Skin Allergies and Patch Testing

Allergic contact dermatitis is a delayed-type cellular immune reaction that develops against certain substances the skin comes into contact with. Perfumes, preservatives, metals, hair dyes, acrylates, cosmetics, and some topical medications may be responsible.

Patch testing is the basic standard method for diagnosing contact allergy. In this test, standardized allergens are usually applied to the back and read at multiple times due to the delayed reaction.

Patch tests and prick tests are not the same. Patch tests investigate delayed-type contact allergy; prick tests, in appropriate clinical history, investigate immediate IgE-mediated allergy. Patch tests do not directly demonstrate irritant contact dermatitis and are not a routine test for chronic spontaneous urticaria.

The test is particularly valuable in recurrent facial/eyelid dermatitis, hand eczema, allergic contact cheilitis, hair dye reactions, cosmetic-related dermatitis, and occupational contact dermatitis. Additional allergen series can be added to the baseline series based on clinical history, and the patient's own products can be added under appropriate conditions.

A positive patch test only indicates sensitization. What's truly important is determining whether the positive allergen is clinically relevant to the patient's existing dermatitis. The test result should help identify the actual sources of exposure, rather than simply being a "list of banned substances.".

The 2026 ESCD guidelines define current standards for application materials, techniques, reading times, children, occupational dermatitis, drug rashes, patient-bred products, side effects, and outcome interpretation.