Practical Pearls

Patch Testing: Working With Patients to Find a Relevant Allergen

Author and Disclosure Information

The cause of ongoing dermatitis may be identified through patch testing. Finding a relevant allergen can help dermatologists offer treatments. Reviewing the process and expectations with patients is necessary to ensure optimal testing conditions. Treating allergic contact dermatitis once an allergen has been detected can be challenging. Herein, tips to guide dermatologists through the process with patients are provided.


What do your patients need to know at the first visit?

Patients with chronic dermatitis are frequently referred for patch testing. An in-depth conversation reviewing the patch test procedure and the many potential causes of dermatitis (eg, endogenous, allergic, irritant, seborrheic) is needed. Patients should understand the patch test process. The testing extends over a week, requiring 3 days of visits. The patches are applied at day 1 and must be kept dry and in place for 48 hours, then they are removed and evaluated. A second follow-up visit at 96 hours to 1 week after the patches are applied is done to perform a final read, interpret, and explain the final results. The patient needs to know that we are looking for an allergen that might be causing the eruption through contact exposure with the skin. The difference between patch testing and prick testing often needs to be discussed, as patients are not always aware of the difference. Explaining the need to avoid topical steroids at the patch test site, sunburn, or systemic steroids during the patch test period is also important to obtain optimal testing conditions.

Querying all exposures including work, home, personal care products, and hobbies is important to help determine which allergen series should be tested to obtain the best results. Patients need to understand that even small intermittent exposures can cause an ongoing dermatitis. If a causative allergen(s) is identified, strict avoidance can lead to clearance and resolution.

Setting expectations is important, and therefore you should discuss the possibility that no allergen will be identified while letting the patient know that this information is also useful. Also, let patients know there are other things that can be done if patch testing is negative to try and gain control of the dermatitis including laboratory tests and biopsies, which may be needed to help direct future management.

What are your go-to treatments? What are the side effects?

The beauty of patch testing is that finding a relevant allergen and subsequent avoidance of that allergen often is sufficient to improve or clear the dermatitis. Detailed education regarding the allergen, where it is found, and how to avoid it are imperative in patient management. I provide the patient with information sheets or narratives found on the American Contact Dermatitis Society website ( as well as a list of safe products found on the Contact Allergen Management Program (CAMP) area of the site. These tools help in patient compliance.

Go-to treatments for relevant patch test dermatitis involve topical steroids to calm the acute dermatitis while educating and instituting a personal environment free of the identified allergens. Occasionally, systemic steroids are used to provide relief and calm down an extensive dermatitis while educating, identifying, and eliminating known allergens from the patient’s environment. Identifying and eliminating an allergen can mitigate the need for chronic steroids, and the resultant side effects of hypertension, osteoporosis, avascular necrosis, hyperglycemia, and gastrointestinal tract problems can be avoided. Likewise, avoidance of allergens can lead to the elimination of the need for chronic topical steroids and the resultant atrophy and striae.

Side effects of the patch test procedure itself include an allergic reaction to one of the chemicals tested (eg, gold), which is what you are looking for; persistent reactions; flaring of existing dermatitis; irritation; hyperpigmentation; and rarely anaphylaxis or infection at a patch test site. If no allergy is found, treatment of generalized dermatitis can include topical steroids. Topical calcineurin inhibitors can be useful as well as narrowband UV light. Several oral medications can be used for recalcitrant patch test–negative dermatitis and the selection of the right medication is based on the patient’s comorbidities and extent of dermatitis, including systemic steroids, though long-term use is not recommended. Mycophenolate mofetil, methotrexate, cyclosporine, and azathioprine all have side effects including liver and renal toxicity, immunosuppression, and risk for malignancy and therefore need to be considered on a case-by-case basis.

How do you keep the patient compliant with treatment?

Treating allergic contact dermatitis once an allergen(s) has been identified can be challenging. Education is key so that the patient understands where the allergen is found in his/her environment and how to avoid it. Teaching the patient to read labels also is important. Providing a list of safe products simplifies compliance. Reinforcing the need for ongoing vigilance in allergen avoidance is critical to resolution of the dermatitis. Reinforcing the need for continuous avoidance is imperative, as patients sometimes become less vigilant once the dermatitis resolves and the allergen can sneak back into their environment.


Next Article:

Atopic Dermatitis Treatments Moving Forward: Report From the AAD Meeting

Related Articles