated with adhesives also should raise concern. The Figure depicts several possible presentations of ACD to acrylates. In a time of abundant access to products containing acrylates, dermatologists should consider this allergy in their differential diagnosis and consider patch testing.

Photographs courtesy of Brandon L. Adler, MD.

Patch Testing to Acrylates

The gold standard for ACD diagnosis is patch testing. It should be noted that no acrylates are included in the thin-layer rapid use epicutaneous (T.R.U.E.) test series. Several acrylates are tested in expanded patch test series including the American Contact Dermatitis Society Core Allergen series and North American 80 Comprehensive Series. 2-Hydroxyethyl methacrylate is thought to be the most important screening allergen to test. Ramos et al¹⁶ reported a positive patch test to HEMA in 81% (30/37) of patients who had any type of acrylate allergy.

If initial testing to a limited number of acrylates is negative but clinical suspicion remains high, expanded acrylates/plastics and glue series also are available from commercial patch test suppliers. Testing to an expanded panel of acrylates is especially pertinent to consider in suspected occupational cases given the risk of workplace absenteeism and even disability that come with continued exposure to the allergen. Of note, isobornyl acrylate is not included in the baseline patch test series and must be tested separately, particularly because it usually does not cross-react with other acrylates, and therefore allergy could be missed if not tested on its own.

Acrylates are volatile substances that have been shown to degrade at room temperature and to a lesser degree when refrigerated. Ideally, they should be stored in a freezer and not used beyond their expiration date. Furthermore, it is advised that acrylate patch tests be prepared immediately prior to placement on the patient and to discard the initial extrusion from the syringe, as the concentration at the tip may be decreased.^46,47

With regard to tissue adhesives, the actual product should be tested as-is because these are not commercially available patch test substances.⁴⁸ Occasionally, patients who are sensitized to the tissue adhesive will not react when patch tested on intact skin. If clinical suspicion remains high, scratch patch testing may confirm contact allergy in cases of negative testing on intact skin.⁴⁹

Management and Prevention

Once a diagnosis of ACD secondary to acrylates has been established, counseling patients on allergen avoidance strategies is essential. For (meth)acrylate-allergic patients who want to continue using modern nail products, cyanoacrylate-based options (eg, dipped, press-on nails) can be considered as an alternative, as they do not cross-react, though independent sensitization is still possible. However, traditional nail polish is the safest option to recommend.

The concern with acrylate sensitization extends beyond the immediate issue that brought the patient into your clinic. Dermatologists must counsel patients who are sensitized to acrylates on the possible sequelae of acrylate-containing dental or orthopedic procedures. Oral lichenoid lesions, denture stomatitis, burning mouth syndrome, or even acute facial swelling have been reported following dental work in patients with acrylate allergy.^50-53 Dentists of patients with acrylate ACD should be informed of the diagnosis so acrylates can be avoided during dental work; if unavoidable, all possible steps should be taken to ensure complete curing of the monomers. In the surgical setting, patients sensitized to cyanoacrylate-based tissue adhesives should be offered wound closure alternatives such as sutures or staples.³⁴

In patients with diabetes mellitus who develop ACD to their glucose monitor or insulin pump, ideally they should be switched to a device that does not contain acrylates. Problematically, these devices are constantly being reformulated, and manufacturers do not always divulge their components, which can make it challenging to determine safe alternative options.^32,54 Various barrier products may help on a case-by-case basis.⁵⁵Preventative measures should be implemented in workplaces that utilize acrylates, including dental practices and nail salons. Acrylic monomers have been shown to penetrate most gloves within minutes of exposure.^56,57 Double gloving with nitrile gloves affords some protection for no longer than 60 minutes.⁶ 4H gloves have been shown to provide true protection but result in a loss of dexterity.⁵⁸ The fingerstall technique involves removing the fingers from a 4H glove, inserting them on the fingers, and applying a more flexible glove on top to hold them in place; this offers a hybrid between protection and finger dexterity.⁵⁹

Final Interpretation

In a world characterized by technological advancements and increasing accessibility to acrylate-containing products, we hope this brief review serves as a resource and reminder to dermatologists to consider acrylates as a potential cause of ACD with diverse presentations and important future implications for affected individuals. The rising trend of acrylate allergy necessitates comprehensive assessment and shared decision-making between physicians and patients. As we navigate the ever-changing landscape of materials and technologies, clinicians must remain vigilant to avoid some potentially sticky situations for patients.

Acrylates are a ubiquitous family of synthetic thermoplastic resins that are employed in a wide array of products. Since the discovery of acrylic acid in 1843 and its industrialization in the early 20th century, acrylates have been used by many different sectors of industry.¹ Today, acrylates can be found in diverse sources such as adhesives, coatings, electronics, nail cosmetics, dental materials, and medical devices. Although these versatile compounds have revolutionized numerous sectors, their potential to trigger allergic contact dermatitis (ACD) has garnered considerable attention in recent years. In 2012, acrylates as a group were named Allergen of the Year by the American Contact Dermatitis Society,² and one member—isobornyl acrylate—also was given the infamous award in 2020.³ In this article, we highlight the chemistry of acrylates, the growing prevalence of acrylate contact allergy, common sources of exposure, patch testing considerations, and management/prevention strategies.

Chemistry and Uses of Acrylates

Acrylates are widely used due to their pliable and resilient properties.⁴ They begin as liquid monomers of (meth)acrylic acid or cyanoacrylic acid that are molded to the desired application before being cured or hardened by one of several means: spontaneously, using chemical catalysts, or with heat, UV light, or a light-emitting diode. Once cured, the final polymers (ie, [meth]acrylates, cyanoacrylates) serve a myriad of different purposes. Table 1 includes some of the more clinically relevant sources of acrylate exposure. Although this list is not comprehensive, it offers a glimpse into the vast array of uses for acrylates.

Acrylate Contact Allergy

Acrylic monomers are potent contact allergens, but the polymerized final products are not considered allergenic, assuming they are completely cured; however, ACD can occur with incomplete curing.⁶ It is of clinical importance that once an individual becomes sensitized to one type of acrylate, they may develop cross-reactions to others contained in different products. Notably, cyanoacrylates generally do not cross-react with (meth)acrylates; this has important implications for choosing safe alternative products in sensitized patients, though independent sensitization to cyanoacrylates is possible.^7,8

Epidemiology and Risk Factors

The prevalence of acrylate allergy in the general population is unknown; however, there is a trend of increased patch test positivity in studies of patients referred for patch testing. A 2018 study by the European Environmental Contact Dermatitis Research Group reported positive patch tests to acrylates in 1.1% of 18,228 patients tested from 2013 to 2015.⁹ More recently, a multicenter European study (2019-2020) reported a 2.3% patch test positivity to 2-hydroxyethyl methacrylate (HEMA) among 7675 tested individuals,¹⁰ and even higher HEMA positivity was reported in Spain (3.7% of 1884 patients in 2019-2020).¹¹ In addition, the North American Contact Dermatitis Group (NACDG) reported positive patch test reactions to HEMA in 3.2% of 4111 patients tested from 2019 to 2020, a statistically significant increase compared with those tested in 2009 to 2018 (odds ratio, 1.25 [95% CI, 1.03-1.51]; P=.02).¹²

Historically, acrylate sensitization primarily stemmed from occupational exposure. A retrospective analysis of occupational dermatitis performed by the NACDG (2001-2016) showed that HEMA was among the top 10 most common occupational allergens (3.4% positivity [83/2461]) and had the fifth highest percentage of occupationally relevant reactions (73.5% [83/113]).¹³ High-risk occupations include dental providers and nail technicians. Dentistry utilizes many materials containing acrylates, including uncured plastic resins used in dental prostheses, dentin bonding materials, and glass ionomers.¹⁴ A retrospective analysis of 585 dental personnel who were patch tested by the NACDG (2001-2018) found that more than 20% of occupational ACD cases were related to acrylates.¹⁵ Nail technicians are another group routinely exposed to acrylates through a variety of modern nail cosmetics. In a 7-year study from Portugal evaluating acrylate ACD, 68% (25/37) of cases were attributed to occupation, 80% (20/25) of which were in nail technicians.¹⁶ Likewise, among 28 nail technicians in Sweden who were referred for patch testing, 57% (16/28) tested positive for at least 1 acrylate.¹⁷

Modern Sources of Acrylate Exposure

Once thought to be a predominantly occupational exposure, acrylates have rapidly made their way into everyday consumer products. Clinicians should be aware of several sources of clinically relevant acrylate exposure, including nail cosmetics, consumer electronics, and medical/surgical adhesives.

A 2016 study found a shift to nail cosmetics as the most common source of acrylate sensitization.¹⁸ Nail cosmetics that contain acrylates include traditional acrylic, gel (shellac), dipped, and press-on (false) nails.¹⁹ The NACDG found that the most common allergen in patients experiencing ACD associated with nail products (2001-2016) was HEMA (56.6% [273/482]), far ahead of the traditional nail polish allergen tosylamide (36.2% [273/755]). Over the study period, the frequency of positive patch tests statistically increased for HEMA (P=.0069) and decreased for tosylamide (P<.0001).²⁰ There is concern that the use of home gel nail kits, which can be purchased online at the click of a button, may be associated with a risk for acrylate sensitization.^21,22 A recent study surveyed a Facebook support group for individuals with self-reported reactions to nail cosmetics, finding that 78% of the 199 individuals had used at-home gel nail kits, and more than 80% of them first developed skin reactions after starting to use at-home kits.²³ The risks for sensitization are thought to be greater when self-applying nail acrylates compared to having them done professionally because individuals are more likely to spill allergenic monomers onto the skin at home; it also is possible that home techniques could lead to incomplete curing. Table 2 reviews the different types of acrylic nail cosmetics.

Medical adhesives and equipment are other important areas where acrylates can be encountered in abundance. A review by Spencer et al¹⁸ cautioned wound dressings as an up-and-coming source of sensitization, and this has been demonstrated in the literature as coming to fruition.²⁶ Another study identified acrylates in 15 of 16 (94%) tested medical adhesives; among 7 medical adhesives labeled as hypoallergenic, 100% still contained acrylates and/or abietic acid.²⁷ Multiple case reports have described ACD to adhesives of electrocardiogram electrodes containing acrylates.^28-31 Physicians providing care to patients with diabetes mellitus also must be aware of acrylates in glucose monitors and insulin pumps, either found in the adhesives or leaching from the inside of the device to reach the skin.³² Isobornyl acrylate in particular has made quite the name for itself in this sector, being crowned the 2020 Allergen of the Year owing to its key role in cases of ACD to diabetes devices.³

Cyanoacrylate-based tissue adhesives (eg, 2‐octyl cyanoacrylate) are now well documented to cause postoperative ACD.^33,34 Although robust prospective data are limited, studies suggest that 2% to 14% of patients develop postoperative skin reactions following 2-octyl cyanoacrylate application.^35-37 It has been shown that sensitization to tissue adhesives often occurs after the first application, followed by an eruption of ACD as long as a month later, which can create confusion about the nature of the rash for patients and health care providers alike, who may for instance attribute it to infection rather than allergy.³⁸ In the orthopedic literature, a woman with a known history of acrylic nail ACD had knee arthroplasty failure attributed to acrylic bone cement with resolution of the joint symptoms after changing to a cementless device.³⁹

Awareness of the common use of acrylates is important to identify the cause of reactions from products that would otherwise seem nonallergenic. A case of occupational ACD to isobornyl acrylate in UV-cured phone screen protectors has been reported⁴⁰; several cases of ACD to acrylates in headphones^41,42 as well as one related to a wearable fitness device also have been reported.⁴³ Given all these possible sources of exposure, ACD to acrylates should be on your radar.

When to Consider Acrylate ACD

When working up a patient with dermatitis, it is essential to ask about occupational history and hobbies to get a sense of potential contact allergen exposures. The typical presentation of occupational acrylate-associated ACD is hand eczema, specifically involving the fingertips.^5,24,25,44 Acrylate ACD should be considered in patients with nail dystrophy and a history of wearing acrylic nails.⁴⁵ There can even be involvement of the face and eyelids secondary to airborne contact or ectopic spread from the hands.²⁴ Spreading vesicular eruptions associated with adhesives also should raise concern. The Figure depicts several possible presentations of ACD to acrylates. In a time of abundant access to products containing acrylates, dermatologists should consider this allergy in their differential diagnosis and consider patch testing.

Photographs courtesy of Brandon L. Adler, MD.

Patch Testing to Acrylates

The gold standard for ACD diagnosis is patch testing. It should be noted that no acrylates are included in the thin-layer rapid use epicutaneous (T.R.U.E.) test series. Several acrylates are tested in expanded patch test series including the American Contact Dermatitis Society Core Allergen series and North American 80 Comprehensive Series. 2-Hydroxyethyl methacrylate is thought to be the most important screening allergen to test. Ramos et al¹⁶ reported a positive patch test to HEMA in 81% (30/37) of patients who had any type of acrylate allergy.

If initial testing to a limited number of acrylates is negative but clinical suspicion remains high, expanded acrylates/plastics and glue series also are available from commercial patch test suppliers. Testing to an expanded panel of acrylates is especially pertinent to consider in suspected occupational cases given the risk of workplace absenteeism and even disability that come with continued exposure to the allergen. Of note, isobornyl acrylate is not included in the baseline patch test series and must be tested separately, particularly because it usually does not cross-react with other acrylates, and therefore allergy could be missed if not tested on its own.

Acrylates are volatile substances that have been shown to degrade at room temperature and to a lesser degree when refrigerated. Ideally, they should be stored in a freezer and not used beyond their expiration date. Furthermore, it is advised that acrylate patch tests be prepared immediately prior to placement on the patient and to discard the initial extrusion from the syringe, as the concentration at the tip may be decreased.^46,47

With regard to tissue adhesives, the actual product should be tested as-is because these are not commercially available patch test substances.⁴⁸ Occasionally, patients who are sensitized to the tissue adhesive will not react when patch tested on intact skin. If clinical suspicion remains high, scratch patch testing may confirm contact allergy in cases of negative testing on intact skin.⁴⁹

Management and Prevention

Once a diagnosis of ACD secondary to acrylates has been established, counseling patients on allergen avoidance strategies is essential. For (meth)acrylate-allergic patients who want to continue using modern nail products, cyanoacrylate-based options (eg, dipped, press-on nails) can be considered as an alternative, as they do not cross-react, though independent sensitization is still possible. However, traditional nail polish is the safest option to recommend.

The concern with acrylate sensitization extends beyond the immediate issue that brought the patient into your clinic. Dermatologists must counsel patients who are sensitized to acrylates on the possible sequelae of acrylate-containing dental or orthopedic procedures. Oral lichenoid lesions, denture stomatitis, burning mouth syndrome, or even acute facial swelling have been reported following dental work in patients with acrylate allergy.^50-53 Dentists of patients with acrylate ACD should be informed of the diagnosis so acrylates can be avoided during dental work; if unavoidable, all possible steps should be taken to ensure complete curing of the monomers. In the surgical setting, patients sensitized to cyanoacrylate-based tissue adhesives should be offered wound closure alternatives such as sutures or staples.³⁴

In patients with diabetes mellitus who develop ACD to their glucose monitor or insulin pump, ideally they should be switched to a device that does not contain acrylates. Problematically, these devices are constantly being reformulated, and manufacturers do not always divulge their components, which can make it challenging to determine safe alternative options.^32,54 Various barrier products may help on a case-by-case basis.⁵⁵Preventative measures should be implemented in workplaces that utilize acrylates, including dental practices and nail salons. Acrylic monomers have been shown to penetrate most gloves within minutes of exposure.^56,57 Double gloving with nitrile gloves affords some protection for no longer than 60 minutes.⁶ 4H gloves have been shown to provide true protection but result in a loss of dexterity.⁵⁸ The fingerstall technique involves removing the fingers from a 4H glove, inserting them on the fingers, and applying a more flexible glove on top to hold them in place; this offers a hybrid between protection and finger dexterity.⁵⁹

Final Interpretation

In a world characterized by technological advancements and increasing accessibility to acrylate-containing products, we hope this brief review serves as a resource and reminder to dermatologists to consider acrylates as a potential cause of ACD with diverse presentations and important future implications for affected individuals. The rising trend of acrylate allergy necessitates comprehensive assessment and shared decision-making between physicians and patients. As we navigate the ever-changing landscape of materials and technologies, clinicians must remain vigilant to avoid some potentially sticky situations for patients.

Acrylates are a ubiquitous family of synthetic thermoplastic resins that are employed in a wide array of products. Since the discovery of acrylic acid in 1843 and its industrialization in the early 20th century, acrylates have been used by many different sectors of industry.¹ Today, acrylates can be found in diverse sources such as adhesives, coatings, electronics, nail cosmetics, dental materials, and medical devices. Although these versatile compounds have revolutionized numerous sectors, their potential to trigger allergic contact dermatitis (ACD) has garnered considerable attention in recent years. In 2012, acrylates as a group were named Allergen of the Year by the American Contact Dermatitis Society,² and one member—isobornyl acrylate—also was given the infamous award in 2020.³ In this article, we highlight the chemistry of acrylates, the growing prevalence of acrylate contact allergy, common sources of exposure, patch testing considerations, and management/prevention strategies.

Chemistry and Uses of Acrylates

Acrylates are widely used due to their pliable and resilient properties.⁴ They begin as liquid monomers of (meth)acrylic acid or cyanoacrylic acid that are molded to the desired application before being cured or hardened by one of several means: spontaneously, using chemical catalysts, or with heat, UV light, or a light-emitting diode. Once cured, the final polymers (ie, [meth]acrylates, cyanoacrylates) serve a myriad of different purposes. Table 1 includes some of the more clinically relevant sources of acrylate exposure. Although this list is not comprehensive, it offers a glimpse into the vast array of uses for acrylates.

Acrylate Contact Allergy

Acrylic monomers are potent contact allergens, but the polymerized final products are not considered allergenic, assuming they are completely cured; however, ACD can occur with incomplete curing.⁶ It is of clinical importance that once an individual becomes sensitized to one type of acrylate, they may develop cross-reactions to others contained in different products. Notably, cyanoacrylates generally do not cross-react with (meth)acrylates; this has important implications for choosing safe alternative products in sensitized patients, though independent sensitization to cyanoacrylates is possible.^7,8

Epidemiology and Risk Factors

The prevalence of acrylate allergy in the general population is unknown; however, there is a trend of increased patch test positivity in studies of patients referred for patch testing. A 2018 study by the European Environmental Contact Dermatitis Research Group reported positive patch tests to acrylates in 1.1% of 18,228 patients tested from 2013 to 2015.⁹ More recently, a multicenter European study (2019-2020) reported a 2.3% patch test positivity to 2-hydroxyethyl methacrylate (HEMA) among 7675 tested individuals,¹⁰ and even higher HEMA positivity was reported in Spain (3.7% of 1884 patients in 2019-2020).¹¹ In addition, the North American Contact Dermatitis Group (NACDG) reported positive patch test reactions to HEMA in 3.2% of 4111 patients tested from 2019 to 2020, a statistically significant increase compared with those tested in 2009 to 2018 (odds ratio, 1.25 [95% CI, 1.03-1.51]; P=.02).¹²

Historically, acrylate sensitization primarily stemmed from occupational exposure. A retrospective analysis of occupational dermatitis performed by the NACDG (2001-2016) showed that HEMA was among the top 10 most common occupational allergens (3.4% positivity [83/2461]) and had the fifth highest percentage of occupationally relevant reactions (73.5% [83/113]).¹³ High-risk occupations include dental providers and nail technicians. Dentistry utilizes many materials containing acrylates, including uncured plastic resins used in dental prostheses, dentin bonding materials, and glass ionomers.¹⁴ A retrospective analysis of 585 dental personnel who were patch tested by the NACDG (2001-2018) found that more than 20% of occupational ACD cases were related to acrylates.¹⁵ Nail technicians are another group routinely exposed to acrylates through a variety of modern nail cosmetics. In a 7-year study from Portugal evaluating acrylate ACD, 68% (25/37) of cases were attributed to occupation, 80% (20/25) of which were in nail technicians.¹⁶ Likewise, among 28 nail technicians in Sweden who were referred for patch testing, 57% (16/28) tested positive for at least 1 acrylate.¹⁷

Modern Sources of Acrylate Exposure

Once thought to be a predominantly occupational exposure, acrylates have rapidly made their way into everyday consumer products. Clinicians should be aware of several sources of clinically relevant acrylate exposure, including nail cosmetics, consumer electronics, and medical/surgical adhesives.

