General, Surgical, and Cosmetic Dermatology
   for Adult and Pediatric Skin, Hair, and Nails

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   Patch Testing for Contact Allergens

For patients with chronic eczema or those who do not respond well to therapy, patch testing may be indicated. This diagnostic test provides information regarding possible sources of an allergic or irritant contact dermatitis.

For this diagnostic test, large pieces of medical tape with chemicals applied to small disks are placed on the back of unaffected skin. The patches remain on the person for 2 days (48 hours) and removed. Sensitivities to the chemical agents are identified at that time, and patients are asked to return in 1-3 days for a 2nd reading. Showers and baths are not permitted during the patch test, but patients are allowed to sponge bathe. At that time, literature is provided to the patient regarding his/her sensitivities, and the patient is instructed to avoid these chemicals. Patients follow up in 2 weeks to further discuss results and additional treatment options.

Patch testing is different from allergy testing. Allergy testing allows the physician to identify causes of allergies, including foods, dust, mites, grass, etc. Patch testing, on the other hand, helps identify causes of rashes. For example, hair dressers are often sensitive to paraphenylenediamine, a substance used in hair dyes; atopic dermatitis patients are typically sensitive to nickel.

Most dermatologists use the pre-packaged 24 panel Alloderm True Test patch test kits, primarily because of its convenience. However, we have found that we are only able to detect a subset of relevant allergens using the True Test. Thus, at Comprehensive Dermatology Centre, we perform a 50 panel patch test that is used and approved by the North American Contact Dermatitis Group. In addition to standard allergens, we test for steroid sensitivities, preservatives, rubber products, metals, and clothing dyes.

patch testing for allergens

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