Contact Dermatitis

Patch Testing 101, Part 2: After the Patch Test

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After the patch test, the physician must interpret positive reactions in the clinical context of the patient’s dermatitis. Relevance can be graded as current, past, or unknown. Counseling the patient on allergen avoidance is the most important step, and resources such as allergen information sheets and physician-generated safe lists from product databases can be used to help the patient both understand their allergens and avoid further exposure.

Practice Points

  • Positive patch test reactions must be interpreted in the context of the patient’s exposures, both current and past.
  • Allergen information sheets and product database safe lists are invaluable tools to help patients select safe skin care products.



The first part of this 2-part series addressed the basics of patch testing, including patch test systems, allergens, and patch test readings. In the second part of this series, we examine the incredibly important and absolutely vital steps that come after the patch test: determining relevance, patient counseling, and identifying allergen-free products for patient use. Let’s dive in!

Determining Relevance

The purpose of determining relevance is to assess whether the positive patch test explains the patient’s dermatitis. It is important to consider all of the patient’s exposures, including at home, at work, and during recreational activities. Several relevance grading scales exist. The North American Contact Dermatitis Group grades relevance as current, past, or unknown. Current relevance is further divided into definite, probable, and possible.1 Table 1 includes explanations and clinical examples of each relevance type.

True relevance is only known weeks or months after patch testing is complete. If the patient avoids allergens and is subsequently free of dermatitis, the allergens identified through patch testing were relevant. However, if the patient avoids allergens and sees no improvement in dermatitis, the allergens were not relevant. Gipson et al2 analyzed relevance as documented by the physician at final patch test reading vs patient opinion of relevance 30 days to 3 years after the final reading and found that there was variable agreement between the 2 groups; percentage agreement for formaldehyde-releasing preservatives was 88%, neomycin was 78%, nickel was 71%, fragrances was 65%, and gold was 56%. These differences underscore the need for ongoing research on patch test methods, determination of relevance, and standards for patient follow-up.2

Patient Counseling

Patient counseling is one of the most important and complex parts of patch testing. We have consulted with patients who had already completed patch testing with other providers but did not receive comprehensive allergen counseling and therefore did not improve. It is up to you to explain positive allergens to your patients in a way that they understand, can retain long-term, and can use to their advantage to keep their skin free of dermatitis, which is an incredibly difficult feat to accomplish. The resources that we describe next are the very basic requirements for proficient patch testing.

There are several tools that can be utilized to develop patch test counseling skills (Table 2). Membership with the American Contact Dermatitis Society (ACDS) includes opportunities for virtual and in-person (post–coronavirus disease 2019) lectures and conferences, videos, patch test support information, and patient resources. The European Society of Contact Dermatitis is similar, with a focus on European-based patch testers. Both societies are affiliated with academic journals—Dermatitis and Contact Dermatitis, respectively—which are phenomenal educational resources. Dermatitis Academy ( and Contact Dermatitis Institute ( are websites that are privately designed and managed by US-based patch test experts.


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