A 2016 study found a shift to nail cosmetics as the most common source of acrylate sensitization.¹⁸ Nail cosmetics that contain acrylates include traditional acrylic, gel (shellac), dipped, and press-on (false) nails.¹⁹ The NACDG found that the most common allergen in patients experiencing ACD associated with nail products (2001-2016) was HEMA (56.6% [273/482]), far ahead of the traditional nail polish allergen tosylamide (36.2% [273/755]). Over the study period, the frequency of positive patch tests statistically increased for HEMA (P=.0069) and decreased for tosylamide (P<.0001).²⁰ There is concern that the use of home gel nail kits, which can be purchased online at the click of a button, may be associated with a risk for acrylate sensitization.^21,22 A recent study surveyed a Facebook support group for individuals with self-reported reactions to nail cosmetics, finding that 78% of the 199 individuals had used at-home gel nail kits, and more than 80% of them first developed skin reactions after starting to use at-home kits.²³ The risks for sensitization are thought to be greater when self-applying nail acrylates compared to having them done professionally because individuals are more likely to spill allergenic monomers onto the skin at home; it also is possible that home techniques could lead to incomplete curing. Table 2 reviews the different types of acrylic nail cosmetics.

Medical adhesives and equipment are other important areas where acrylates can be encountered in abundance. A review by Spencer et al¹⁸ cautioned wound dressings as an up-and-coming source of sensitization, and this has been demonstrated in the literature as coming to fruition.²⁶ Another study identified acrylates in 15 of 16 (94%) tested medical adhesives; among 7 medical adhesives labeled as hypoallergenic, 100% still contained acrylates and/or abietic acid.²⁷ Multiple case reports have described ACD to adhesives of electrocardiogram electrodes containing acrylates.^28-31 Physicians providing care to patients with diabetes mellitus also must be aware of acrylates in glucose monitors and insulin pumps, either found in the adhesives or leaching from the inside of the device to reach the skin.³² Isobornyl acrylate in particular has made quite the name for itself in this sector, being crowned the 2020 Allergen of the Year owing to its key role in cases of ACD to diabetes devices.³

Cyanoacrylate-based tissue adhesives (eg, 2‐octyl cyanoacrylate) are now well documented to cause postoperative ACD.^33,34 Although robust prospective data are limited, studies suggest that 2% to 14% of patients develop postoperative skin reactions following 2-octyl cyanoacrylate application.^35-37 It has been shown that sensitization to tissue adhesives often occurs after the first application, followed by an eruption of ACD as long as a month later, which can create confusion about the nature of the rash for patients and health care providers alike, who may for instance attribute it to infection rather than allergy.³⁸ In the orthopedic literature, a woman with a known history of acrylic nail ACD had knee arthroplasty failure attributed to acrylic bone cement with resolution of the joint symptoms after changing to a cementless device.³⁹

Awareness of the common use of acrylates is important to identify the cause of reactions from products that would otherwise seem nonallergenic. A case of occupational ACD to isobornyl acrylate in UV-cured phone screen protectors has been reported⁴⁰; several cases of ACD to acrylates in headphones^41,42 as well as one related to a wearable fitness device also have been reported.⁴³ Given all these possible sources of exposure, ACD to acrylates should be on your radar.

When to Consider Acrylate ACD

When working up a patient with dermatitis, it is essential to ask about occupational history and hobbies to get a sense of potential contact allergen exposures. The typical presentation of occupational acrylate-associated ACD is hand eczema, specifically involving the fingertips.^5,24,25,44 Acrylate ACD should be considered in patients with nail dystrophy and a history of wearing acrylic nails.⁴⁵ There can even be involvement of the face and eyelids secondary to airborne contact or ectopic spread from the hands.²⁴ Spreading vesicular eruptions associated with adhesives also should raise concern. The Figure depicts several possible presentations of ACD to acrylates. In a time of abundant access to products containing acrylates, dermatologists should consider this allergy in their differential diagnosis and consider patch testing.

Photographs courtesy of Brandon L. Adler, MD.

Patch Testing to Acrylates

The gold standard for ACD diagnosis is patch testing. It should be noted that no acrylates are included in the thin-layer rapid use epicutaneous (T.R.U.E.) test series. Several acrylates are tested in expanded patch test series including the American Contact Dermatitis Society Core Allergen series and North American 80 Comprehensive Series. 2-Hydroxyethyl methacrylate is thought to be the most important screening allergen to test. Ramos et al¹⁶ reported a positive patch test to HEMA in 81% (30/37) of patients who had any type of acrylate allergy.

If initial testing to a limited number of acrylates is negative but clinical suspicion remains high, expanded acrylates/plastics and glue series also are available from commercial patch test suppliers. Testing to an expanded panel of acrylates is especially pertinent to consider in suspected occupational cases given the risk of workplace absenteeism and even disability that come with continued exposure to the allergen. Of note, isobornyl acrylate is not included in the baseline patch test series and must be tested separately, particularly because it usually does not cross-react with other acrylates, and therefore allergy could be missed if not tested on its own.

Acrylates are volatile substances that have been shown to degrade at room temperature and to a lesser degree when refrigerated. Ideally, they should be stored in a freezer and not used beyond their expiration date. Furthermore, it is advised that acrylate patch tests be prepared immediately prior to placement on the patient and to discard the initial extrusion from the syringe, as the concentration at the tip may be decreased.^46,47

With regard to tissue adhesives, the actual product should be tested as-is because these are not commercially available patch test substances.⁴⁸ Occasionally, patients who are sensitized to the tissue adhesive will not react when patch tested on intact skin. If clinical suspicion remains high, scratch patch testing may confirm contact allergy in cases of negative testing on intact skin.⁴⁹

Management and Prevention

Once a diagnosis of ACD secondary to acrylates has been established, counseling patients on allergen avoidance strategies is essential. For (meth)acrylate-allergic patients who want to continue using modern nail products, cyanoacrylate-based options (eg, dipped, press-on nails) can be considered as an alternative, as they do not cross-react, though independent sensitization is still possible. However, traditional nail polish is the safest option to recommend.

The concern with acrylate sensitization extends beyond the immediate issue that brought the patient into your clinic. Dermatologists must counsel patients who are sensitized to acrylates on the possible sequelae of acrylate-containing dental or orthopedic procedures. Oral lichenoid lesions, denture stomatitis, burning mouth syndrome, or even acute facial swelling have been reported following dental work in patients with acrylate allergy.^50-53 Dentists of patients with acrylate ACD should be informed of the diagnosis so acrylates can be avoided during dental work; if unavoidable, all possible steps should be taken to ensure complete curing of the monomers. In the surgical setting, patients sensitized to cyanoacrylate-based tissue adhesives should be offered wound closure alternatives such as sutures or staples.³⁴

In patients with diabetes mellitus who develop ACD to their glucose monitor or insulin pump, ideally they should be switched to a device that does not contain acrylates. Problematically, these devices are constantly being reformulated, and manufacturers do not always divulge their components, which can make it challenging to determine safe alternative options.^32,54 Various barrier products may help on a case-by-case basis.⁵⁵Preventative measures should be implemented in workplaces that utilize acrylates, including dental practices and nail salons. Acrylic monomers have been shown to penetrate most gloves within minutes of exposure.^56,57 Double gloving with nitrile gloves affords some protection for no longer than 60 minutes.⁶ 4H gloves have been shown to provide true protection but result in a loss of dexterity.⁵⁸ The fingerstall technique involves removing the fingers from a 4H glove, inserting them on the fingers, and applying a more flexible glove on top to hold them in place; this offers a hybrid between protection and finger dexterity.⁵⁹

Final Interpretation

In a world characterized by technological advancements and increasing accessibility to acrylate-containing products, we hope this brief review serves as a resource and reminder to dermatologists to consider acrylates as a potential cause of ACD with diverse presentations and important future implications for affected individuals. The rising trend of acrylate allergy necessitates comprehensive assessment and shared decision-making between physicians and patients. As we navigate the ever-changing landscape of materials and technologies, clinicians must remain vigilant to avoid some potentially sticky situations for patients.

Prurigo nodularis (PN), a condition that historically has been a challenge to treat, now has a US Food and Drug Administration (FDA)–approved therapy—dupilumab—with other agents in the pipeline. As clinicians, we recognize PN as typically symmetric, keratotic, papular and nodular lesions presenting in older adults with chronic pruritus; patients with atopic dermatitis make up roughly half of patients with PN, but a workup for pruritus is indicated in other settings.¹ In the United States, Black patients are 3.4-times more likely than White patients to have PN.² The differential diagnosis includes conditions such nodular scabies, pemphigoid nodularis, acquired perforating disorders, and hypertrophic lichen planus, which also should be considered, especially in cases that are refractory to first-line therapies. Recent breakthroughs in therapy have come from substantial progress in our understanding of the pathogenesis of PN as driven by disorders of cytokine expression and/or neurocutaneous aberrations. We review progress in the treatment of PN over the last 3 years.

Treatment Guidelines

In 2020, an expert panel published consensus treatment guidelines for PN.¹ The panel, which proposed a 4-tiered approach targeting both neural and immunologic mechanisms in the pathogenesis of PN, emphasized the importance of tailoring treatment to the individual patient. Topical therapies remained the mainstay of treatment, with agents such as topical capsaicin, ketamine, lidocaine, and amitriptyline targeting the neural component and topical corticosteroids, calcineurin inhibitors, and calcipotriol and intralesional corticosteroids targeting the immunologic component. Phototherapy, methotrexate, cyclosporine, antidepressants, and gabapentinoids used with varying degrees of success were noted to have acceptable tolerability.¹

FDA-Approved Therapy

In September 2022, the FDA approved dupilumab for the treatment of PN. An antagonist of the IL-4 receptor, dupilumab was found to reduce both pruritus and skin lesions over a 24-week period in 2 phase 3 clinical trials.³ Results also demonstrated progressive improvements in measures assessing quality of life and pruritus over the study period, suggesting that continued treatment could lead to even further improvements in these measures. Adverse events were minimal and similar between the dupilumab- and placebo-treated groups.³

The FDA approval of dupilumab is a promising step in decreasing the disease burden of widespread or refractory PN, both for patients and the health care system. The treatment of patients with PN has been more challenging due to comorbidities, including mental health conditions, endocrine disorders, cardiovascular conditions, renal conditions, malignancy, and HIV.^4,5 These comorbidities can complicate the use of traditional systemic and immunosuppressive agents. Dupilumab has virtually no contraindications and has demonstrated safety in almost all patient populations.⁶

Consistent insurance coverage for patients who respond to dupilumab remains to be determined. A review investigating the use of dupilumab in patients with atopic dermatitis at the University of Pittsburgh Medical Center (Pittsburgh, Pennsylvania) found that of 179 patients, 67 (37.4%) did not start dupilumab, mainly due to insurance denial (34/179 [19%]) or copay (20/179 [11%]). Medicare patients were less likely to receive treatment compared to those on private insurance or Medicaid.⁷ In a recent review of 701 patients with PN, the mean age was 64.8 years,⁵ highlighting the concern about obtaining insurance coverage for dupilumab in this population given the higher likelihood that these patients will be on Medicare. Prescribers should be aware that coverage denials are likely and should be prepared to advocate for their patients by citing recent studies to hopefully obtain coverage for dupilumab in the treatment of PN. Resources such as the Dupixent MyWay program (https://www.dupixent.com/support-savings/dupixent-my-way) can provide useful recommendations for pursuing insurance approval for this agent.

Investigation of Janus Kinase Inhibitors

Emerging data suggest that Janus kinase (JAK) inhibitors may be beneficial in the treatment of PN. Patients with refractory PN have been treated off label with the JAK inhibitor tofacitinib at a dosage of 5 mg twice daily with improvement in symptoms and minimal side effects.^8,9 Similarly, a case report showed that off-label use of the JAK inhibitor baricitinib resulted in marked improvement in pruritus and clearance of lesions at a dosage of 4 mg daily, with reduction in pruritus seen as early as 1 week after treatment initiation.¹⁰ Although most patients are able to tolerate JAK inhibitors, known side effects include acne, viral infections, gastrointestinal tract upset, and the potential increased risk for malignancy.¹¹ The use of topical JAK inhibitors such as ruxolitinib has not yet been studied in PN, though cost may limit use to localized disease.

Other New Therapies

Recent case reports and case series have found the vitamin A derivative alitretinoin to be an effective treatment for recalcitrant PN, typically at a dosage of 30 mg daily.^12,13 Sustained remission was noted even after discontinuation of the medication.¹² Alitretinoin, which has been demonstrated to be effective in treating dermatitis,¹⁴ was well tolerated. Similar to JAK inhibitors, there are minimal data investigating the use of topical retinoids in the treatment of localized PN.

Topical cannabinoids have shown benefit in the treatment of pruritus¹⁵ and may be beneficial for the treatment of PN, though there currently are limited data in the literature. With the use of both medical and legal recreational marijuana on the rise, there is an increased interest in cannabinoids, particularly as many patients consider these agents to be more “natural”—and therefore preferable—treatment options. As the use of cannabis derivatives become more commonplace in both traditional and complementary medicine, providers should be prepared to field questions from patients about their potential for PN.

Finally, the IL-31RA inhibitor nemolizumab also has shown promise in the treatment of PN. A recent study suggested that nemolizumab helps modulate inflammatory and neural signaling in PN.¹⁶ Nemolizumab has been granted breakthrough therapy designation for the treatment of pruritus in PN based on a phase 2 study that demonstrated improvement in pruritus and skin lesions in a group of 70 patients with moderate to severe PN.¹⁷ Nemolizumab, which is used to treat pruritus in atopic dermatitis, has minimal side effects including upper respiratory tract infections and peripheral edema.¹⁸

Final Thoughts

Prurigo nodularis historically has been considered difficult to treat, particularly in those with widespread lesions. Dupilumab—the first FDA-approved treatment of PN—is now an exciting option, not just for patients with underlying atopic dermatitis. Not all patients will respond to the medication, and the ease of obtaining insurance approval has yet to be established; therefore, having other treatment options will be imperative. In patients with recalcitrant disease, several other treatment options have shown promise in the treatment of PN; in particular, JAK inhibitors, alitretinoin, and nemolizumab should be considered in patients with widespread refractory PN who are willing to try alternative agents. Ongoing research should be focused on these medications as well as on the development of other novel treatments aimed at relieving affected patients.

Prurigo nodularis (PN), a condition that historically has been a challenge to treat, now has a US Food and Drug Administration (FDA)–approved therapy—dupilumab—with other agents in the pipeline. As clinicians, we recognize PN as typically symmetric, keratotic, papular and nodular lesions presenting in older adults with chronic pruritus; patients with atopic dermatitis make up roughly half of patients with PN, but a workup for pruritus is indicated in other settings.¹ In the United States, Black patients are 3.4-times more likely than White patients to have PN.² The differential diagnosis includes conditions such nodular scabies, pemphigoid nodularis, acquired perforating disorders, and hypertrophic lichen planus, which also should be considered, especially in cases that are refractory to first-line therapies. Recent breakthroughs in therapy have come from substantial progress in our understanding of the pathogenesis of PN as driven by disorders of cytokine expression and/or neurocutaneous aberrations. We review progress in the treatment of PN over the last 3 years.

Treatment Guidelines

In 2020, an expert panel published consensus treatment guidelines for PN.¹ The panel, which proposed a 4-tiered approach targeting both neural and immunologic mechanisms in the pathogenesis of PN, emphasized the importance of tailoring treatment to the individual patient. Topical therapies remained the mainstay of treatment, with agents such as topical capsaicin, ketamine, lidocaine, and amitriptyline targeting the neural component and topical corticosteroids, calcineurin inhibitors, and calcipotriol and intralesional corticosteroids targeting the immunologic component. Phototherapy, methotrexate, cyclosporine, antidepressants, and gabapentinoids used with varying degrees of success were noted to have acceptable tolerability.¹

FDA-Approved Therapy

In September 2022, the FDA approved dupilumab for the treatment of PN. An antagonist of the IL-4 receptor, dupilumab was found to reduce both pruritus and skin lesions over a 24-week period in 2 phase 3 clinical trials.³ Results also demonstrated progressive improvements in measures assessing quality of life and pruritus over the study period, suggesting that continued treatment could lead to even further improvements in these measures. Adverse events were minimal and similar between the dupilumab- and placebo-treated groups.³

The FDA approval of dupilumab is a promising step in decreasing the disease burden of widespread or refractory PN, both for patients and the health care system. The treatment of patients with PN has been more challenging due to comorbidities, including mental health conditions, endocrine disorders, cardiovascular conditions, renal conditions, malignancy, and HIV.^4,5 These comorbidities can complicate the use of traditional systemic and immunosuppressive agents. Dupilumab has virtually no contraindications and has demonstrated safety in almost all patient populations.⁶

Consistent insurance coverage for patients who respond to dupilumab remains to be determined. A review investigating the use of dupilumab in patients with atopic dermatitis at the University of Pittsburgh Medical Center (Pittsburgh, Pennsylvania) found that of 179 patients, 67 (37.4%) did not start dupilumab, mainly due to insurance denial (34/179 [19%]) or copay (20/179 [11%]). Medicare patients were less likely to receive treatment compared to those on private insurance or Medicaid.⁷ In a recent review of 701 patients with PN, the mean age was 64.8 years,⁵ highlighting the concern about obtaining insurance coverage for dupilumab in this population given the higher likelihood that these patients will be on Medicare. Prescribers should be aware that coverage denials are likely and should be prepared to advocate for their patients by citing recent studies to hopefully obtain coverage for dupilumab in the treatment of PN. Resources such as the Dupixent MyWay program (https://www.dupixent.com/support-savings/dupixent-my-way) can provide useful recommendations for pursuing insurance approval for this agent.

Investigation of Janus Kinase Inhibitors

Emerging data suggest that Janus kinase (JAK) inhibitors may be beneficial in the treatment of PN. Patients with refractory PN have been treated off label with the JAK inhibitor tofacitinib at a dosage of 5 mg twice daily with improvement in symptoms and minimal side effects.^8,9 Similarly, a case report showed that off-label use of the JAK inhibitor baricitinib resulted in marked improvement in pruritus and clearance of lesions at a dosage of 4 mg daily, with reduction in pruritus seen as early as 1 week after treatment initiation.¹⁰ Although most patients are able to tolerate JAK inhibitors, known side effects include acne, viral infections, gastrointestinal tract upset, and the potential increased risk for malignancy.¹¹ The use of topical JAK inhibitors such as ruxolitinib has not yet been studied in PN, though cost may limit use to localized disease.

Other New Therapies

Recent case reports and case series have found the vitamin A derivative alitretinoin to be an effective treatment for recalcitrant PN, typically at a dosage of 30 mg daily.^12,13 Sustained remission was noted even after discontinuation of the medication.¹² Alitretinoin, which has been demonstrated to be effective in treating dermatitis,¹⁴ was well tolerated. Similar to JAK inhibitors, there are minimal data investigating the use of topical retinoids in the treatment of localized PN.

Topical cannabinoids have shown benefit in the treatment of pruritus¹⁵ and may be beneficial for the treatment of PN, though there currently are limited data in the literature. With the use of both medical and legal recreational marijuana on the rise, there is an increased interest in cannabinoids, particularly as many patients consider these agents to be more “natural”—and therefore preferable—treatment options. As the use of cannabis derivatives become more commonplace in both traditional and complementary medicine, providers should be prepared to field questions from patients about their potential for PN.

Finally, the IL-31RA inhibitor nemolizumab also has shown promise in the treatment of PN. A recent study suggested that nemolizumab helps modulate inflammatory and neural signaling in PN.¹⁶ Nemolizumab has been granted breakthrough therapy designation for the treatment of pruritus in PN based on a phase 2 study that demonstrated improvement in pruritus and skin lesions in a group of 70 patients with moderate to severe PN.¹⁷ Nemolizumab, which is used to treat pruritus in atopic dermatitis, has minimal side effects including upper respiratory tract infections and peripheral edema.¹⁸

Final Thoughts

Prurigo nodularis historically has been considered difficult to treat, particularly in those with widespread lesions. Dupilumab—the first FDA-approved treatment of PN—is now an exciting option, not just for patients with underlying atopic dermatitis. Not all patients will respond to the medication, and the ease of obtaining insurance approval has yet to be established; therefore, having other treatment options will be imperative. In patients with recalcitrant disease, several other treatment options have shown promise in the treatment of PN; in particular, JAK inhibitors, alitretinoin, and nemolizumab should be considered in patients with widespread refractory PN who are willing to try alternative agents. Ongoing research should be focused on these medications as well as on the development of other novel treatments aimed at relieving affected patients.

Prurigo nodularis (PN), a condition that historically has been a challenge to treat, now has a US Food and Drug Administration (FDA)–approved therapy—dupilumab—with other agents in the pipeline. As clinicians, we recognize PN as typically symmetric, keratotic, papular and nodular lesions presenting in older adults with chronic pruritus; patients with atopic dermatitis make up roughly half of patients with PN, but a workup for pruritus is indicated in other settings.¹ In the United States, Black patients are 3.4-times more likely than White patients to have PN.² The differential diagnosis includes conditions such nodular scabies, pemphigoid nodularis, acquired perforating disorders, and hypertrophic lichen planus, which also should be considered, especially in cases that are refractory to first-line therapies. Recent breakthroughs in therapy have come from substantial progress in our understanding of the pathogenesis of PN as driven by disorders of cytokine expression and/or neurocutaneous aberrations. We review progress in the treatment of PN over the last 3 years.

