Allergy Patch Testing


Allergy Patch Testing

Patch Testing is a common diagnostic tool used to identify the specific agent that triggers allergic skin rashes or “contact dermatitis”. Contact dermatitis is an itchy rash in response to a substance that you are allergic to, common trigger substances include poison ivy, jewelry, hair care products, cleaning solution, detergent, cosmetics, perfumes and latex rubber.

In allergic contact dermatitis, typically harmless substances cause an immune system reaction when they come in contact with the skin. Symptoms often include itching, redness, burning, rash, hives and /or blisters. The best protection against contact dermatitis is to identify and avoid the specific triggers with a Patch Test to help identify the trigger. It does not require the use of any needles or injections. Most dermatologists use the TRUE Test which is a very good screening tool but is limited to testing 28 chemicals. We offer expanded patch testing and regularly test to 60 allergens known to cause skin rashes in North America, called the North American Series of Allergens.

The Procedure

It is painless, and does not require use of needles or injections. Your doctor will tape several patches that contain various potential chemicals to the skin on the back. These chemicals are then left on the skin for 48 -72 hours and must remain dry during this time. Patients are advised to take only sponge baths and avoid excessive sweating.

After 48-72 hours, the patch test is removed and an initial reading is taken to observe any reactions.
An additional reading is taken after another 24 to 48 hours. Patients can bathe in between these readings, but should avoid scrubbing the back. Once the final results of the test have been read, normal bathing can be resumed. Before undergoing patch testing, patients should stop using oral and topical corticosteroids in the area. A positive test may show redness, bumps, mild swelling or even form a small blister. After completion of the test, topical steroids can be used to calm a symptomatic reaction on the back.Once positive results have been determined, patients can take steps to avoid their triggers and prevent contact dermatitis from occurring. Dr. Zelaya will provide you with specific information on your individual triggers and how to prevent contact.


It is important to avoid strenuous exercise that may loosen the patches or cause sweating during the patch testing week. Sun exposure to the testing area should be avoided for several weeks prior to your appointments. No showering is allowed during the patch testing. Sponge baths are permitted in areas not taped. (the lower body, underarms, etc.) Patch testing should not be performed if you are pregnant or breastfeeding.

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