Patch Testing: Allergic contact dermatitis is tested by a procedure called patch testing

Allergic contact dermatitis is an uncomfortable and irritating rash that is caused by a substance (allergen) contacting the skin. It is often difficult to determine the specific cause, because chemicals, fragrances and preservatives in everyday products are frequently to blame, and there is often a delay between exposure and a rash developing.

Many people believe that if they have not been exposed to a new contact allergen, then an allergy is unlikely, but surprisingly, the reverse is true; the more frequently we are exposed to a product, the more likely we are to develop an allergy to one of its ingredients. Therefore, common household items are frequently the cause of allergic contact dermatitis.

Allergic contact dermatitis is tested by a procedure called patch testing. To perform patch testing, purified allergens are placed individually in chambers that are taped to a patient’s back and remain in place for about 48 hours. After 48 hours, the patches are removed and the underlying skin is examined (if a patient lives a significant distance from our clinic, this step can be done at home in many cases). The patient then returns about 24-48 hours later for one more reading. Positive contact allergens show up as small areas of inflamed skin on the patient’s back.

If one or more contact allergens are identified, then a person can begin the process of eliminating that allergen from their environment. We provide some tools to help with that, including information about the allergen and a “safe list” of products that do not contain the suspected allergens.