Treatment Guidelines

In 2020, an expert panel published consensus treatment guidelines for PN.¹ The panel, which proposed a 4-tiered approach targeting both neural and immunologic mechanisms in the pathogenesis of PN, emphasized the importance of tailoring treatment to the individual patient. Topical therapies remained the mainstay of treatment, with agents such as topical capsaicin, ketamine, lidocaine, and amitriptyline targeting the neural component and topical corticosteroids, calcineurin inhibitors, and calcipotriol and intralesional corticosteroids targeting the immunologic component. Phototherapy, methotrexate, cyclosporine, antidepressants, and gabapentinoids used with varying degrees of success were noted to have acceptable tolerability.¹

FDA-Approved Therapy

In September 2022, the FDA approved dupilumab for the treatment of PN. An antagonist of the IL-4 receptor, dupilumab was found to reduce both pruritus and skin lesions over a 24-week period in 2 phase 3 clinical trials.³ Results also demonstrated progressive improvements in measures assessing quality of life and pruritus over the study period, suggesting that continued treatment could lead to even further improvements in these measures. Adverse events were minimal and similar between the dupilumab- and placebo-treated groups.³

The FDA approval of dupilumab is a promising step in decreasing the disease burden of widespread or refractory PN, both for patients and the health care system. The treatment of patients with PN has been more challenging due to comorbidities, including mental health conditions, endocrine disorders, cardiovascular conditions, renal conditions, malignancy, and HIV.^4,5 These comorbidities can complicate the use of traditional systemic and immunosuppressive agents. Dupilumab has virtually no contraindications and has demonstrated safety in almost all patient populations.⁶

Consistent insurance coverage for patients who respond to dupilumab remains to be determined. A review investigating the use of dupilumab in patients with atopic dermatitis at the University of Pittsburgh Medical Center (Pittsburgh, Pennsylvania) found that of 179 patients, 67 (37.4%) did not start dupilumab, mainly due to insurance denial (34/179 [19%]) or copay (20/179 [11%]). Medicare patients were less likely to receive treatment compared to those on private insurance or Medicaid.⁷ In a recent review of 701 patients with PN, the mean age was 64.8 years,⁵ highlighting the concern about obtaining insurance coverage for dupilumab in this population given the higher likelihood that these patients will be on Medicare. Prescribers should be aware that coverage denials are likely and should be prepared to advocate for their patients by citing recent studies to hopefully obtain coverage for dupilumab in the treatment of PN. Resources such as the Dupixent MyWay program (https://www.dupixent.com/support-savings/dupixent-my-way) can provide useful recommendations for pursuing insurance approval for this agent.

Investigation of Janus Kinase Inhibitors

Emerging data suggest that Janus kinase (JAK) inhibitors may be beneficial in the treatment of PN. Patients with refractory PN have been treated off label with the JAK inhibitor tofacitinib at a dosage of 5 mg twice daily with improvement in symptoms and minimal side effects.^8,9 Similarly, a case report showed that off-label use of the JAK inhibitor baricitinib resulted in marked improvement in pruritus and clearance of lesions at a dosage of 4 mg daily, with reduction in pruritus seen as early as 1 week after treatment initiation.¹⁰ Although most patients are able to tolerate JAK inhibitors, known side effects include acne, viral infections, gastrointestinal tract upset, and the potential increased risk for malignancy.¹¹ The use of topical JAK inhibitors such as ruxolitinib has not yet been studied in PN, though cost may limit use to localized disease.

Other New Therapies

Recent case reports and case series have found the vitamin A derivative alitretinoin to be an effective treatment for recalcitrant PN, typically at a dosage of 30 mg daily.^12,13 Sustained remission was noted even after discontinuation of the medication.¹² Alitretinoin, which has been demonstrated to be effective in treating dermatitis,¹⁴ was well tolerated. Similar to JAK inhibitors, there are minimal data investigating the use of topical retinoids in the treatment of localized PN.

Topical cannabinoids have shown benefit in the treatment of pruritus¹⁵ and may be beneficial for the treatment of PN, though there currently are limited data in the literature. With the use of both medical and legal recreational marijuana on the rise, there is an increased interest in cannabinoids, particularly as many patients consider these agents to be more “natural”—and therefore preferable—treatment options. As the use of cannabis derivatives become more commonplace in both traditional and complementary medicine, providers should be prepared to field questions from patients about their potential for PN.

Finally, the IL-31RA inhibitor nemolizumab also has shown promise in the treatment of PN. A recent study suggested that nemolizumab helps modulate inflammatory and neural signaling in PN.¹⁶ Nemolizumab has been granted breakthrough therapy designation for the treatment of pruritus in PN based on a phase 2 study that demonstrated improvement in pruritus and skin lesions in a group of 70 patients with moderate to severe PN.¹⁷ Nemolizumab, which is used to treat pruritus in atopic dermatitis, has minimal side effects including upper respiratory tract infections and peripheral edema.¹⁸

Final Thoughts

Prurigo nodularis historically has been considered difficult to treat, particularly in those with widespread lesions. Dupilumab—the first FDA-approved treatment of PN—is now an exciting option, not just for patients with underlying atopic dermatitis. Not all patients will respond to the medication, and the ease of obtaining insurance approval has yet to be established; therefore, having other treatment options will be imperative. In patients with recalcitrant disease, several other treatment options have shown promise in the treatment of PN; in particular, JAK inhibitors, alitretinoin, and nemolizumab should be considered in patients with widespread refractory PN who are willing to try alternative agents. Ongoing research should be focused on these medications as well as on the development of other novel treatments aimed at relieving affected patients.

Clinical Importance

Dendrocnide moroides is arguably the most brutal of stinging plants, even leading to death in dogs, horses, and humans in rare cases.^1-3 Commonly called gympie-gympie (based on its discovery by gold miners near the town of Gympie in Queensland, Australia), D moroides also has been referred to as the mulberrylike stinging tree or stinger.^2,4-6

Family and Nomenclature

The Australian stinging tree belongs to the family Urticaceae (known as the nettle family) within the order Rosales.^1,2,3,5 Urticaceae is derived from the Latin term urere (to burn)—an apt description of the clinical experience of patients with D moroides–induced urticaria.

Urticaceae includes 54 genera, comprising herbs, shrubs, small trees, and vines found predominantly in tropical regions. Dendrocnide comprises approximately 40 species, all commonly known in Australia as stinging trees.^2,7,8

Distribution

Dendrocnide moroides is found in the rainforests of Australia and Southeast Asia.² Because the plant has a strong need for sunlight and wind protection, it typically is found in light-filled gaps within the rainforest, in moist ravines, along the edges of creeks, and on land bordering the rainforest.^3,6

Appearance

Although D moroides is referred to as a tree, it is an understory shrub that typically grows to 3 m, with heart-shaped, serrated, dark green leaves that are 50-cm wide (Figure 1).⁶ The leaves are produced consistently through the year, with variable growth depending on the season.⁹

Reprinted with permission from Hurley.&lt;sup&gt;6&lt;/sup&gt;

The plant is covered in what appears to be soft downy fur made up of trichomes (or plant hairs).^1,6 The density of the hairs on leaves decreases as they age.^2,9 The fruit, which is actually edible (if one is careful to avoid hairs), appears similar to red to dark purple raspberries growing on long stems.^5,6

Cutaneous Manifestations

Symptoms of contact with the stems and leaves of D moroides range from slight irritation to serious neurologic disorders, including neuropathy. The severity of the reaction depends on the person, how much skin was contacted, and how one came into contact with the plant.^1,5 Upon touch, there is an immediate reaction, with burning, urticaria, and edema. Pain increases, peaking 30 minutes later; then the pain slowly subsides.¹ Tachycardia and throbbing regional lymphadenopathy can occur for 1 to 4 hours.^1,6

Cutaneous Findings—Examination reveals immediate piloerection, erythema due to arteriolar dilation, and local swelling.² These findings may disappear after 1 hour or last as long as 24 hours.¹ Although objective signs may fade, subjective pain, pruritus, and burning can persist for months.³

Dermatitis-Inducing Plant Parts

After contact with the stems or leaves, the sharp trichomes become embedded in the skin, making them difficult to remove.¹ The toxins are contained in siliceous hairs that the human body cannot break down.³ Symptoms can be experienced for as long as 1 year after contact, especially when the skin is pressed firmly or washed with hot or cold water.^3,6 Because the plant’s hairs are shed continuously, being in close proximity to D moroides for longer than 20 minutes can lead to extreme sneezing, nosebleeds, and major respiratory damage from inhaling hairs.^1,6,9

The stinging hairs of D moroides differ from irritant hairs on other plants because they contain physiologically active substances. Stinging hairs are classified as either a hypodermic syringe, which expels liquid only, or as a tragia-type syringe, in which liquid and sharp crystals are injected.

The Australian stinging tree falls into the first of these 2 groups (Figure 2)¹; the sharp tip of the hair breaks on contact, leading to expulsion of the toxin into skin.^1,4 The hairs function as a defense against mammalian herbivores but typically have no impact on pests.¹ Nocturnal beetles and on occasion possums and red-legged pademelons dare to eat D moroides.^3,6

Republished under the Creative Commons Attribution (CC-BY 4.0).&lt;i&gt;1&lt;/i&gt;

The Irritant

Initially, formic acid was proposed as the irritant chemical in D moroides¹; other candidates have included neurotransmitters, such as histamine, acetylcholine, and serotonin, as well as inorganic ions, such as potassium. These compounds may play a role but none explain the persistent sensory effects and years-long stable nature of the toxin.^1,4

The most likely culprit irritant is a member of a newly discovered family of neurotoxins, the gympietides. These knot-shaped chemicals, found in D moroides and some spider venoms, have the ability to activate voltage-gated sodium channels of cutaneous neurons and cause local cutaneous vasodilation by stimulating neurotransmitter release.⁴ These neurotoxins not only generate pain but also suppress the mechanism used to interrupt those pain signals.¹⁰ Synthesized gympietides can replicate the effects of natural contact, indicating that they are the primary active toxins. These toxins are ultrastable, thus producing lasting effects.¹

Although much is understood about the evolution and distribution of D moroides and the ecological role that it plays, there is still more to learn about the plant’s toxicology.

Prevention—Dendrocnide moroides dermatitis is best prevented by avoiding contact with the plant and related species, as well as wearing upper body clothing with long sleeves, pants, and boots, though plant hairs can still penetrate garments and sting.^2,3

Therapy—There is no reversal therapy of D moroides dermatitis but symptoms can be managed.⁴ For pain, analgesics, such as opioids, have been used; on occasion, however, pain is so intense that even morphine does not help.^4,10

Systemic or topical corticosteroids are the main therapy for many forms of plant-induced dermatitis because they are able to decrease cytokine production and stop lymphocyte production. Adding an oral antihistamine can alleviate histamine-mediated pruritus but not pruritus that is mediated by other chemicals.¹¹

Other methods of relieving symptoms of D moroides dermatitis have been proposed or reported anecdotally. Diluted hydrochloric acid can be applied to the skin to denature remaining toxin.⁴ The sap of Alocasia brisbanensis (the cunjevoi plant) can be rubbed on affected areas to provide a cooling effect, but do not allow A brisbanensis sap to enter the mouth, as it contains calcium oxalate, a toxic irritant found in dumb cane (Dieffenbachia species). The roots of the Australian stinging tree also can be ground and made into a paste, which is applied to the skin.³ However, given the stability of the toxin, we do not recommend these remedies.

Instead, heavy-duty masking tape or hot wax can be applied to remove plant hairs from the skin. The most successful method of removing plant hair is hair removal wax strips, which are considered an essential component of a first aid kit where D moroides is found.³

Clinical Importance

Dendrocnide moroides is arguably the most brutal of stinging plants, even leading to death in dogs, horses, and humans in rare cases.^1-3 Commonly called gympie-gympie (based on its discovery by gold miners near the town of Gympie in Queensland, Australia), D moroides also has been referred to as the mulberrylike stinging tree or stinger.^2,4-6

Family and Nomenclature

The Australian stinging tree belongs to the family Urticaceae (known as the nettle family) within the order Rosales.^1,2,3,5 Urticaceae is derived from the Latin term urere (to burn)—an apt description of the clinical experience of patients with D moroides–induced urticaria.

Urticaceae includes 54 genera, comprising herbs, shrubs, small trees, and vines found predominantly in tropical regions. Dendrocnide comprises approximately 40 species, all commonly known in Australia as stinging trees.^2,7,8

Distribution

Dendrocnide moroides is found in the rainforests of Australia and Southeast Asia.² Because the plant has a strong need for sunlight and wind protection, it typically is found in light-filled gaps within the rainforest, in moist ravines, along the edges of creeks, and on land bordering the rainforest.^3,6

Appearance

Although D moroides is referred to as a tree, it is an understory shrub that typically grows to 3 m, with heart-shaped, serrated, dark green leaves that are 50-cm wide (Figure 1).⁶ The leaves are produced consistently through the year, with variable growth depending on the season.⁹

Reprinted with permission from Hurley.&lt;sup&gt;6&lt;/sup&gt;

The plant is covered in what appears to be soft downy fur made up of trichomes (or plant hairs).^1,6 The density of the hairs on leaves decreases as they age.^2,9 The fruit, which is actually edible (if one is careful to avoid hairs), appears similar to red to dark purple raspberries growing on long stems.^5,6

Cutaneous Manifestations

Symptoms of contact with the stems and leaves of D moroides range from slight irritation to serious neurologic disorders, including neuropathy. The severity of the reaction depends on the person, how much skin was contacted, and how one came into contact with the plant.^1,5 Upon touch, there is an immediate reaction, with burning, urticaria, and edema. Pain increases, peaking 30 minutes later; then the pain slowly subsides.¹ Tachycardia and throbbing regional lymphadenopathy can occur for 1 to 4 hours.^1,6

Cutaneous Findings—Examination reveals immediate piloerection, erythema due to arteriolar dilation, and local swelling.² These findings may disappear after 1 hour or last as long as 24 hours.¹ Although objective signs may fade, subjective pain, pruritus, and burning can persist for months.³

Dermatitis-Inducing Plant Parts

After contact with the stems or leaves, the sharp trichomes become embedded in the skin, making them difficult to remove.¹ The toxins are contained in siliceous hairs that the human body cannot break down.³ Symptoms can be experienced for as long as 1 year after contact, especially when the skin is pressed firmly or washed with hot or cold water.^3,6 Because the plant’s hairs are shed continuously, being in close proximity to D moroides for longer than 20 minutes can lead to extreme sneezing, nosebleeds, and major respiratory damage from inhaling hairs.^1,6,9

The stinging hairs of D moroides differ from irritant hairs on other plants because they contain physiologically active substances. Stinging hairs are classified as either a hypodermic syringe, which expels liquid only, or as a tragia-type syringe, in which liquid and sharp crystals are injected.

The Australian stinging tree falls into the first of these 2 groups (Figure 2)¹; the sharp tip of the hair breaks on contact, leading to expulsion of the toxin into skin.^1,4 The hairs function as a defense against mammalian herbivores but typically have no impact on pests.¹ Nocturnal beetles and on occasion possums and red-legged pademelons dare to eat D moroides.^3,6

Republished under the Creative Commons Attribution (CC-BY 4.0).&lt;i&gt;1&lt;/i&gt;

The Irritant

Initially, formic acid was proposed as the irritant chemical in D moroides¹; other candidates have included neurotransmitters, such as histamine, acetylcholine, and serotonin, as well as inorganic ions, such as potassium. These compounds may play a role but none explain the persistent sensory effects and years-long stable nature of the toxin.^1,4

The most likely culprit irritant is a member of a newly discovered family of neurotoxins, the gympietides. These knot-shaped chemicals, found in D moroides and some spider venoms, have the ability to activate voltage-gated sodium channels of cutaneous neurons and cause local cutaneous vasodilation by stimulating neurotransmitter release.⁴ These neurotoxins not only generate pain but also suppress the mechanism used to interrupt those pain signals.¹⁰ Synthesized gympietides can replicate the effects of natural contact, indicating that they are the primary active toxins. These toxins are ultrastable, thus producing lasting effects.¹

Although much is understood about the evolution and distribution of D moroides and the ecological role that it plays, there is still more to learn about the plant’s toxicology.

Prevention—Dendrocnide moroides dermatitis is best prevented by avoiding contact with the plant and related species, as well as wearing upper body clothing with long sleeves, pants, and boots, though plant hairs can still penetrate garments and sting.^2,3

Therapy—There is no reversal therapy of D moroides dermatitis but symptoms can be managed.⁴ For pain, analgesics, such as opioids, have been used; on occasion, however, pain is so intense that even morphine does not help.^4,10

Systemic or topical corticosteroids are the main therapy for many forms of plant-induced dermatitis because they are able to decrease cytokine production and stop lymphocyte production. Adding an oral antihistamine can alleviate histamine-mediated pruritus but not pruritus that is mediated by other chemicals.¹¹

Other methods of relieving symptoms of D moroides dermatitis have been proposed or reported anecdotally. Diluted hydrochloric acid can be applied to the skin to denature remaining toxin.⁴ The sap of Alocasia brisbanensis (the cunjevoi plant) can be rubbed on affected areas to provide a cooling effect, but do not allow A brisbanensis sap to enter the mouth, as it contains calcium oxalate, a toxic irritant found in dumb cane (Dieffenbachia species). The roots of the Australian stinging tree also can be ground and made into a paste, which is applied to the skin.³ However, given the stability of the toxin, we do not recommend these remedies.

Instead, heavy-duty masking tape or hot wax can be applied to remove plant hairs from the skin. The most successful method of removing plant hair is hair removal wax strips, which are considered an essential component of a first aid kit where D moroides is found.³

Clinical Importance

Dendrocnide moroides is arguably the most brutal of stinging plants, even leading to death in dogs, horses, and humans in rare cases.^1-3 Commonly called gympie-gympie (based on its discovery by gold miners near the town of Gympie in Queensland, Australia), D moroides also has been referred to as the mulberrylike stinging tree or stinger.^2,4-6

Family and Nomenclature

The Australian stinging tree belongs to the family Urticaceae (known as the nettle family) within the order Rosales.^1,2,3,5 Urticaceae is derived from the Latin term urere (to burn)—an apt description of the clinical experience of patients with D moroides–induced urticaria.

Urticaceae includes 54 genera, comprising herbs, shrubs, small trees, and vines found predominantly in tropical regions. Dendrocnide comprises approximately 40 species, all commonly known in Australia as stinging trees.^2,7,8

Distribution

Dendrocnide moroides is found in the rainforests of Australia and Southeast Asia.² Because the plant has a strong need for sunlight and wind protection, it typically is found in light-filled gaps within the rainforest, in moist ravines, along the edges of creeks, and on land bordering the rainforest.^3,6

Appearance

Although D moroides is referred to as a tree, it is an understory shrub that typically grows to 3 m, with heart-shaped, serrated, dark green leaves that are 50-cm wide (Figure 1).⁶ The leaves are produced consistently through the year, with variable growth depending on the season.⁹

Reprinted with permission from Hurley.&lt;sup&gt;6&lt;/sup&gt;

The plant is covered in what appears to be soft downy fur made up of trichomes (or plant hairs).^1,6 The density of the hairs on leaves decreases as they age.^2,9 The fruit, which is actually edible (if one is careful to avoid hairs), appears similar to red to dark purple raspberries growing on long stems.^5,6

Cutaneous Manifestations

Symptoms of contact with the stems and leaves of D moroides range from slight irritation to serious neurologic disorders, including neuropathy. The severity of the reaction depends on the person, how much skin was contacted, and how one came into contact with the plant.^1,5 Upon touch, there is an immediate reaction, with burning, urticaria, and edema. Pain increases, peaking 30 minutes later; then the pain slowly subsides.¹ Tachycardia and throbbing regional lymphadenopathy can occur for 1 to 4 hours.^1,6

Cutaneous Findings—Examination reveals immediate piloerection, erythema due to arteriolar dilation, and local swelling.² These findings may disappear after 1 hour or last as long as 24 hours.¹ Although objective signs may fade, subjective pain, pruritus, and burning can persist for months.³

Dermatitis-Inducing Plant Parts

After contact with the stems or leaves, the sharp trichomes become embedded in the skin, making them difficult to remove.¹ The toxins are contained in siliceous hairs that the human body cannot break down.³ Symptoms can be experienced for as long as 1 year after contact, especially when the skin is pressed firmly or washed with hot or cold water.^3,6 Because the plant’s hairs are shed continuously, being in close proximity to D moroides for longer than 20 minutes can lead to extreme sneezing, nosebleeds, and major respiratory damage from inhaling hairs.^1,6,9

The stinging hairs of D moroides differ from irritant hairs on other plants because they contain physiologically active substances. Stinging hairs are classified as either a hypodermic syringe, which expels liquid only, or as a tragia-type syringe, in which liquid and sharp crystals are injected.

The Australian stinging tree falls into the first of these 2 groups (Figure 2)¹; the sharp tip of the hair breaks on contact, leading to expulsion of the toxin into skin.^1,4 The hairs function as a defense against mammalian herbivores but typically have no impact on pests.¹ Nocturnal beetles and on occasion possums and red-legged pademelons dare to eat D moroides.^3,6

Republished under the Creative Commons Attribution (CC-BY 4.0).&lt;i&gt;1&lt;/i&gt;

The Irritant

Initially, formic acid was proposed as the irritant chemical in D moroides¹; other candidates have included neurotransmitters, such as histamine, acetylcholine, and serotonin, as well as inorganic ions, such as potassium. These compounds may play a role but none explain the persistent sensory effects and years-long stable nature of the toxin.^1,4

The most likely culprit irritant is a member of a newly discovered family of neurotoxins, the gympietides. These knot-shaped chemicals, found in D moroides and some spider venoms, have the ability to activate voltage-gated sodium channels of cutaneous neurons and cause local cutaneous vasodilation by stimulating neurotransmitter release.⁴ These neurotoxins not only generate pain but also suppress the mechanism used to interrupt those pain signals.¹⁰ Synthesized gympietides can replicate the effects of natural contact, indicating that they are the primary active toxins. These toxins are ultrastable, thus producing lasting effects.¹

Although much is understood about the evolution and distribution of D moroides and the ecological role that it plays, there is still more to learn about the plant’s toxicology.

Prevention—Dendrocnide moroides dermatitis is best prevented by avoiding contact with the plant and related species, as well as wearing upper body clothing with long sleeves, pants, and boots, though plant hairs can still penetrate garments and sting.^2,3

Therapy—There is no reversal therapy of D moroides dermatitis but symptoms can be managed.⁴ For pain, analgesics, such as opioids, have been used; on occasion, however, pain is so intense that even morphine does not help.^4,10

Systemic or topical corticosteroids are the main therapy for many forms of plant-induced dermatitis because they are able to decrease cytokine production and stop lymphocyte production. Adding an oral antihistamine can alleviate histamine-mediated pruritus but not pruritus that is mediated by other chemicals.¹¹

Other methods of relieving symptoms of D moroides dermatitis have been proposed or reported anecdotally. Diluted hydrochloric acid can be applied to the skin to denature remaining toxin.⁴ The sap of Alocasia brisbanensis (the cunjevoi plant) can be rubbed on affected areas to provide a cooling effect, but do not allow A brisbanensis sap to enter the mouth, as it contains calcium oxalate, a toxic irritant found in dumb cane (Dieffenbachia species). The roots of the Australian stinging tree also can be ground and made into a paste, which is applied to the skin.³ However, given the stability of the toxin, we do not recommend these remedies.

Instead, heavy-duty masking tape or hot wax can be applied to remove plant hairs from the skin. The most successful method of removing plant hair is hair removal wax strips, which are considered an essential component of a first aid kit where D moroides is found.³

Children with atopic dermatitis (AD) were significantly more likely to have positive patch test results than were children without AD, according to a study of over 900 children evaluated for allergic contact dermatitis (ACD) with patch testing, a finding that investigators say underscores the value of considering ACD in patients with AD and referring more children for testing.

ACD is underdetected in children with AD. In some cases, it may be misconstrued to be AD, and patch testing, the gold standard for diagnosing ACD, is often not performed, said senior author JiaDe Yu, MD, MS, a pediatric dermatologist and director of contact and occupational dermatology at Massachusetts General Hospital, Boston, and his co-authors, in the study published in the Journal of the American Academy of Dermatology.

Dr. JiaDe Yu

UCHealth

Top allergens

The top 10 allergens between children with and without AD were largely similar, the authors of the study report. Nickel was the most common allergen identified in both groups, and cobalt was in the top five for both groups. Fragrances (including hydroperoxides of linalool), preservatives (including methylisothiazolinone [MI]), and neomycin ranked in the top 10 in both groups, though prevalence differed.

MI, a preservative frequently used in personal care products and in other products like school glue and paint, was the second most common allergen identified in children with AD. Allergy to MI has “recently become an epidemic in the United States, with rapidly increasing prevalence and importance as a source of ACD among both children and adults,” the authors note.

Children with AD were significantly more likely, however, to have ACD to bacitracin (OR, 3.23; P = .030) and to cocamidopropyl betaine (OR, 3.69; P = .0007), the latter of which is a popular surfactant used in “baby” and “gentle” skincare products. This is unsurprising, given that children with AD are “more often exposed to a myriad of topical treatments,” Dr. Yu and his colleagues write.

Although not a top 10 allergen for either group, ACD to “carba mix,” a combination of three chemicals used to make medical adhesives and other rubber products (such as pacifiers, toys, school supplies, and rubber gloves) was significantly more common in children with AD than in those without (OR, 3.36; P = .025).

Among other findings from the study: Children with AD were more likely to have a longer history of dermatitis (4.1 vs. 1.6 years, P < .0001) prior to patch testing. Testing occurred at a mean age of 11 and 12.3 years for children with and without AD, respectively.

The number of allergens tested and the patch testing series chosen per patient were “not statistically different” between the children with and without AD, the researchers report.

Patch testing availability

Clinicians may be hesitant to subject a child to patch testing, but the process is well tolerated in most children, Dr. Perryman said. She uses a modified panel for children that omits less relevant allergens and usually limits patch testing to age 2 years or older due to a young child’s smaller surface area.

Dr. Yu, who developed an interest in patch testing during his residency at the Medical College of Wisconsin, Milwaukee, where he worked with a patch-testing expert, will test children as young as 3-4 months with a “small selection of patches.”

The challenge with a call for more patch testing is a shortage of trained physicians. “In all of Boston, where we have hundreds of dermatologists, there are only about four of us who really do patch testing. My wait time is about 6 months,” said Dr. Yu, who is also an assistant professor at Harvard Medical School, Boston.

Allergists at Massachusetts General Hospital do “some patch testing ... but they refer a lot of the most complicated cases to me,” he said, noting that patch testing and management of ACD involves detailed counseling for patients about avoidance of allergens. “Overall dermatologists represent the largest group of doctors who have proficiency in patch testing, and there just aren’t many of us.”

Dr. Perryman also said that patch testing is often performed by dermatologists who specialize in treating ACD and AD, though there seems to be “regional variance” in the level of involvement of dermatologists and allergists in patch testing.

Not all residency programs have hands-on patch testing opportunities, Dr. Yu said. A study published in Dermatitis, which he co-authored, showed that in 2020, 47.5% of dermatology residency programs had formal patch testing rotations. This represented improvement but is still not enough, he said.

The American Contact Dermatitis Society offers patch-testing mentorship programs, and the American Academy of Dermatology has recently begun offered a patch testing workshop at its annual meetings, said Dr. Yu, who received 4 weeks of training in the Society’s mentorship program and is now involved in the American Academy of Dermatology’s workshops and as a trainer/lecturer at the Contact Dermatitis Institute.

The study was supported by the Dermatology Foundation. Dr. Yu and his co-investigators reported no conflicts of interest. Dr. Perryman had no disclosures.

A version of this article first appeared on Medscape.com.

Children with atopic dermatitis (AD) were significantly more likely to have positive patch test results than were children without AD, according to a study of over 900 children evaluated for allergic contact dermatitis (ACD) with patch testing, a finding that investigators say underscores the value of considering ACD in patients with AD and referring more children for testing.

ACD is underdetected in children with AD. In some cases, it may be misconstrued to be AD, and patch testing, the gold standard for diagnosing ACD, is often not performed, said senior author JiaDe Yu, MD, MS, a pediatric dermatologist and director of contact and occupational dermatology at Massachusetts General Hospital, Boston, and his co-authors, in the study published in the Journal of the American Academy of Dermatology.

Dr. JiaDe Yu

UCHealth

Top allergens

The top 10 allergens between children with and without AD were largely similar, the authors of the study report. Nickel was the most common allergen identified in both groups, and cobalt was in the top five for both groups. Fragrances (including hydroperoxides of linalool), preservatives (including methylisothiazolinone [MI]), and neomycin ranked in the top 10 in both groups, though prevalence differed.

MI, a preservative frequently used in personal care products and in other products like school glue and paint, was the second most common allergen identified in children with AD. Allergy to MI has “recently become an epidemic in the United States, with rapidly increasing prevalence and importance as a source of ACD among both children and adults,” the authors note.

Children with AD were significantly more likely, however, to have ACD to bacitracin (OR, 3.23; P = .030) and to cocamidopropyl betaine (OR, 3.69; P = .0007), the latter of which is a popular surfactant used in “baby” and “gentle” skincare products. This is unsurprising, given that children with AD are “more often exposed to a myriad of topical treatments,” Dr. Yu and his colleagues write.

Although not a top 10 allergen for either group, ACD to “carba mix,” a combination of three chemicals used to make medical adhesives and other rubber products (such as pacifiers, toys, school supplies, and rubber gloves) was significantly more common in children with AD than in those without (OR, 3.36; P = .025).

Among other findings from the study: Children with AD were more likely to have a longer history of dermatitis (4.1 vs. 1.6 years, P < .0001) prior to patch testing. Testing occurred at a mean age of 11 and 12.3 years for children with and without AD, respectively.

The number of allergens tested and the patch testing series chosen per patient were “not statistically different” between the children with and without AD, the researchers report.

Patch testing availability

Clinicians may be hesitant to subject a child to patch testing, but the process is well tolerated in most children, Dr. Perryman said. She uses a modified panel for children that omits less relevant allergens and usually limits patch testing to age 2 years or older due to a young child’s smaller surface area.

Dr. Yu, who developed an interest in patch testing during his residency at the Medical College of Wisconsin, Milwaukee, where he worked with a patch-testing expert, will test children as young as 3-4 months with a “small selection of patches.”

The challenge with a call for more patch testing is a shortage of trained physicians. “In all of Boston, where we have hundreds of dermatologists, there are only about four of us who really do patch testing. My wait time is about 6 months,” said Dr. Yu, who is also an assistant professor at Harvard Medical School, Boston.

Allergists at Massachusetts General Hospital do “some patch testing ... but they refer a lot of the most complicated cases to me,” he said, noting that patch testing and management of ACD involves detailed counseling for patients about avoidance of allergens. “Overall dermatologists represent the largest group of doctors who have proficiency in patch testing, and there just aren’t many of us.”

Dr. Perryman also said that patch testing is often performed by dermatologists who specialize in treating ACD and AD, though there seems to be “regional variance” in the level of involvement of dermatologists and allergists in patch testing.

Not all residency programs have hands-on patch testing opportunities, Dr. Yu said. A study published in Dermatitis, which he co-authored, showed that in 2020, 47.5% of dermatology residency programs had formal patch testing rotations. This represented improvement but is still not enough, he said.

The American Contact Dermatitis Society offers patch-testing mentorship programs, and the American Academy of Dermatology has recently begun offered a patch testing workshop at its annual meetings, said Dr. Yu, who received 4 weeks of training in the Society’s mentorship program and is now involved in the American Academy of Dermatology’s workshops and as a trainer/lecturer at the Contact Dermatitis Institute.

The study was supported by the Dermatology Foundation. Dr. Yu and his co-investigators reported no conflicts of interest. Dr. Perryman had no disclosures.

A version of this article first appeared on Medscape.com.

Children with atopic dermatitis (AD) were significantly more likely to have positive patch test results than were children without AD, according to a study of over 900 children evaluated for allergic contact dermatitis (ACD) with patch testing, a finding that investigators say underscores the value of considering ACD in patients with AD and referring more children for testing.

ACD is underdetected in children with AD. In some cases, it may be misconstrued to be AD, and patch testing, the gold standard for diagnosing ACD, is often not performed, said senior author JiaDe Yu, MD, MS, a pediatric dermatologist and director of contact and occupational dermatology at Massachusetts General Hospital, Boston, and his co-authors, in the study published in the Journal of the American Academy of Dermatology.

Dr. JiaDe Yu

UCHealth

Top allergens

The top 10 allergens between children with and without AD were largely similar, the authors of the study report. Nickel was the most common allergen identified in both groups, and cobalt was in the top five for both groups. Fragrances (including hydroperoxides of linalool), preservatives (including methylisothiazolinone [MI]), and neomycin ranked in the top 10 in both groups, though prevalence differed.

MI, a preservative frequently used in personal care products and in other products like school glue and paint, was the second most common allergen identified in children with AD. Allergy to MI has “recently become an epidemic in the United States, with rapidly increasing prevalence and importance as a source of ACD among both children and adults,” the authors note.

Children with AD were significantly more likely, however, to have ACD to bacitracin (OR, 3.23; P = .030) and to cocamidopropyl betaine (OR, 3.69; P = .0007), the latter of which is a popular surfactant used in “baby” and “gentle” skincare products. This is unsurprising, given that children with AD are “more often exposed to a myriad of topical treatments,” Dr. Yu and his colleagues write.

Although not a top 10 allergen for either group, ACD to “carba mix,” a combination of three chemicals used to make medical adhesives and other rubber products (such as pacifiers, toys, school supplies, and rubber gloves) was significantly more common in children with AD than in those without (OR, 3.36; P = .025).

Among other findings from the study: Children with AD were more likely to have a longer history of dermatitis (4.1 vs. 1.6 years, P < .0001) prior to patch testing. Testing occurred at a mean age of 11 and 12.3 years for children with and without AD, respectively.

The number of allergens tested and the patch testing series chosen per patient were “not statistically different” between the children with and without AD, the researchers report.

Patch testing availability

Clinicians may be hesitant to subject a child to patch testing, but the process is well tolerated in most children, Dr. Perryman said. She uses a modified panel for children that omits less relevant allergens and usually limits patch testing to age 2 years or older due to a young child’s smaller surface area.

Dr. Yu, who developed an interest in patch testing during his residency at the Medical College of Wisconsin, Milwaukee, where he worked with a patch-testing expert, will test children as young as 3-4 months with a “small selection of patches.”

The challenge with a call for more patch testing is a shortage of trained physicians. “In all of Boston, where we have hundreds of dermatologists, there are only about four of us who really do patch testing. My wait time is about 6 months,” said Dr. Yu, who is also an assistant professor at Harvard Medical School, Boston.

Allergists at Massachusetts General Hospital do “some patch testing ... but they refer a lot of the most complicated cases to me,” he said, noting that patch testing and management of ACD involves detailed counseling for patients about avoidance of allergens. “Overall dermatologists represent the largest group of doctors who have proficiency in patch testing, and there just aren’t many of us.”

Dr. Perryman also said that patch testing is often performed by dermatologists who specialize in treating ACD and AD, though there seems to be “regional variance” in the level of involvement of dermatologists and allergists in patch testing.

Not all residency programs have hands-on patch testing opportunities, Dr. Yu said. A study published in Dermatitis, which he co-authored, showed that in 2020, 47.5% of dermatology residency programs had formal patch testing rotations. This represented improvement but is still not enough, he said.

The American Contact Dermatitis Society offers patch-testing mentorship programs, and the American Academy of Dermatology has recently begun offered a patch testing workshop at its annual meetings, said Dr. Yu, who received 4 weeks of training in the Society’s mentorship program and is now involved in the American Academy of Dermatology’s workshops and as a trainer/lecturer at the Contact Dermatitis Institute.

The study was supported by the Dermatology Foundation. Dr. Yu and his co-investigators reported no conflicts of interest. Dr. Perryman had no disclosures.

A version of this article first appeared on Medscape.com.

The tropical rat mite (Ornithonyssus bacoti) belongs to the family Macronyssidae. Theses mites are commonly mistaken for red bird mites or Nordic bird mites because they belong to the same family and have similar characteristics.¹ Although O bacoti is called the tropical rat mite, it also can be found in moderate climates.^2,3

Characteristics

The life cycle of a tropical rat mite lasts 11 to 13 days and includes 5 stages: egg, larva, protonymph, deutonymph, and adult.^1,2 The length of the mite (0.3–0.7 mm) varies with the stage of development.¹ Adults can reach 0.75 to 1.40 mm, with females larger than males and possibly visible with the naked eye.^1,2

Two or 3 days after a blood meal, the female mite lays approximately 100 eggs in its nest but not on the surface of a host. The eggs hatch into larvae after 1 to 4 days and go on to complete their life cyle.¹ During developmental stages, mites occupy their hosts for blood meals. Mites search for their hosts at night and prefer wild or pet rodents for blood meals but are not host specific and can be found on many mammals including birds, cats, racoons, and squirrels.⁴

Although tropical rat mites prefer rodent hosts, they can infest humans when their preferred host is unavailable. In the United States, the first case of human dermatitis due to a tropical rate mite occurred in 1923. In Europe, rat mite dermatitis was first reported in a human in 1931, possibly due to contamination of sailing vessels.⁴

Infestation and Transmission

Tropical rat mites prefer wild and pet rodents as hosts because the mites are able to feed on their blood over long periods.⁴ During the day, the mite spends most of its time hiding in dark dry spaces; it is most active during the night, traveling to find a host for meals.^3-5 If a preferred host is not present, the mite may choose to infest a human.⁵

Human infestation occurs most often upon close bodily contact with an infected animal or pet rodent that was sold without parasites having been eliminated.^3-5 Mites are able to survive without a host for as long as 6 months; they may travel after a meal.^1,2 Therefore, individuals who do not have a pet rodent can be infested if an infected wild rodent has infested their living space.^1,3-5

Clinical Presentation of Infestation

Patients infested with tropical rat mites present with pruritic cutaneous lesions, most often on unclothed parts of the body that are easily exposed to mites; lesions rarely occur on the scalp.⁵ People of any age or gender can be infested. Rat mite bites can present as single or grouped, pruritic, erythematous papules ranging in size from 4 to 10 mm in diameter.^5-7 Excoriations may be present due to excessive scratching. Although rare, vesicles or nodules have been reported.^5,7

Diagnosis of the underlying cause of the cutaneous manifestations often is difficult because mites are not visible during the day, as they are less active then.² Lesions often are misdiagnosed as an allergic response, a bacterial infection, or various forms of dermatitis.¹ A parasitic cause often is not considered unless the physician or patient detects a mite or many trials of therapies fail to provide relief.^1,3-5 Eliciting a thorough history may disclose that the patient has had close contact with rodents or lives in a community center, shelter, or shared space. If any of the patient’s close contacts have a similar presentation, infestation with mites should be considered.

Patients should be educated about treatment options and measures that need to be taken to prevent reinfection. It has been reported that tropical rat mites can survive without a blood meal for as long as 6 months; therefore, meticulous inspection and decontamination of all living spaces is required.^1,4 Once identified, physicians may prescribe an antiparasitic such as permethrin or pyriproxyfen to prevent further infestation and eliminate mites on the host.⁵ Lindane and benzyl benzoate previously were reported to be effective but should be prescribed only in correctly diagnosed cases due to the potential adverse effects of both therapies.^4,7-10 For effective treatment, physicians should thoroughly review the proper application of topical treatments with patients. Topical creams should be massaged into the skin from the head to the soles of the feet, covering all creases of the skin and between the fingers and toes. Antiparasitic creams should be left on the skin for 8 to 14 hours, and all members of the household should be examined and treated, if necessary, by a physician. A thorough bath removes tropical rat mites, but preventive measures should be taken to prevent reinfestation.⁴ Antihistamines or glucocorticoids also can be used as symptomatic treatment.^6,8

Avoiding Reinfestation—Preventive measures should be taken to prevent reinfestation, including evaluation by an exterminator for any wild rodents to remove nests and treat the living space with an acaricide.⁵ Insecticides administered by exterminators, including malathion, methyl carbamate, and lindane, also have been reported to be effective for preventing reinfestation.^5,7-9 A veterinarian should be consulted if the patient owns any pets to ensure proper identification of any potential tropical rat mites and treatments that may be necessary for any household pets.¹

Case Report

A 68-year-old man presented to the dermatology outpatient clinic with diffuse pruritus of the skin and scalp. He reported no other symptoms and had never had a total-body skin examination. His primary care physician recently prescribed a dose pack of methylprednisolone 4-mg tablets, which relieved the symptoms except for a mild scalp itch. His wife did not experience itching, and he denied noticing mites or fleas on his pet dog. Physical examination did not reveal any contributory findings, such as erythema or rash. Ketoconazole shampoo 2% and fluocinolone solution 0.01% were prescribed for scalp pruritus; however, he could not afford those medications and therefore did not take them.

Two weeks later, the patient presented with diffuse itching that involved the scalp, trunk, and extremities. He denied groin pruritus. He reported that the itching was worse at night. His wife continued to be asymptomatic. The patient reported that his health screening was up-to-date, and he had no interval health changes. A complete blood cell count, thyroid studies, and a comprehensive metabolic panel performed recently were within reference range. He denied recent travel or taking new medications. Physical examination revealed a somewhat linear distribution of erythematous urticarial papules on the right side of the abdomen. Red dermatographic excoriations were noted on the back. No burrows were visualized. He was given intramuscular triamcinolone 60 mg and was advised to have his house evaluated for bed bugs and his pet dog evaluated by a veterinarian for mites. During the triamcinolone injection, the medical assistant observed a 1- to 2-mm red insect, which fell into his clothing and could not be further evaluated.

After 1 month, the patient had no improvement of the pruritus; instead, it became worse. During this time, his wife developed intermittent urticarial-like eruptions. He was taking oral diphenhydramine nightly and applying triamcinolone cream 0.5% that he had at home from an earlier skin problem as needed. Physical examination findings correlated with worsening symptoms. He had multiple erythematous urticarial papules—many of which were excoriated—across the chest, abdomen, buttocks, and back. The arms had multiple excoriations. The urticarial papules coalesced in the anterior axillary folds, yet no burrows were visualized. In the left anterior axillary fold adjacent to one of the urticarial papules, a 1-mm mobile mite was identified on dermoscopy. Further evaluation by microscopy showed morphologic characteristics of a tropical rat mite (Figure). The patient admitted that his house had a mouse infestation that he was struggling to eliminate. Permethrin cream 5% was prescribed. Because the patient could not afford the prescription, he was advised to use the triamcinolone cream 0.5%and oral diphenhydramine that he had at home nightly for symptomatic relief. He was advised to hire an exterminator to eradicate the mouse and mite infestation to prevent reinfestation.

Identification of Rate Mite Dermatitis

The characteristics of tropical rat mite dermatitis can be confused with many other conditions, such as infection. Even when a mite is identified, it can be difficult to classify it as a tropical rat mite. To confirm the diagnosis of tropical rat mite dermatitis, the parasite needs to be identified. Skin scrapings can be collected from pruritic lesions and examined microscopically in the hope of revealing the rat mites. The recommendation is to collect skin scrapings from the dorsal aspect of the hands or from the neck.⁵ Patients may report finding mites in their living space or on their bedding or clothing.

Although the tropical rat mite was reported as a vector for endemic typhus between humans, no other cases of transmission between humans have been reported since.^11,12 Studies reporting non–human subject research and case reports have shown that O bacoti is a vector for Rickettsia akari, Coxiella burnetii, Francisella tularensis, Yersinia pestis, Eastern equine encephalitis virus (Alphavirus), Enterovirus (Picornaviridae), Langat virus (Flavivirus), and Hantaan orthohantavirus.^5,11-17 However, no cases of these infectious diseases being transmitted naturally have been reported.⁵

Confirmation of O bacoti as a vector for human pathogens is difficult because it relies on identification of the mite in the clinic.⁵ The epidemiologic importance of the mite in transmitting infectious disease is unknown; reports of human cases of mite infestation are rare. We present this information to increase awareness and help dermatologists and other health care providers identify O bacoti.

The tropical rat mite (Ornithonyssus bacoti) belongs to the family Macronyssidae. Theses mites are commonly mistaken for red bird mites or Nordic bird mites because they belong to the same family and have similar characteristics.¹ Although O bacoti is called the tropical rat mite, it also can be found in moderate climates.^2,3

Characteristics

The life cycle of a tropical rat mite lasts 11 to 13 days and includes 5 stages: egg, larva, protonymph, deutonymph, and adult.^1,2 The length of the mite (0.3–0.7 mm) varies with the stage of development.¹ Adults can reach 0.75 to 1.40 mm, with females larger than males and possibly visible with the naked eye.^1,2

Two or 3 days after a blood meal, the female mite lays approximately 100 eggs in its nest but not on the surface of a host. The eggs hatch into larvae after 1 to 4 days and go on to complete their life cyle.¹ During developmental stages, mites occupy their hosts for blood meals. Mites search for their hosts at night and prefer wild or pet rodents for blood meals but are not host specific and can be found on many mammals including birds, cats, racoons, and squirrels.⁴

Although tropical rat mites prefer rodent hosts, they can infest humans when their preferred host is unavailable. In the United States, the first case of human dermatitis due to a tropical rate mite occurred in 1923. In Europe, rat mite dermatitis was first reported in a human in 1931, possibly due to contamination of sailing vessels.⁴

Infestation and Transmission

Tropical rat mites prefer wild and pet rodents as hosts because the mites are able to feed on their blood over long periods.⁴ During the day, the mite spends most of its time hiding in dark dry spaces; it is most active during the night, traveling to find a host for meals.^3-5 If a preferred host is not present, the mite may choose to infest a human.⁵

Human infestation occurs most often upon close bodily contact with an infected animal or pet rodent that was sold without parasites having been eliminated.^3-5 Mites are able to survive without a host for as long as 6 months; they may travel after a meal.^1,2 Therefore, individuals who do not have a pet rodent can be infested if an infected wild rodent has infested their living space.^1,3-5

Clinical Presentation of Infestation

Patients infested with tropical rat mites present with pruritic cutaneous lesions, most often on unclothed parts of the body that are easily exposed to mites; lesions rarely occur on the scalp.⁵ People of any age or gender can be infested. Rat mite bites can present as single or grouped, pruritic, erythematous papules ranging in size from 4 to 10 mm in diameter.^5-7 Excoriations may be present due to excessive scratching. Although rare, vesicles or nodules have been reported.^5,7

Diagnosis of the underlying cause of the cutaneous manifestations often is difficult because mites are not visible during the day, as they are less active then.² Lesions often are misdiagnosed as an allergic response, a bacterial infection, or various forms of dermatitis.¹ A parasitic cause often is not considered unless the physician or patient detects a mite or many trials of therapies fail to provide relief.^1,3-5 Eliciting a thorough history may disclose that the patient has had close contact with rodents or lives in a community center, shelter, or shared space. If any of the patient’s close contacts have a similar presentation, infestation with mites should be considered.

Patients should be educated about treatment options and measures that need to be taken to prevent reinfection. It has been reported that tropical rat mites can survive without a blood meal for as long as 6 months; therefore, meticulous inspection and decontamination of all living spaces is required.^1,4 Once identified, physicians may prescribe an antiparasitic such as permethrin or pyriproxyfen to prevent further infestation and eliminate mites on the host.⁵ Lindane and benzyl benzoate previously were reported to be effective but should be prescribed only in correctly diagnosed cases due to the potential adverse effects of both therapies.^4,7-10 For effective treatment, physicians should thoroughly review the proper application of topical treatments with patients. Topical creams should be massaged into the skin from the head to the soles of the feet, covering all creases of the skin and between the fingers and toes. Antiparasitic creams should be left on the skin for 8 to 14 hours, and all members of the household should be examined and treated, if necessary, by a physician. A thorough bath removes tropical rat mites, but preventive measures should be taken to prevent reinfestation.⁴ Antihistamines or glucocorticoids also can be used as symptomatic treatment.^6,8

Avoiding Reinfestation—Preventive measures should be taken to prevent reinfestation, including evaluation by an exterminator for any wild rodents to remove nests and treat the living space with an acaricide.⁵ Insecticides administered by exterminators, including malathion, methyl carbamate, and lindane, also have been reported to be effective for preventing reinfestation.^5,7-9 A veterinarian should be consulted if the patient owns any pets to ensure proper identification of any potential tropical rat mites and treatments that may be necessary for any household pets.¹

Case Report

A 68-year-old man presented to the dermatology outpatient clinic with diffuse pruritus of the skin and scalp. He reported no other symptoms and had never had a total-body skin examination. His primary care physician recently prescribed a dose pack of methylprednisolone 4-mg tablets, which relieved the symptoms except for a mild scalp itch. His wife did not experience itching, and he denied noticing mites or fleas on his pet dog. Physical examination did not reveal any contributory findings, such as erythema or rash. Ketoconazole shampoo 2% and fluocinolone solution 0.01% were prescribed for scalp pruritus; however, he could not afford those medications and therefore did not take them.

Two weeks later, the patient presented with diffuse itching that involved the scalp, trunk, and extremities. He denied groin pruritus. He reported that the itching was worse at night. His wife continued to be asymptomatic. The patient reported that his health screening was up-to-date, and he had no interval health changes. A complete blood cell count, thyroid studies, and a comprehensive metabolic panel performed recently were within reference range. He denied recent travel or taking new medications. Physical examination revealed a somewhat linear distribution of erythematous urticarial papules on the right side of the abdomen. Red dermatographic excoriations were noted on the back. No burrows were visualized. He was given intramuscular triamcinolone 60 mg and was advised to have his house evaluated for bed bugs and his pet dog evaluated by a veterinarian for mites. During the triamcinolone injection, the medical assistant observed a 1- to 2-mm red insect, which fell into his clothing and could not be further evaluated.

After 1 month, the patient had no improvement of the pruritus; instead, it became worse. During this time, his wife developed intermittent urticarial-like eruptions. He was taking oral diphenhydramine nightly and applying triamcinolone cream 0.5% that he had at home from an earlier skin problem as needed. Physical examination findings correlated with worsening symptoms. He had multiple erythematous urticarial papules—many of which were excoriated—across the chest, abdomen, buttocks, and back. The arms had multiple excoriations. The urticarial papules coalesced in the anterior axillary folds, yet no burrows were visualized. In the left anterior axillary fold adjacent to one of the urticarial papules, a 1-mm mobile mite was identified on dermoscopy. Further evaluation by microscopy showed morphologic characteristics of a tropical rat mite (Figure). The patient admitted that his house had a mouse infestation that he was struggling to eliminate. Permethrin cream 5% was prescribed. Because the patient could not afford the prescription, he was advised to use the triamcinolone cream 0.5%and oral diphenhydramine that he had at home nightly for symptomatic relief. He was advised to hire an exterminator to eradicate the mouse and mite infestation to prevent reinfestation.

Identification of Rate Mite Dermatitis

The characteristics of tropical rat mite dermatitis can be confused with many other conditions, such as infection. Even when a mite is identified, it can be difficult to classify it as a tropical rat mite. To confirm the diagnosis of tropical rat mite dermatitis, the parasite needs to be identified. Skin scrapings can be collected from pruritic lesions and examined microscopically in the hope of revealing the rat mites. The recommendation is to collect skin scrapings from the dorsal aspect of the hands or from the neck.⁵ Patients may report finding mites in their living space or on their bedding or clothing.

Although the tropical rat mite was reported as a vector for endemic typhus between humans, no other cases of transmission between humans have been reported since.^11,12 Studies reporting non–human subject research and case reports have shown that O bacoti is a vector for Rickettsia akari, Coxiella burnetii, Francisella tularensis, Yersinia pestis, Eastern equine encephalitis virus (Alphavirus), Enterovirus (Picornaviridae), Langat virus (Flavivirus), and Hantaan orthohantavirus.^5,11-17 However, no cases of these infectious diseases being transmitted naturally have been reported.⁵

Confirmation of O bacoti as a vector for human pathogens is difficult because it relies on identification of the mite in the clinic.⁵ The epidemiologic importance of the mite in transmitting infectious disease is unknown; reports of human cases of mite infestation are rare. We present this information to increase awareness and help dermatologists and other health care providers identify O bacoti.

The tropical rat mite (Ornithonyssus bacoti) belongs to the family Macronyssidae. Theses mites are commonly mistaken for red bird mites or Nordic bird mites because they belong to the same family and have similar characteristics.¹ Although O bacoti is called the tropical rat mite, it also can be found in moderate climates.^2,3

Characteristics

The life cycle of a tropical rat mite lasts 11 to 13 days and includes 5 stages: egg, larva, protonymph, deutonymph, and adult.^1,2 The length of the mite (0.3–0.7 mm) varies with the stage of development.¹ Adults can reach 0.75 to 1.40 mm, with females larger than males and possibly visible with the naked eye.^1,2

Two or 3 days after a blood meal, the female mite lays approximately 100 eggs in its nest but not on the surface of a host. The eggs hatch into larvae after 1 to 4 days and go on to complete their life cyle.¹ During developmental stages, mites occupy their hosts for blood meals. Mites search for their hosts at night and prefer wild or pet rodents for blood meals but are not host specific and can be found on many mammals including birds, cats, racoons, and squirrels.⁴

Although tropical rat mites prefer rodent hosts, they can infest humans when their preferred host is unavailable. In the United States, the first case of human dermatitis due to a tropical rate mite occurred in 1923. In Europe, rat mite dermatitis was first reported in a human in 1931, possibly due to contamination of sailing vessels.⁴

Infestation and Transmission

Tropical rat mites prefer wild and pet rodents as hosts because the mites are able to feed on their blood over long periods.⁴ During the day, the mite spends most of its time hiding in dark dry spaces; it is most active during the night, traveling to find a host for meals.^3-5 If a preferred host is not present, the mite may choose to infest a human.⁵

Human infestation occurs most often upon close bodily contact with an infected animal or pet rodent that was sold without parasites having been eliminated.^3-5 Mites are able to survive without a host for as long as 6 months; they may travel after a meal.^1,2 Therefore, individuals who do not have a pet rodent can be infested if an infected wild rodent has infested their living space.^1,3-5

Clinical Presentation of Infestation

Patients infested with tropical rat mites present with pruritic cutaneous lesions, most often on unclothed parts of the body that are easily exposed to mites; lesions rarely occur on the scalp.⁵ People of any age or gender can be infested. Rat mite bites can present as single or grouped, pruritic, erythematous papules ranging in size from 4 to 10 mm in diameter.^5-7 Excoriations may be present due to excessive scratching. Although rare, vesicles or nodules have been reported.^5,7

Diagnosis of the underlying cause of the cutaneous manifestations often is difficult because mites are not visible during the day, as they are less active then.² Lesions often are misdiagnosed as an allergic response, a bacterial infection, or various forms of dermatitis.¹ A parasitic cause often is not considered unless the physician or patient detects a mite or many trials of therapies fail to provide relief.^1,3-5 Eliciting a thorough history may disclose that the patient has had close contact with rodents or lives in a community center, shelter, or shared space. If any of the patient’s close contacts have a similar presentation, infestation with mites should be considered.

Patients should be educated about treatment options and measures that need to be taken to prevent reinfection. It has been reported that tropical rat mites can survive without a blood meal for as long as 6 months; therefore, meticulous inspection and decontamination of all living spaces is required.^1,4 Once identified, physicians may prescribe an antiparasitic such as permethrin or pyriproxyfen to prevent further infestation and eliminate mites on the host.⁵ Lindane and benzyl benzoate previously were reported to be effective but should be prescribed only in correctly diagnosed cases due to the potential adverse effects of both therapies.^4,7-10 For effective treatment, physicians should thoroughly review the proper application of topical treatments with patients. Topical creams should be massaged into the skin from the head to the soles of the feet, covering all creases of the skin and between the fingers and toes. Antiparasitic creams should be left on the skin for 8 to 14 hours, and all members of the household should be examined and treated, if necessary, by a physician. A thorough bath removes tropical rat mites, but preventive measures should be taken to prevent reinfestation.⁴ Antihistamines or glucocorticoids also can be used as symptomatic treatment.^6,8

Avoiding Reinfestation—Preventive measures should be taken to prevent reinfestation, including evaluation by an exterminator for any wild rodents to remove nests and treat the living space with an acaricide.⁵ Insecticides administered by exterminators, including malathion, methyl carbamate, and lindane, also have been reported to be effective for preventing reinfestation.^5,7-9 A veterinarian should be consulted if the patient owns any pets to ensure proper identification of any potential tropical rat mites and treatments that may be necessary for any household pets.¹

Case Report

A 68-year-old man presented to the dermatology outpatient clinic with diffuse pruritus of the skin and scalp. He reported no other symptoms and had never had a total-body skin examination. His primary care physician recently prescribed a dose pack of methylprednisolone 4-mg tablets, which relieved the symptoms except for a mild scalp itch. His wife did not experience itching, and he denied noticing mites or fleas on his pet dog. Physical examination did not reveal any contributory findings, such as erythema or rash. Ketoconazole shampoo 2% and fluocinolone solution 0.01% were prescribed for scalp pruritus; however, he could not afford those medications and therefore did not take them.

Two weeks later, the patient presented with diffuse itching that involved the scalp, trunk, and extremities. He denied groin pruritus. He reported that the itching was worse at night. His wife continued to be asymptomatic. The patient reported that his health screening was up-to-date, and he had no interval health changes. A complete blood cell count, thyroid studies, and a comprehensive metabolic panel performed recently were within reference range. He denied recent travel or taking new medications. Physical examination revealed a somewhat linear distribution of erythematous urticarial papules on the right side of the abdomen. Red dermatographic excoriations were noted on the back. No burrows were visualized. He was given intramuscular triamcinolone 60 mg and was advised to have his house evaluated for bed bugs and his pet dog evaluated by a veterinarian for mites. During the triamcinolone injection, the medical assistant observed a 1- to 2-mm red insect, which fell into his clothing and could not be further evaluated.

After 1 month, the patient had no improvement of the pruritus; instead, it became worse. During this time, his wife developed intermittent urticarial-like eruptions. He was taking oral diphenhydramine nightly and applying triamcinolone cream 0.5% that he had at home from an earlier skin problem as needed. Physical examination findings correlated with worsening symptoms. He had multiple erythematous urticarial papules—many of which were excoriated—across the chest, abdomen, buttocks, and back. The arms had multiple excoriations. The urticarial papules coalesced in the anterior axillary folds, yet no burrows were visualized. In the left anterior axillary fold adjacent to one of the urticarial papules, a 1-mm mobile mite was identified on dermoscopy. Further evaluation by microscopy showed morphologic characteristics of a tropical rat mite (Figure). The patient admitted that his house had a mouse infestation that he was struggling to eliminate. Permethrin cream 5% was prescribed. Because the patient could not afford the prescription, he was advised to use the triamcinolone cream 0.5%and oral diphenhydramine that he had at home nightly for symptomatic relief. He was advised to hire an exterminator to eradicate the mouse and mite infestation to prevent reinfestation.

Identification of Rate Mite Dermatitis

The characteristics of tropical rat mite dermatitis can be confused with many other conditions, such as infection. Even when a mite is identified, it can be difficult to classify it as a tropical rat mite. To confirm the diagnosis of tropical rat mite dermatitis, the parasite needs to be identified. Skin scrapings can be collected from pruritic lesions and examined microscopically in the hope of revealing the rat mites. The recommendation is to collect skin scrapings from the dorsal aspect of the hands or from the neck.⁵ Patients may report finding mites in their living space or on their bedding or clothing.

Although the tropical rat mite was reported as a vector for endemic typhus between humans, no other cases of transmission between humans have been reported since.^11,12 Studies reporting non–human subject research and case reports have shown that O bacoti is a vector for Rickettsia akari, Coxiella burnetii, Francisella tularensis, Yersinia pestis, Eastern equine encephalitis virus (Alphavirus), Enterovirus (Picornaviridae), Langat virus (Flavivirus), and Hantaan orthohantavirus.^5,11-17 However, no cases of these infectious diseases being transmitted naturally have been reported.⁵

Confirmation of O bacoti as a vector for human pathogens is difficult because it relies on identification of the mite in the clinic.⁵ The epidemiologic importance of the mite in transmitting infectious disease is unknown; reports of human cases of mite infestation are rare. We present this information to increase awareness and help dermatologists and other health care providers identify O bacoti.

The Diagnosis: Flagellate Dermatitis

Upon further questioning by dermatology, the patient noted recent ingestion of shiitake mushrooms, which were not a part of his typical diet. Based on the appearance of the rash in the context of ingesting shiitake mushrooms, our patient was diagnosed with flagellate dermatitis. At 6-week followup, the patient’s rash had resolved spontaneously without further intervention.

Flagellate dermatitis usually appears on the torso as linear whiplike streaks.¹ The eruption often is pruritic and may be preceded by severe pruritus. Flagellate dermatitis also is a well-documented complication of bleomycin sulfate therapy with an incidence rate of 8% to 66%.²

Other chemotherapeutic causes include peplomycin, bendamustine, docetaxel, cisplatin, and trastuzumab.³ Flagellate dermatitis also is seen in some patients with dermatomyositis.⁴ A thorough patient history, including medications and dietary habits, is necessary to differentiate flagellate dermatitis from dermatomyositis.

Flagellate dermatitis, also known as shiitake dermatitis, is observed as erythematous flagellate eruptions involving the trunk or extremities that present within 2 hours to 5 days of handling or consuming undercooked or raw shiitake mushrooms (Lentinula edodes),^5,6 as was observed in our patient. Lentinan is the polysaccharide component of the shiitake species and is destabilized by heat.⁶ Ingestion of polysaccharide is associated with dermatitis, particularly in Japan, China, and Korea; however, the consumption of shiitake mushrooms has increased worldwide, and cases increasingly are reported outside of these typical regions. The rash typically resolves spontaneously; therefore, treatment is supportive. However, more severe symptomatic cases may require courses of topical corticosteroids and antihistamines.⁶

In our case, the differential diagnosis consisted of acute urticaria, cutaneous dermatomyositis, dermatographism, and maculopapular cutaneous mastocytosis. Acute urticaria displays well-circumscribed edematous papules or plaques, and individual lesions last less than 24 hours. Cutaneous dermatomyositis includes additional systemic manifestations such as fatigue, malaise, and myalgia, as well as involvement of the gastrointestinal, respiratory, or cardiac organs. Dermatographism is evoked by stroking or rubbing of the skin, which results in asymptomatic lesions that persist for 15 to 30 minutes. Cases of maculopapular cutaneous mastocytosis more often are seen in children, and the histamine release most often causes gastrointestinal tract symptoms such as nausea, vomiting, and diarrhea, as well as flushing, blushing, pruritus, respiratory difficulty, and malaise.

The Diagnosis: Flagellate Dermatitis

Upon further questioning by dermatology, the patient noted recent ingestion of shiitake mushrooms, which were not a part of his typical diet. Based on the appearance of the rash in the context of ingesting shiitake mushrooms, our patient was diagnosed with flagellate dermatitis. At 6-week followup, the patient’s rash had resolved spontaneously without further intervention.

Flagellate dermatitis usually appears on the torso as linear whiplike streaks.¹ The eruption often is pruritic and may be preceded by severe pruritus. Flagellate dermatitis also is a well-documented complication of bleomycin sulfate therapy with an incidence rate of 8% to 66%.²

Other chemotherapeutic causes include peplomycin, bendamustine, docetaxel, cisplatin, and trastuzumab.³ Flagellate dermatitis also is seen in some patients with dermatomyositis.⁴ A thorough patient history, including medications and dietary habits, is necessary to differentiate flagellate dermatitis from dermatomyositis.

Flagellate dermatitis, also known as shiitake dermatitis, is observed as erythematous flagellate eruptions involving the trunk or extremities that present within 2 hours to 5 days of handling or consuming undercooked or raw shiitake mushrooms (Lentinula edodes),^5,6 as was observed in our patient. Lentinan is the polysaccharide component of the shiitake species and is destabilized by heat.⁶ Ingestion of polysaccharide is associated with dermatitis, particularly in Japan, China, and Korea; however, the consumption of shiitake mushrooms has increased worldwide, and cases increasingly are reported outside of these typical regions. The rash typically resolves spontaneously; therefore, treatment is supportive. However, more severe symptomatic cases may require courses of topical corticosteroids and antihistamines.⁶

In our case, the differential diagnosis consisted of acute urticaria, cutaneous dermatomyositis, dermatographism, and maculopapular cutaneous mastocytosis. Acute urticaria displays well-circumscribed edematous papules or plaques, and individual lesions last less than 24 hours. Cutaneous dermatomyositis includes additional systemic manifestations such as fatigue, malaise, and myalgia, as well as involvement of the gastrointestinal, respiratory, or cardiac organs. Dermatographism is evoked by stroking or rubbing of the skin, which results in asymptomatic lesions that persist for 15 to 30 minutes. Cases of maculopapular cutaneous mastocytosis more often are seen in children, and the histamine release most often causes gastrointestinal tract symptoms such as nausea, vomiting, and diarrhea, as well as flushing, blushing, pruritus, respiratory difficulty, and malaise.

The Diagnosis: Flagellate Dermatitis

Upon further questioning by dermatology, the patient noted recent ingestion of shiitake mushrooms, which were not a part of his typical diet. Based on the appearance of the rash in the context of ingesting shiitake mushrooms, our patient was diagnosed with flagellate dermatitis. At 6-week followup, the patient’s rash had resolved spontaneously without further intervention.

Flagellate dermatitis usually appears on the torso as linear whiplike streaks.¹ The eruption often is pruritic and may be preceded by severe pruritus. Flagellate dermatitis also is a well-documented complication of bleomycin sulfate therapy with an incidence rate of 8% to 66%.²

Other chemotherapeutic causes include peplomycin, bendamustine, docetaxel, cisplatin, and trastuzumab.³ Flagellate dermatitis also is seen in some patients with dermatomyositis.⁴ A thorough patient history, including medications and dietary habits, is necessary to differentiate flagellate dermatitis from dermatomyositis.

Flagellate dermatitis, also known as shiitake dermatitis, is observed as erythematous flagellate eruptions involving the trunk or extremities that present within 2 hours to 5 days of handling or consuming undercooked or raw shiitake mushrooms (Lentinula edodes),^5,6 as was observed in our patient. Lentinan is the polysaccharide component of the shiitake species and is destabilized by heat.⁶ Ingestion of polysaccharide is associated with dermatitis, particularly in Japan, China, and Korea; however, the consumption of shiitake mushrooms has increased worldwide, and cases increasingly are reported outside of these typical regions. The rash typically resolves spontaneously; therefore, treatment is supportive. However, more severe symptomatic cases may require courses of topical corticosteroids and antihistamines.⁶

In our case, the differential diagnosis consisted of acute urticaria, cutaneous dermatomyositis, dermatographism, and maculopapular cutaneous mastocytosis. Acute urticaria displays well-circumscribed edematous papules or plaques, and individual lesions last less than 24 hours. Cutaneous dermatomyositis includes additional systemic manifestations such as fatigue, malaise, and myalgia, as well as involvement of the gastrointestinal, respiratory, or cardiac organs. Dermatographism is evoked by stroking or rubbing of the skin, which results in asymptomatic lesions that persist for 15 to 30 minutes. Cases of maculopapular cutaneous mastocytosis more often are seen in children, and the histamine release most often causes gastrointestinal tract symptoms such as nausea, vomiting, and diarrhea, as well as flushing, blushing, pruritus, respiratory difficulty, and malaise.

Clinicians are using dupilumab off label to treat a wider range of allergic conditions in adults and children.

The drug, marketed as Dupixent, is currently approved in the United States to treat atopic dermatitis, asthma, chronic rhinosinusitis with nasal polyposis, eosinophilic esophagitis, and prurigo nodularis in adults. Dupilumab is also approved to treat eosinophilic esophagitis in patients aged 12 years and older and atopic dermatitis and asthma in some patients as young as age 6 months.

As the roster of approved and off-label indications grows, skin specialists said, pediatricians and other primary care providers should become familiar with the drug – given the increasing likelihood that their patients may be taking the medication.

The U.S. Food and Drug Administration first approved dupilumab in 2017 for eczema and has continued to add new treatment indications, the most recent being for prurigo nodularis, in 2022. Sanofi, which markets the drug with Regeneron, announced in April 2022 that some 430,000 patients worldwide were taking the drug – a figure it hoped to raise by 1.5 million by 2025.
 

A well-tolerated – if expensive – drug

Dupilumab, an interleukin-4 (IL-4) receptor alpha-antagonist biologic, blocks both IL-4 and IL-13 signaling, Marlys Fassett, MD, PhD, associate professor of dermatology at the University of California, San Francisco, told this news organization.

Dr. Fassett said she prescribes the drug off label for chronic idiopathic urticaria, including in older patients, and finds that the side effects in older patients are similar to those in younger people. The medication costs $36,000 per year, although some patients can get it more cheaply.

“Dupixent is a super-safe drug because it doesn’t immunosuppress any other part of the immune system, so you still have good antibacterial, antiviral, and antifungal immunity,” she added. “That makes perfect sense as a biological mechanism, and it’s been found safe in clinical trials.”

Case reports of potential adverse reactions to dupilumab have included ocular surface disease, lichen planus, and rash on the face and neck.

“We’re still learning about complications and are watching patients carefully,” said Marissa J. Perman, MD, section chief of dermatology at Children’s Hospital of Philadelphia.

Many people with atopic dermatitis also have other allergic conditions, such as contact dermatitis, asthma, prurigo nodularis, allergic rhinitis, and seasonal allergies. Each of these conditions has a pathway that depends on IL-4 receptors, Dr. Fassett said.

“It’s amazing how many conditions Dupixent improves. Sometimes we prescribe on-label Dupixent for atopic dermatitis, and inadvertently, the drug also improves that patient’s other, off-label conditions,” Dr. Fassett said. “I think that’s the best evidence that Dupixent works in these off-label cases.”

Lindsay C. Strowd, MD, associate professor of dermatology at Wake Forest University, Winston-Salem, N.C., said she uses off-label dupilumab to treat bullous pemphigoid and intense pruritus of unknown etiology.

“And several times I have treated drug reaction with eosinophilia and systemic symptoms, a rare adverse drug reaction that causes a rash and eosinophilia,” Dr. Strowd added.

Tissa Hata, MD, professor of medicine and clinical service chief at the University of California, San Diego, mainly treats elderly patients. She uses dupilumab to treat bullous pemphigoid and chronic pruritus. “There have been reports of using Dupixent to treat adult alopecia areata, chronic urticaria, localized scleroderma, and even keloids,” she told this news organization.

As a pediatric dermatologist, Dr. Perman treats children with atopic dermatitis as young as 3 months of age. She also uses dupilumab for alopecia areata, graft vs. host disease, and pruritus not otherwise specified.

Conjunctivitis and facial redness are two side effects Dr. Fassett sometimes sees with dupilumab. They occur similarly with all conditions and in all age groups. “We don’t know why they occur, and we don’t always know how to alleviate them,” she said. “So a small number of patients stop using Dupixent because they can’t tolerate those two side effects.

“We’re not worried about infection risk,” Dr. Fassett said. “Your patients may have heard of dupilumab as an immunosuppressant, but its immunosuppression is very focused. You can reassure them that they’re not at increased risk for viral or bacterial infections when they’re on this drug.”

“I don’t think there are any different safety signals to watch for with on-label vs. off-label Dupixent use,” Dr. Strowd added. “In general, the medicine is very safe.”

Dr. Hata said she is impressed with dupilumab’s safety in her elderly patients. All her patients older than 85 years who have taken the drug for bullous pemphigoid have tolerated it well, she said.

“Dupixent seems to be a safe alternative for elderly patients with pruritus because they often cannot tolerate sedating antihistamines due to the risk of falling,” Dr. Hata said. “And UV therapy may be difficult for elderly patients due to problems with transport.”

Although some of Dr. Hata’s elderly patients with atopic dermatitis have discontinued use of the drug after developing conjunctivitis, none taking the drug off label have discontinued it because of side effects, she noted.

“Dupixent manages the condition, but it is not a cure,” Dr. Fassett noted. “Based on the current data, we think it’s safe and effective to take long term, potentially for life.”

Making injections less bothersome

Dupilumab is injected subcutaneously from a single-dose prefilled syringe or a prefilled pen (syringe hidden in an opaque sheath), typically in the thigh, arm, abdomen, or buttocks. According to Sanofi and Regeneron, patients receive dupilumab injections every 2 to 4 weeks in doses based on their age and weight.

“The medication is somewhat viscous, so taking the syringe or pen out of the refrigerator ahead of time to warm it up can make the experience less painful,” Dr. Strowd advised. “For pediatric patients, I sometimes prescribe topical lidocaine applied 30 minutes before injection.”

Dr. Hata suggested icing the skin prior to injecting or distracting the patient by tapping a different area of the skin.

For her pediatric patients, Dr. Perman said she uses “lots of distraction, EMLA cream, and having one person hold the child while a second person injects.”

Clinic and pharmacy staff may show patients how to inject properly, Dr. Fassett added; and the product website provides injection tutorials.
 

Off-label dupixent can be expensive, difficult to obtain

The list price per injection, regardless of dose, is around $1,800. But according to the company’s website, most patients have health insurance or qualify for other assistance, so “very few patients pay the list price.”

Even so, “due to cost and insurance coverage hurdles, obtaining Dupixent for off-label use can be difficult,” Dr. Strowd said.

“In academic medicine, we can obtain drugs for our patients that community doctors may not get approval for,” Dr. Fassett added. “Community doctors can use information in the medical literature and in news articles to press insurance companies to spend money to provide their patients with Dupixent.”

The experts who commented have disclosed no relevant financial relationships.

A version of this article appeared on Medscape.com.

Clinicians are using dupilumab off label to treat a wider range of allergic conditions in adults and children.

The drug, marketed as Dupixent, is currently approved in the United States to treat atopic dermatitis, asthma, chronic rhinosinusitis with nasal polyposis, eosinophilic esophagitis, and prurigo nodularis in adults. Dupilumab is also approved to treat eosinophilic esophagitis in patients aged 12 years and older and atopic dermatitis and asthma in some patients as young as age 6 months.

As the roster of approved and off-label indications grows, skin specialists said, pediatricians and other primary care providers should become familiar with the drug – given the increasing likelihood that their patients may be taking the medication.

The U.S. Food and Drug Administration first approved dupilumab in 2017 for eczema and has continued to add new treatment indications, the most recent being for prurigo nodularis, in 2022. Sanofi, which markets the drug with Regeneron, announced in April 2022 that some 430,000 patients worldwide were taking the drug – a figure it hoped to raise by 1.5 million by 2025.
 

A well-tolerated – if expensive – drug

Dupilumab, an interleukin-4 (IL-4) receptor alpha-antagonist biologic, blocks both IL-4 and IL-13 signaling, Marlys Fassett, MD, PhD, associate professor of dermatology at the University of California, San Francisco, told this news organization.

Dr. Fassett said she prescribes the drug off label for chronic idiopathic urticaria, including in older patients, and finds that the side effects in older patients are similar to those in younger people. The medication costs $36,000 per year, although some patients can get it more cheaply.

“Dupixent is a super-safe drug because it doesn’t immunosuppress any other part of the immune system, so you still have good antibacterial, antiviral, and antifungal immunity,” she added. “That makes perfect sense as a biological mechanism, and it’s been found safe in clinical trials.”

Case reports of potential adverse reactions to dupilumab have included ocular surface disease, lichen planus, and rash on the face and neck.

“We’re still learning about complications and are watching patients carefully,” said Marissa J. Perman, MD, section chief of dermatology at Children’s Hospital of Philadelphia.

Many people with atopic dermatitis also have other allergic conditions, such as contact dermatitis, asthma, prurigo nodularis, allergic rhinitis, and seasonal allergies. Each of these conditions has a pathway that depends on IL-4 receptors, Dr. Fassett said.

“It’s amazing how many conditions Dupixent improves. Sometimes we prescribe on-label Dupixent for atopic dermatitis, and inadvertently, the drug also improves that patient’s other, off-label conditions,” Dr. Fassett said. “I think that’s the best evidence that Dupixent works in these off-label cases.”

Lindsay C. Strowd, MD, associate professor of dermatology at Wake Forest University, Winston-Salem, N.C., said she uses off-label dupilumab to treat bullous pemphigoid and intense pruritus of unknown etiology.

“And several times I have treated drug reaction with eosinophilia and systemic symptoms, a rare adverse drug reaction that causes a rash and eosinophilia,” Dr. Strowd added.

Tissa Hata, MD, professor of medicine and clinical service chief at the University of California, San Diego, mainly treats elderly patients. She uses dupilumab to treat bullous pemphigoid and chronic pruritus. “There have been reports of using Dupixent to treat adult alopecia areata, chronic urticaria, localized scleroderma, and even keloids,” she told this news organization.

As a pediatric dermatologist, Dr. Perman treats children with atopic dermatitis as young as 3 months of age. She also uses dupilumab for alopecia areata, graft vs. host disease, and pruritus not otherwise specified.

Conjunctivitis and facial redness are two side effects Dr. Fassett sometimes sees with dupilumab. They occur similarly with all conditions and in all age groups. “We don’t know why they occur, and we don’t always know how to alleviate them,” she said. “So a small number of patients stop using Dupixent because they can’t tolerate those two side effects.

“We’re not worried about infection risk,” Dr. Fassett said. “Your patients may have heard of dupilumab as an immunosuppressant, but its immunosuppression is very focused. You can reassure them that they’re not at increased risk for viral or bacterial infections when they’re on this drug.”

“I don’t think there are any different safety signals to watch for with on-label vs. off-label Dupixent use,” Dr. Strowd added. “In general, the medicine is very safe.”

Dr. Hata said she is impressed with dupilumab’s safety in her elderly patients. All her patients older than 85 years who have taken the drug for bullous pemphigoid have tolerated it well, she said.

“Dupixent seems to be a safe alternative for elderly patients with pruritus because they often cannot tolerate sedating antihistamines due to the risk of falling,” Dr. Hata said. “And UV therapy may be difficult for elderly patients due to problems with transport.”

Although some of Dr. Hata’s elderly patients with atopic dermatitis have discontinued use of the drug after developing conjunctivitis, none taking the drug off label have discontinued it because of side effects, she noted.

“Dupixent manages the condition, but it is not a cure,” Dr. Fassett noted. “Based on the current data, we think it’s safe and effective to take long term, potentially for life.”

Making injections less bothersome

Dupilumab is injected subcutaneously from a single-dose prefilled syringe or a prefilled pen (syringe hidden in an opaque sheath), typically in the thigh, arm, abdomen, or buttocks. According to Sanofi and Regeneron, patients receive dupilumab injections every 2 to 4 weeks in doses based on their age and weight.

“The medication is somewhat viscous, so taking the syringe or pen out of the refrigerator ahead of time to warm it up can make the experience less painful,” Dr. Strowd advised. “For pediatric patients, I sometimes prescribe topical lidocaine applied 30 minutes before injection.”

Dr. Hata suggested icing the skin prior to injecting or distracting the patient by tapping a different area of the skin.

For her pediatric patients, Dr. Perman said she uses “lots of distraction, EMLA cream, and having one person hold the child while a second person injects.”

Clinic and pharmacy staff may show patients how to inject properly, Dr. Fassett added; and the product website provides injection tutorials.
 

Off-label dupixent can be expensive, difficult to obtain

The list price per injection, regardless of dose, is around $1,800. But according to the company’s website, most patients have health insurance or qualify for other assistance, so “very few patients pay the list price.”

Even so, “due to cost and insurance coverage hurdles, obtaining Dupixent for off-label use can be difficult,” Dr. Strowd said.

“In academic medicine, we can obtain drugs for our patients that community doctors may not get approval for,” Dr. Fassett added. “Community doctors can use information in the medical literature and in news articles to press insurance companies to spend money to provide their patients with Dupixent.”

The experts who commented have disclosed no relevant financial relationships.

A version of this article appeared on Medscape.com.

Clinicians are using dupilumab off label to treat a wider range of allergic conditions in adults and children.

The drug, marketed as Dupixent, is currently approved in the United States to treat atopic dermatitis, asthma, chronic rhinosinusitis with nasal polyposis, eosinophilic esophagitis, and prurigo nodularis in adults. Dupilumab is also approved to treat eosinophilic esophagitis in patients aged 12 years and older and atopic dermatitis and asthma in some patients as young as age 6 months.

As the roster of approved and off-label indications grows, skin specialists said, pediatricians and other primary care providers should become familiar with the drug – given the increasing likelihood that their patients may be taking the medication.

The U.S. Food and Drug Administration first approved dupilumab in 2017 for eczema and has continued to add new treatment indications, the most recent being for prurigo nodularis, in 2022. Sanofi, which markets the drug with Regeneron, announced in April 2022 that some 430,000 patients worldwide were taking the drug – a figure it hoped to raise by 1.5 million by 2025.
 

A well-tolerated – if expensive – drug

Dupilumab, an interleukin-4 (IL-4) receptor alpha-antagonist biologic, blocks both IL-4 and IL-13 signaling, Marlys Fassett, MD, PhD, associate professor of dermatology at the University of California, San Francisco, told this news organization.

Dr. Fassett said she prescribes the drug off label for chronic idiopathic urticaria, including in older patients, and finds that the side effects in older patients are similar to those in younger people. The medication costs $36,000 per year, although some patients can get it more cheaply.

“Dupixent is a super-safe drug because it doesn’t immunosuppress any other part of the immune system, so you still have good antibacterial, antiviral, and antifungal immunity,” she added. “That makes perfect sense as a biological mechanism, and it’s been found safe in clinical trials.”

Case reports of potential adverse reactions to dupilumab have included ocular surface disease, lichen planus, and rash on the face and neck.

“We’re still learning about complications and are watching patients carefully,” said Marissa J. Perman, MD, section chief of dermatology at Children’s Hospital of Philadelphia.

Many people with atopic dermatitis also have other allergic conditions, such as contact dermatitis, asthma, prurigo nodularis, allergic rhinitis, and seasonal allergies. Each of these conditions has a pathway that depends on IL-4 receptors, Dr. Fassett said.

“It’s amazing how many conditions Dupixent improves. Sometimes we prescribe on-label Dupixent for atopic dermatitis, and inadvertently, the drug also improves that patient’s other, off-label conditions,” Dr. Fassett said. “I think that’s the best evidence that Dupixent works in these off-label cases.”

Lindsay C. Strowd, MD, associate professor of dermatology at Wake Forest University, Winston-Salem, N.C., said she uses off-label dupilumab to treat bullous pemphigoid and intense pruritus of unknown etiology.

“And several times I have treated drug reaction with eosinophilia and systemic symptoms, a rare adverse drug reaction that causes a rash and eosinophilia,” Dr. Strowd added.

Tissa Hata, MD, professor of medicine and clinical service chief at the University of California, San Diego, mainly treats elderly patients. She uses dupilumab to treat bullous pemphigoid and chronic pruritus. “There have been reports of using Dupixent to treat adult alopecia areata, chronic urticaria, localized scleroderma, and even keloids,” she told this news organization.

As a pediatric dermatologist, Dr. Perman treats children with atopic dermatitis as young as 3 months of age. She also uses dupilumab for alopecia areata, graft vs. host disease, and pruritus not otherwise specified.

Conjunctivitis and facial redness are two side effects Dr. Fassett sometimes sees with dupilumab. They occur similarly with all conditions and in all age groups. “We don’t know why they occur, and we don’t always know how to alleviate them,” she said. “So a small number of patients stop using Dupixent because they can’t tolerate those two side effects.

“We’re not worried about infection risk,” Dr. Fassett said. “Your patients may have heard of dupilumab as an immunosuppressant, but its immunosuppression is very focused. You can reassure them that they’re not at increased risk for viral or bacterial infections when they’re on this drug.”

“I don’t think there are any different safety signals to watch for with on-label vs. off-label Dupixent use,” Dr. Strowd added. “In general, the medicine is very safe.”

Dr. Hata said she is impressed with dupilumab’s safety in her elderly patients. All her patients older than 85 years who have taken the drug for bullous pemphigoid have tolerated it well, she said.

“Dupixent seems to be a safe alternative for elderly patients with pruritus because they often cannot tolerate sedating antihistamines due to the risk of falling,” Dr. Hata said. “And UV therapy may be difficult for elderly patients due to problems with transport.”

Although some of Dr. Hata’s elderly patients with atopic dermatitis have discontinued use of the drug after developing conjunctivitis, none taking the drug off label have discontinued it because of side effects, she noted.

“Dupixent manages the condition, but it is not a cure,” Dr. Fassett noted. “Based on the current data, we think it’s safe and effective to take long term, potentially for life.”

Making injections less bothersome

Dupilumab is injected subcutaneously from a single-dose prefilled syringe or a prefilled pen (syringe hidden in an opaque sheath), typically in the thigh, arm, abdomen, or buttocks. According to Sanofi and Regeneron, patients receive dupilumab injections every 2 to 4 weeks in doses based on their age and weight.

“The medication is somewhat viscous, so taking the syringe or pen out of the refrigerator ahead of time to warm it up can make the experience less painful,” Dr. Strowd advised. “For pediatric patients, I sometimes prescribe topical lidocaine applied 30 minutes before injection.”

Dr. Hata suggested icing the skin prior to injecting or distracting the patient by tapping a different area of the skin.

For her pediatric patients, Dr. Perman said she uses “lots of distraction, EMLA cream, and having one person hold the child while a second person injects.”

Clinic and pharmacy staff may show patients how to inject properly, Dr. Fassett added; and the product website provides injection tutorials.
 

Off-label dupixent can be expensive, difficult to obtain

The list price per injection, regardless of dose, is around $1,800. But according to the company’s website, most patients have health insurance or qualify for other assistance, so “very few patients pay the list price.”

Even so, “due to cost and insurance coverage hurdles, obtaining Dupixent for off-label use can be difficult,” Dr. Strowd said.

“In academic medicine, we can obtain drugs for our patients that community doctors may not get approval for,” Dr. Fassett added. “Community doctors can use information in the medical literature and in news articles to press insurance companies to spend money to provide their patients with Dupixent.”

The experts who commented have disclosed no relevant financial relationships.

A version of this article appeared on Medscape.com.

Lanolin was announced as the Allergen of the Year by the American Contact Dermatitis Society in March 2023.¹ However, allergic contact dermatitis (ACD) to lanolin remains a matter of fierce debate among dermatologists. Herein, we discuss this important contact allergen, emphasizing the controversy behind its allergenicity and nuances to consider when patch testing.

What is Lanolin?

Lanolin is a greasy, yellow, fatlike substance derived from the sebaceous glands of sheep. It is extracted from wool using an intricate process of scouring with dilute alkali, centrifuging, and refining with hot alkali and bleach.² It is comprised of a complex mixture of esters, alcohols, sterols, fatty acids, lactose, and hydrocarbons.³

The hydrophobic property of lanolin helps sheep shed water from their coats.³ In humans, this hydrophobicity benefits the skin by retaining moisture already present in the epidermis. Lanolin can hold as much as twice its weight in water and may reduce transepidermal water loss by 20% to 30%.^4-6 In addition, lanolin maintains tissue breathability, which supports proper gas exchange, promoting wound healing and protecting against infection.^3,7

Many personal care products (PCPs), cosmetics, and topical medicaments contain lanolin, particularly products marketed to help restore dry cracked skin. The range of permitted concentrations of lanolin in over-the-counter products in the United States is 12.5% to 50%.³ Lanolin also may be found in industrial goods. The Table provides a comprehensive list of common items that may contain lanolin.^1,3,8,9

A Wolf in Sheep’s Clothing?

Despite its benefits, lanolin is a potential source of ACD. The first reported positive patch test (PPT) to lanolin worldwide was in the late 1920s.¹⁰ Subsequent cases of ACD to lanolin were described over the next 30 years, reaching a peak of recognition in the latter half of the 20th century with rates of PPT ranging from 0% to 7.4%, though the patient population and lanolin patch-test formulation used differed across studies.⁹ The North American Contact Dermatitis Group observed that 3.3% (1431/43,691) of patients tested from 2001 to 2018 had a PPT to either lanolin alcohol 30% in petrolatum (pet) or Amerchol L101 (10% lanolin alcohol dissolved in mineral oil) 50% pet.¹¹ Compared to patients referred for patch testing, the prevalence of contact allergy to lanolin is lower in the general population; 0.4% of the general population in Europe (N=3119) tested positive to wool alcohols 1.0 mg/cm² on the thin-layer rapid use Epicutaneous (TRUE) test.¹²

Allergic contact dermatitis to lanolin is unrelated to an allergy to wool itself, which probably does not exist, though wool is well known to cause irritant contact dermatitis, particularly in atopic individuals.¹³

Who Is at Risk for Lanolin Allergy?

In a recent comprehensive review of lanolin allergy, Jenkins and Belsito¹ summarized 4 high-risk subgroups of patients for the development of lanolin contact allergy: stasis dermatitis, chronic leg ulcers, atopic dermatitis (AD), and perianal/genital dermatitis. These chronic inflammatory skin conditions may increase the risk for ACD to lanolin via increased exposure in topical therapies and/or increased allergen penetration through an impaired epidermal barrier.^14-16 Demographically, older adults and children are at-risk groups, likely secondary to the higher prevalence of stasis dermatitis/leg ulcers in the former group and AD in the latter.¹

The allergenicity of lanolin is far from straightforward. In 1996, Wolf¹⁷ first described the “lanolin paradox,” modeled after the earlier “paraben paradox” described by Fisher.¹⁸ There are 4 clinical phenomena of the lanolin paradox¹⁷:

• Lanolin generally does not cause contact allergy when found in PCPs but may cause ACD when found in topical medicaments.
• Some patients can use lanolin-containing PCPs on healthy skin without issue but will develop ACD when a lanolin-containing topical medicament is applied to inflamed skin. This is because inflamed skin is more easily sensitized.
• False-negative patch test reactions to pure lanolin may occur. Since Wolf’s¹⁷ initial description of the paradox, free alcohols of lanolin have been found to be its principal allergen, though it also is possible that oxidation of lanolin could generate additional allergenic substances.¹
• Patch testing with wool alcohol 30% can generate both false-negative and false-positive results.

At one extreme, Kligman¹⁹ also was concerned about false-positive reactions to lanolin, describing lanolin allergy as a myth attributed to overzealous patch testing and a failure to appreciate the limitations of this diagnostic modality. Indeed, just having a PPT to lanolin (ie, contact allergy) does not automatically translate to a relevant ACD,¹ and determining the clinical relevance of a PPT is of utmost importance. In 2001, Wakelin et al²⁰ reported that the majority (71% [92/130]) of positive reactions to Amerchol L101 50% or 100% pet showed current clinical relevance. Data from the North American Contact Dermatitis Group in 2009 and in 2022 were similar, with 83.4% (529/634) of positive reactions to lanolin alcohol 30% pet and 86.5% (1238/1431) of positive reactions to Amerchol L101 50% pet classified as current clinical relevance.^11,21 These findings demonstrate that although lanolin may be a weak sensitizer, a PPT usually represents a highly relevant cause of dermatitis.

Considerations for Patch Testing

Considering Wolf’s¹⁷ claim that even pure lanolin is not an appropriate formulation to use for patch testing due to the risk for inaccurate results, you might now be wondering which preparation should be used. Mortensen²² popularized another compound, Amerchol L101, in 1979. In this small study of 60 patients with a PPT to lanolin and/or its derivatives, the highest proportion (37% [22/60]) were positive to Amerchol L101 but negative to wool alcohol 30%, suggesting the need to test to more than one preparation simultaneously.²² In a larger study by Miest et al,²³ 3.9% (11/268) of patients had a PPT to Amerchol L101 50% pet, whereas only 1.1% (3/268) had a PPT to lanolin alcohol 30% pet. This highlighted the importance of including Amerchol L101 when patch testing because it was thought to capture more positive results; however, some studies suggest that Amerchol L101 is not superior at predicting lanolin contact allergy vs lanolin alcohol 30% pet. The risk for an irritant reaction when patch testing with Amerchol L101 should be considered due to its mineral oil component.²⁴

Although there is no universal consensus to date, some investigators suggest patch testing both lanolin alcohol 30% pet and Amerchol L101 50% pet simultaneously.¹ The TRUE test utilizes 1000 µg/cm² of wool alcohols, while the North American 80 Comprehensive Series and the American Contact Dermatitis Society Core 90 Series contain Amerchol L101 50% pet. Patch testing to the most allergenic component of lanolin—the free fatty alcohols (particularly alkane-α,β-diols and alkane-α,ω-diols)—has been suggested,¹ though these formulations are not yet commercially available.

When available, the patient’s own lanolin-containing PCPs should be tested.¹ Performing a repeat open application test (ROAT) to a lanolin-containing product also may be highly useful to distinguish weak-positive from irritant patch test reactions and to determine if sensitized patients can tolerate lanolin-containing products on intact skin. To complete a ROAT, a patient should apply the suspected leave-on product to a patch of unaffected skin (classically the volar forearm) twice daily for at least 10 days.²⁵ If the application site is clear after 10 days, the patient is unlikely to have ACD to the product in question. Compared to patch testing, ROAT more accurately mimics a true use situation, which is particularly important for lanolin given its tendency to preferentially impact damaged or inflamed skin while sparing healthy skin.

Alternatives to Lanolin

Patients with confirmed ACD to lanolin may use plain petrolatum, a safe and inexpensive substitute with equivalent moisturizing efficacy. It can reduce transepidermal water loss by more than 98%,⁴ with essentially no risk for ACD. Humectants such as glycerin, sorbitol, and α-hydroxy acids also have moisturizing properties akin to those of lanolin. In addition, some oils may provide benefit to patients with chronic skin conditions. Sunflower seed oil and extra virgin coconut oil have anti-inflammatory, antibacterial, and barrier repair properties.^26,27 Allergic contact dermatitis to these oils rarely, if ever, occurs.²⁸

Final Interpretation

Lanolin is a well-known yet controversial contact allergen that is widely used in PCPs, cosmetics, topical medicaments, and industrial goods. Lanolin ACD preferentially impacts patients with stasis dermatitis, chronic leg ulcers, AD, and perianal/genital dermatitis. Patch testing with more than one lanolin formulation, including lanolin alcohol 30% pet and/or Amerchol L101 50% pet, as well as testing the patient’s own products may be necessary to confirm the diagnosis. In cases of ACD to lanolin, an alternative agent, such as plain petrolatum, may be used.

Lanolin was announced as the Allergen of the Year by the American Contact Dermatitis Society in March 2023.¹ However, allergic contact dermatitis (ACD) to lanolin remains a matter of fierce debate among dermatologists. Herein, we discuss this important contact allergen, emphasizing the controversy behind its allergenicity and nuances to consider when patch testing.

What is Lanolin?

Lanolin is a greasy, yellow, fatlike substance derived from the sebaceous glands of sheep. It is extracted from wool using an intricate process of scouring with dilute alkali, centrifuging, and refining with hot alkali and bleach.² It is comprised of a complex mixture of esters, alcohols, sterols, fatty acids, lactose, and hydrocarbons.³

The hydrophobic property of lanolin helps sheep shed water from their coats.³ In humans, this hydrophobicity benefits the skin by retaining moisture already present in the epidermis. Lanolin can hold as much as twice its weight in water and may reduce transepidermal water loss by 20% to 30%.^4-6 In addition, lanolin maintains tissue breathability, which supports proper gas exchange, promoting wound healing and protecting against infection.^3,7

Many personal care products (PCPs), cosmetics, and topical medicaments contain lanolin, particularly products marketed to help restore dry cracked skin. The range of permitted concentrations of lanolin in over-the-counter products in the United States is 12.5% to 50%.³ Lanolin also may be found in industrial goods. The Table provides a comprehensive list of common items that may contain lanolin.^1,3,8,9

A Wolf in Sheep’s Clothing?

Despite its benefits, lanolin is a potential source of ACD. The first reported positive patch test (PPT) to lanolin worldwide was in the late 1920s.¹⁰ Subsequent cases of ACD to lanolin were described over the next 30 years, reaching a peak of recognition in the latter half of the 20th century with rates of PPT ranging from 0% to 7.4%, though the patient population and lanolin patch-test formulation used differed across studies.⁹ The North American Contact Dermatitis Group observed that 3.3% (1431/43,691) of patients tested from 2001 to 2018 had a PPT to either lanolin alcohol 30% in petrolatum (pet) or Amerchol L101 (10% lanolin alcohol dissolved in mineral oil) 50% pet.¹¹ Compared to patients referred for patch testing, the prevalence of contact allergy to lanolin is lower in the general population; 0.4% of the general population in Europe (N=3119) tested positive to wool alcohols 1.0 mg/cm² on the thin-layer rapid use Epicutaneous (TRUE) test.¹²

Allergic contact dermatitis to lanolin is unrelated to an allergy to wool itself, which probably does not exist, though wool is well known to cause irritant contact dermatitis, particularly in atopic individuals.¹³

Who Is at Risk for Lanolin Allergy?

In a recent comprehensive review of lanolin allergy, Jenkins and Belsito¹ summarized 4 high-risk subgroups of patients for the development of lanolin contact allergy: stasis dermatitis, chronic leg ulcers, atopic dermatitis (AD), and perianal/genital dermatitis. These chronic inflammatory skin conditions may increase the risk for ACD to lanolin via increased exposure in topical therapies and/or increased allergen penetration through an impaired epidermal barrier.^14-16 Demographically, older adults and children are at-risk groups, likely secondary to the higher prevalence of stasis dermatitis/leg ulcers in the former group and AD in the latter.¹

The allergenicity of lanolin is far from straightforward. In 1996, Wolf¹⁷ first described the “lanolin paradox,” modeled after the earlier “paraben paradox” described by Fisher.¹⁸ There are 4 clinical phenomena of the lanolin paradox¹⁷:

• Lanolin generally does not cause contact allergy when found in PCPs but may cause ACD when found in topical medicaments.
• Some patients can use lanolin-containing PCPs on healthy skin without issue but will develop ACD when a lanolin-containing topical medicament is applied to inflamed skin. This is because inflamed skin is more easily sensitized.
• False-negative patch test reactions to pure lanolin may occur. Since Wolf’s¹⁷ initial description of the paradox, free alcohols of lanolin have been found to be its principal allergen, though it also is possible that oxidation of lanolin could generate additional allergenic substances.¹
• Patch testing with wool alcohol 30% can generate both false-negative and false-positive results.

At one extreme, Kligman¹⁹ also was concerned about false-positive reactions to lanolin, describing lanolin allergy as a myth attributed to overzealous patch testing and a failure to appreciate the limitations of this diagnostic modality. Indeed, just having a PPT to lanolin (ie, contact allergy) does not automatically translate to a relevant ACD,¹ and determining the clinical relevance of a PPT is of utmost importance. In 2001, Wakelin et al²⁰ reported that the majority (71% [92/130]) of positive reactions to Amerchol L101 50% or 100% pet showed current clinical relevance. Data from the North American Contact Dermatitis Group in 2009 and in 2022 were similar, with 83.4% (529/634) of positive reactions to lanolin alcohol 30% pet and 86.5% (1238/1431) of positive reactions to Amerchol L101 50% pet classified as current clinical relevance.^11,21 These findings demonstrate that although lanolin may be a weak sensitizer, a PPT usually represents a highly relevant cause of dermatitis.

Considerations for Patch Testing

Considering Wolf’s¹⁷ claim that even pure lanolin is not an appropriate formulation to use for patch testing due to the risk for inaccurate results, you might now be wondering which preparation should be used. Mortensen²² popularized another compound, Amerchol L101, in 1979. In this small study of 60 patients with a PPT to lanolin and/or its derivatives, the highest proportion (37% [22/60]) were positive to Amerchol L101 but negative to wool alcohol 30%, suggesting the need to test to more than one preparation simultaneously.²² In a larger study by Miest et al,²³ 3.9% (11/268) of patients had a PPT to Amerchol L101 50% pet, whereas only 1.1% (3/268) had a PPT to lanolin alcohol 30% pet. This highlighted the importance of including Amerchol L101 when patch testing because it was thought to capture more positive results; however, some studies suggest that Amerchol L101 is not superior at predicting lanolin contact allergy vs lanolin alcohol 30% pet. The risk for an irritant reaction when patch testing with Amerchol L101 should be considered due to its mineral oil component.²⁴

Although there is no universal consensus to date, some investigators suggest patch testing both lanolin alcohol 30% pet and Amerchol L101 50% pet simultaneously.¹ The TRUE test utilizes 1000 µg/cm² of wool alcohols, while the North American 80 Comprehensive Series and the American Contact Dermatitis Society Core 90 Series contain Amerchol L101 50% pet. Patch testing to the most allergenic component of lanolin—the free fatty alcohols (particularly alkane-α,β-diols and alkane-α,ω-diols)—has been suggested,¹ though these formulations are not yet commercially available.

When available, the patient’s own lanolin-containing PCPs should be tested.¹ Performing a repeat open application test (ROAT) to a lanolin-containing product also may be highly useful to distinguish weak-positive from irritant patch test reactions and to determine if sensitized patients can tolerate lanolin-containing products on intact skin. To complete a ROAT, a patient should apply the suspected leave-on product to a patch of unaffected skin (classically the volar forearm) twice daily for at least 10 days.²⁵ If the application site is clear after 10 days, the patient is unlikely to have ACD to the product in question. Compared to patch testing, ROAT more accurately mimics a true use situation, which is particularly important for lanolin given its tendency to preferentially impact damaged or inflamed skin while sparing healthy skin.

Alternatives to Lanolin

Patients with confirmed ACD to lanolin may use plain petrolatum, a safe and inexpensive substitute with equivalent moisturizing efficacy. It can reduce transepidermal water loss by more than 98%,⁴ with essentially no risk for ACD. Humectants such as glycerin, sorbitol, and α-hydroxy acids also have moisturizing properties akin to those of lanolin. In addition, some oils may provide benefit to patients with chronic skin conditions. Sunflower seed oil and extra virgin coconut oil have anti-inflammatory, antibacterial, and barrier repair properties.^26,27 Allergic contact dermatitis to these oils rarely, if ever, occurs.²⁸

Final Interpretation

Lanolin is a well-known yet controversial contact allergen that is widely used in PCPs, cosmetics, topical medicaments, and industrial goods. Lanolin ACD preferentially impacts patients with stasis dermatitis, chronic leg ulcers, AD, and perianal/genital dermatitis. Patch testing with more than one lanolin formulation, including lanolin alcohol 30% pet and/or Amerchol L101 50% pet, as well as testing the patient’s own products may be necessary to confirm the diagnosis. In cases of ACD to lanolin, an alternative agent, such as plain petrolatum, may be used.

Lanolin was announced as the Allergen of the Year by the American Contact Dermatitis Society in March 2023.¹ However, allergic contact dermatitis (ACD) to lanolin remains a matter of fierce debate among dermatologists. Herein, we discuss this important contact allergen, emphasizing the controversy behind its allergenicity and nuances to consider when patch testing.

What is Lanolin?

Lanolin is a greasy, yellow, fatlike substance derived from the sebaceous glands of sheep. It is extracted from wool using an intricate process of scouring with dilute alkali, centrifuging, and refining with hot alkali and bleach.² It is comprised of a complex mixture of esters, alcohols, sterols, fatty acids, lactose, and hydrocarbons.³

The hydrophobic property of lanolin helps sheep shed water from their coats.³ In humans, this hydrophobicity benefits the skin by retaining moisture already present in the epidermis. Lanolin can hold as much as twice its weight in water and may reduce transepidermal water loss by 20% to 30%.^4-6 In addition, lanolin maintains tissue breathability, which supports proper gas exchange, promoting wound healing and protecting against infection.^3,7

Many personal care products (PCPs), cosmetics, and topical medicaments contain lanolin, particularly products marketed to help restore dry cracked skin. The range of permitted concentrations of lanolin in over-the-counter products in the United States is 12.5% to 50%.³ Lanolin also may be found in industrial goods. The Table provides a comprehensive list of common items that may contain lanolin.^1,3,8,9

A Wolf in Sheep’s Clothing?

Despite its benefits, lanolin is a potential source of ACD. The first reported positive patch test (PPT) to lanolin worldwide was in the late 1920s.¹⁰ Subsequent cases of ACD to lanolin were described over the next 30 years, reaching a peak of recognition in the latter half of the 20th century with rates of PPT ranging from 0% to 7.4%, though the patient population and lanolin patch-test formulation used differed across studies.⁹ The North American Contact Dermatitis Group observed that 3.3% (1431/43,691) of patients tested from 2001 to 2018 had a PPT to either lanolin alcohol 30% in petrolatum (pet) or Amerchol L101 (10% lanolin alcohol dissolved in mineral oil) 50% pet.¹¹ Compared to patients referred for patch testing, the prevalence of contact allergy to lanolin is lower in the general population; 0.4% of the general population in Europe (N=3119) tested positive to wool alcohols 1.0 mg/cm² on the thin-layer rapid use Epicutaneous (TRUE) test.¹²

Allergic contact dermatitis to lanolin is unrelated to an allergy to wool itself, which probably does not exist, though wool is well known to cause irritant contact dermatitis, particularly in atopic individuals.¹³

Who Is at Risk for Lanolin Allergy?

In a recent comprehensive review of lanolin allergy, Jenkins and Belsito¹ summarized 4 high-risk subgroups of patients for the development of lanolin contact allergy: stasis dermatitis, chronic leg ulcers, atopic dermatitis (AD), and perianal/genital dermatitis. These chronic inflammatory skin conditions may increase the risk for ACD to lanolin via increased exposure in topical therapies and/or increased allergen penetration through an impaired epidermal barrier.^14-16 Demographically, older adults and children are at-risk groups, likely secondary to the higher prevalence of stasis dermatitis/leg ulcers in the former group and AD in the latter.¹

The allergenicity of lanolin is far from straightforward. In 1996, Wolf¹⁷ first described the “lanolin paradox,” modeled after the earlier “paraben paradox” described by Fisher.¹⁸ There are 4 clinical phenomena of the lanolin paradox¹⁷:

• Lanolin generally does not cause contact allergy when found in PCPs but may cause ACD when found in topical medicaments.
• Some patients can use lanolin-containing PCPs on healthy skin without issue but will develop ACD when a lanolin-containing topical medicament is applied to inflamed skin. This is because inflamed skin is more easily sensitized.
• False-negative patch test reactions to pure lanolin may occur. Since Wolf’s¹⁷ initial description of the paradox, free alcohols of lanolin have been found to be its principal allergen, though it also is possible that oxidation of lanolin could generate additional allergenic substances.¹
• Patch testing with wool alcohol 30% can generate both false-negative and false-positive results.

At one extreme, Kligman¹⁹ also was concerned about false-positive reactions to lanolin, describing lanolin allergy as a myth attributed to overzealous patch testing and a failure to appreciate the limitations of this diagnostic modality. Indeed, just having a PPT to lanolin (ie, contact allergy) does not automatically translate to a relevant ACD,¹ and determining the clinical relevance of a PPT is of utmost importance. In 2001, Wakelin et al²⁰ reported that the majority (71% [92/130]) of positive reactions to Amerchol L101 50% or 100% pet showed current clinical relevance. Data from the North American Contact Dermatitis Group in 2009 and in 2022 were similar, with 83.4% (529/634) of positive reactions to lanolin alcohol 30% pet and 86.5% (1238/1431) of positive reactions to Amerchol L101 50% pet classified as current clinical relevance.^11,21 These findings demonstrate that although lanolin may be a weak sensitizer, a PPT usually represents a highly relevant cause of dermatitis.

Considerations for Patch Testing

Considering Wolf’s¹⁷ claim that even pure lanolin is not an appropriate formulation to use for patch testing due to the risk for inaccurate results, you might now be wondering which preparation should be used. Mortensen²² popularized another compound, Amerchol L101, in 1979. In this small study of 60 patients with a PPT to lanolin and/or its derivatives, the highest proportion (37% [22/60]) were positive to Amerchol L101 but negative to wool alcohol 30%, suggesting the need to test to more than one preparation simultaneously.²² In a larger study by Miest et al,²³ 3.9% (11/268) of patients had a PPT to Amerchol L101 50% pet, whereas only 1.1% (3/268) had a PPT to lanolin alcohol 30% pet. This highlighted the importance of including Amerchol L101 when patch testing because it was thought to capture more positive results; however, some studies suggest that Amerchol L101 is not superior at predicting lanolin contact allergy vs lanolin alcohol 30% pet. The risk for an irritant reaction when patch testing with Amerchol L101 should be considered due to its mineral oil component.²⁴

Although there is no universal consensus to date, some investigators suggest patch testing both lanolin alcohol 30% pet and Amerchol L101 50% pet simultaneously.¹ The TRUE test utilizes 1000 µg/cm² of wool alcohols, while the North American 80 Comprehensive Series and the American Contact Dermatitis Society Core 90 Series contain Amerchol L101 50% pet. Patch testing to the most allergenic component of lanolin—the free fatty alcohols (particularly alkane-α,β-diols and alkane-α,ω-diols)—has been suggested,¹ though these formulations are not yet commercially available.

When available, the patient’s own lanolin-containing PCPs should be tested.¹ Performing a repeat open application test (ROAT) to a lanolin-containing product also may be highly useful to distinguish weak-positive from irritant patch test reactions and to determine if sensitized patients can tolerate lanolin-containing products on intact skin. To complete a ROAT, a patient should apply the suspected leave-on product to a patch of unaffected skin (classically the volar forearm) twice daily for at least 10 days.²⁵ If the application site is clear after 10 days, the patient is unlikely to have ACD to the product in question. Compared to patch testing, ROAT more accurately mimics a true use situation, which is particularly important for lanolin given its tendency to preferentially impact damaged or inflamed skin while sparing healthy skin.

Alternatives to Lanolin

Patients with confirmed ACD to lanolin may use plain petrolatum, a safe and inexpensive substitute with equivalent moisturizing efficacy. It can reduce transepidermal water loss by more than 98%,⁴ with essentially no risk for ACD. Humectants such as glycerin, sorbitol, and α-hydroxy acids also have moisturizing properties akin to those of lanolin. In addition, some oils may provide benefit to patients with chronic skin conditions. Sunflower seed oil and extra virgin coconut oil have anti-inflammatory, antibacterial, and barrier repair properties.^26,27 Allergic contact dermatitis to these oils rarely, if ever, occurs.²⁸

Final Interpretation

Lanolin is a well-known yet controversial contact allergen that is widely used in PCPs, cosmetics, topical medicaments, and industrial goods. Lanolin ACD preferentially impacts patients with stasis dermatitis, chronic leg ulcers, AD, and perianal/genital dermatitis. Patch testing with more than one lanolin formulation, including lanolin alcohol 30% pet and/or Amerchol L101 50% pet, as well as testing the patient’s own products may be necessary to confirm the diagnosis. In cases of ACD to lanolin, an alternative agent, such as plain petrolatum, may be used.

Skin reactions at insulin pump infusion sites are common among people with type 1 diabetes who use the devices and can lead to delivery failure, new research suggests.
 

Insulin pump use is increasingly common, but many patients experience infusion-site failure that in some cases leads to discontinuation. In a novel investigation, researchers at the University of Washington, Seattle, used biopsies and noninvasive imaging to compare insulin pump sites with control sites in 30 patients. Several differences were found at pump sites in comparison with control sites, including fibrosis, inflammation, eosinophils, and increased vessel density.

“These findings support allergic sensitization as a potentially common reaction at [insulin pump] sites. The leading candidates causing this include insulin preservatives, plastic materials, and adhesive glue used in device manufacturing,” wrote Andrea Kalus, MD, of the university’s dermatology division, and colleagues. The findings were published recently in Diabetes Care.

The inflammatory response, they wrote, “may result in tissue changes responsible for the infusion-site failures seen frequently in clinical practice.”

Such infusion site problems represent an “Achilles heel” of these otherwise highly beneficial devices, lead author Irl Hirsch, MD, professor of medicine in the division of metabolism, endocrinology, and nutrition, said in a statement. “It doesn’t really matter how good the technology is. We still don’t understand what is happening with the infusion sites, much less to [be able to] fix it.”
 

Significant differences between pump and nonpump sites

In the cross-sectional study, Dr. Kalus and colleagues used noninvasive optical coherence tomography (OCT) immediately prior to performing punch biopsies at three sites: the site currently in active use, the “recovery site” used 3-5 days prior to the procedures, and control sites never used for pump infusion. Punch biopsies were also performed at those sites.

The mean age of the patients was 48.3 years, the mean diabetes duration was 30.4 years, and the mean duration of pump use was 15.8 years. Nearly all patients (93.3%) reported itchiness at the site, and 76.7% reported skin redness.

Of the 25 patients for whom OCT imaging was successful, statistical analysis showed significant differences in vascular area density and the optical attenuation coefficient, a surrogate for skin inflammation, between the pump and control sites and between recovery sites and current pump sites. The greater vessel density is likely a result of injury and repair related to catheter insertion, the authors said.

In the biopsy samples, both current and recovery sites showed increased fibrosis, fibrin, inflammation, fat necrosis, vascularity, and eosinophils, compared with the control sites, but no significant differences were found between current and recovery sites.

Eosinophils: ‘The most surprising histologic finding’

Eosinophils were found in 73% of skin biopsy specimens from current sites and in 75% of specimens from recovery sites, compared with none from the control sites (for both, P < .01). In all study participants, eosinophils were found in at least one current and/or recovery infusion site deep in the dermis near the interface with fat. The number of eosinophils ranged from 0 to 31 per high-power field, with a median of 4.

The number of eosinophils didn’t vary by type of insulin or brand of pump, but higher counts were seen in those who had used pumps for less than 10 years, compared with more than 20 years (P = .02).

The prevalence and degree of eosinophils were “the most surprising histologic finding,” the authors wrote, adding that “eosinophils are not typically present as a component of resident inflammatory cells in the skin.”

While eosinophils may be present in normal wound healing, “the absolute number and density of eosinophil in these samples support a delayed-type hypersensitivity response, which is typically observed between 2 and 7 days after exposure to an allergen. ... Eosinophils are often correlated with symptoms of itchiness and likely explain the high percentage of participants who reported itchiness in this study,” Dr. Kalus and colleagues wrote.
 

Correlation found between inflammation and glycemic control

All participants used the Dexcom G6 continuous glucose monitor as part of their usual care. Inflammation scores were positively correlated with insulin dose (P = .009) and were negatively correlated with time in range (P = .01).

No other OCT or biopsy findings differed by duration of pump use, previous use of animal insulin, or type of insulin.

The reason for these findings is unclear, Dr. Hirsch said. “How much was the catheter or the insulin causing the irritation around the sites? How much was it from the preservatives, or is this because of the insulin pump itself? All these questions need to be answered in future studies. ... The real goal of all of this is to minimize skin damage and improve the experience for our patients.”

The study was funded by the Leona M. and Harry B. Helmsley Charitable Trust. Dr. Hirsch reported grants and contracts from Insulet, Medtronic, and Dexcom outside the submitted work; consulting fees from Abbott Diabetes Care, Lifescan, and Hagar outside the submitted work; and honoraria for lectures, presentations, participation on speaker’s bureaus, manuscript writing, or educational events as section editor for UpToDate outside the submitted work. Dr. Kalus has no disclosures.

A version of this article first appeared on Medscape.com.

Skin reactions at insulin pump infusion sites are common among people with type 1 diabetes who use the devices and can lead to delivery failure, new research suggests.
 

Insulin pump use is increasingly common, but many patients experience infusion-site failure that in some cases leads to discontinuation. In a novel investigation, researchers at the University of Washington, Seattle, used biopsies and noninvasive imaging to compare insulin pump sites with control sites in 30 patients. Several differences were found at pump sites in comparison with control sites, including fibrosis, inflammation, eosinophils, and increased vessel density.

“These findings support allergic sensitization as a potentially common reaction at [insulin pump] sites. The leading candidates causing this include insulin preservatives, plastic materials, and adhesive glue used in device manufacturing,” wrote Andrea Kalus, MD, of the university’s dermatology division, and colleagues. The findings were published recently in Diabetes Care.

The inflammatory response, they wrote, “may result in tissue changes responsible for the infusion-site failures seen frequently in clinical practice.”

Such infusion site problems represent an “Achilles heel” of these otherwise highly beneficial devices, lead author Irl Hirsch, MD, professor of medicine in the division of metabolism, endocrinology, and nutrition, said in a statement. “It doesn’t really matter how good the technology is. We still don’t understand what is happening with the infusion sites, much less to [be able to] fix it.”
 

Significant differences between pump and nonpump sites

In the cross-sectional study, Dr. Kalus and colleagues used noninvasive optical coherence tomography (OCT) immediately prior to performing punch biopsies at three sites: the site currently in active use, the “recovery site” used 3-5 days prior to the procedures, and control sites never used for pump infusion. Punch biopsies were also performed at those sites.

The mean age of the patients was 48.3 years, the mean diabetes duration was 30.4 years, and the mean duration of pump use was 15.8 years. Nearly all patients (93.3%) reported itchiness at the site, and 76.7% reported skin redness.

Of the 25 patients for whom OCT imaging was successful, statistical analysis showed significant differences in vascular area density and the optical attenuation coefficient, a surrogate for skin inflammation, between the pump and control sites and between recovery sites and current pump sites. The greater vessel density is likely a result of injury and repair related to catheter insertion, the authors said.

In the biopsy samples, both current and recovery sites showed increased fibrosis, fibrin, inflammation, fat necrosis, vascularity, and eosinophils, compared with the control sites, but no significant differences were found between current and recovery sites.

Eosinophils: ‘The most surprising histologic finding’

Eosinophils were found in 73% of skin biopsy specimens from current sites and in 75% of specimens from recovery sites, compared with none from the control sites (for both, P < .01). In all study participants, eosinophils were found in at least one current and/or recovery infusion site deep in the dermis near the interface with fat. The number of eosinophils ranged from 0 to 31 per high-power field, with a median of 4.

The number of eosinophils didn’t vary by type of insulin or brand of pump, but higher counts were seen in those who had used pumps for less than 10 years, compared with more than 20 years (P = .02).

The prevalence and degree of eosinophils were “the most surprising histologic finding,” the authors wrote, adding that “eosinophils are not typically present as a component of resident inflammatory cells in the skin.”

While eosinophils may be present in normal wound healing, “the absolute number and density of eosinophil in these samples support a delayed-type hypersensitivity response, which is typically observed between 2 and 7 days after exposure to an allergen. ... Eosinophils are often correlated with symptoms of itchiness and likely explain the high percentage of participants who reported itchiness in this study,” Dr. Kalus and colleagues wrote.
 

Correlation found between inflammation and glycemic control

All participants used the Dexcom G6 continuous glucose monitor as part of their usual care. Inflammation scores were positively correlated with insulin dose (P = .009) and were negatively correlated with time in range (P = .01).

No other OCT or biopsy findings differed by duration of pump use, previous use of animal insulin, or type of insulin.

The reason for these findings is unclear, Dr. Hirsch said. “How much was the catheter or the insulin causing the irritation around the sites? How much was it from the preservatives, or is this because of the insulin pump itself? All these questions need to be answered in future studies. ... The real goal of all of this is to minimize skin damage and improve the experience for our patients.”

The study was funded by the Leona M. and Harry B. Helmsley Charitable Trust. Dr. Hirsch reported grants and contracts from Insulet, Medtronic, and Dexcom outside the submitted work; consulting fees from Abbott Diabetes Care, Lifescan, and Hagar outside the submitted work; and honoraria for lectures, presentations, participation on speaker’s bureaus, manuscript writing, or educational events as section editor for UpToDate outside the submitted work. Dr. Kalus has no disclosures.

A version of this article first appeared on Medscape.com.

Skin reactions at insulin pump infusion sites are common among people with type 1 diabetes who use the devices and can lead to delivery failure, new research suggests.
 

Insulin pump use is increasingly common, but many patients experience infusion-site failure that in some cases leads to discontinuation. In a novel investigation, researchers at the University of Washington, Seattle, used biopsies and noninvasive imaging to compare insulin pump sites with control sites in 30 patients. Several differences were found at pump sites in comparison with control sites, including fibrosis, inflammation, eosinophils, and increased vessel density.

“These findings support allergic sensitization as a potentially common reaction at [insulin pump] sites. The leading candidates causing this include insulin preservatives, plastic materials, and adhesive glue used in device manufacturing,” wrote Andrea Kalus, MD, of the university’s dermatology division, and colleagues. The findings were published recently in Diabetes Care.

The inflammatory response, they wrote, “may result in tissue changes responsible for the infusion-site failures seen frequently in clinical practice.”

Such infusion site problems represent an “Achilles heel” of these otherwise highly beneficial devices, lead author Irl Hirsch, MD, professor of medicine in the division of metabolism, endocrinology, and nutrition, said in a statement. “It doesn’t really matter how good the technology is. We still don’t understand what is happening with the infusion sites, much less to [be able to] fix it.”
 

Significant differences between pump and nonpump sites

In the cross-sectional study, Dr. Kalus and colleagues used noninvasive optical coherence tomography (OCT) immediately prior to performing punch biopsies at three sites: the site currently in active use, the “recovery site” used 3-5 days prior to the procedures, and control sites never used for pump infusion. Punch biopsies were also performed at those sites.

The mean age of the patients was 48.3 years, the mean diabetes duration was 30.4 years, and the mean duration of pump use was 15.8 years. Nearly all patients (93.3%) reported itchiness at the site, and 76.7% reported skin redness.

Of the 25 patients for whom OCT imaging was successful, statistical analysis showed significant differences in vascular area density and the optical attenuation coefficient, a surrogate for skin inflammation, between the pump and control sites and between recovery sites and current pump sites. The greater vessel density is likely a result of injury and repair related to catheter insertion, the authors said.

In the biopsy samples, both current and recovery sites showed increased fibrosis, fibrin, inflammation, fat necrosis, vascularity, and eosinophils, compared with the control sites, but no significant differences were found between current and recovery sites.

Eosinophils: ‘The most surprising histologic finding’

Eosinophils were found in 73% of skin biopsy specimens from current sites and in 75% of specimens from recovery sites, compared with none from the control sites (for both, P < .01). In all study participants, eosinophils were found in at least one current and/or recovery infusion site deep in the dermis near the interface with fat. The number of eosinophils ranged from 0 to 31 per high-power field, with a median of 4.

The number of eosinophils didn’t vary by type of insulin or brand of pump, but higher counts were seen in those who had used pumps for less than 10 years, compared with more than 20 years (P = .02).

The prevalence and degree of eosinophils were “the most surprising histologic finding,” the authors wrote, adding that “eosinophils are not typically present as a component of resident inflammatory cells in the skin.”

While eosinophils may be present in normal wound healing, “the absolute number and density of eosinophil in these samples support a delayed-type hypersensitivity response, which is typically observed between 2 and 7 days after exposure to an allergen. ... Eosinophils are often correlated with symptoms of itchiness and likely explain the high percentage of participants who reported itchiness in this study,” Dr. Kalus and colleagues wrote.
 

Correlation found between inflammation and glycemic control

All participants used the Dexcom G6 continuous glucose monitor as part of their usual care. Inflammation scores were positively correlated with insulin dose (P = .009) and were negatively correlated with time in range (P = .01).

No other OCT or biopsy findings differed by duration of pump use, previous use of animal insulin, or type of insulin.

The reason for these findings is unclear, Dr. Hirsch said. “How much was the catheter or the insulin causing the irritation around the sites? How much was it from the preservatives, or is this because of the insulin pump itself? All these questions need to be answered in future studies. ... The real goal of all of this is to minimize skin damage and improve the experience for our patients.”

The study was funded by the Leona M. and Harry B. Helmsley Charitable Trust. Dr. Hirsch reported grants and contracts from Insulet, Medtronic, and Dexcom outside the submitted work; consulting fees from Abbott Diabetes Care, Lifescan, and Hagar outside the submitted work; and honoraria for lectures, presentations, participation on speaker’s bureaus, manuscript writing, or educational events as section editor for UpToDate outside the submitted work. Dr. Kalus has no disclosures.

A version of this article first appeared on Medscape.com.