Patch testing is performed in order to find out what substance(s) are creating an allergic reaction on the skin.
The “patches” are a standard set of allergens that are applied to the skin. The set includes the most common substances that trigger allergic contact dermatitis, also known as simply skin allergies.
If the patient’s own products (for example: lotion or makeup) are suspected to be causing an allergic reaction, patch testing will be customized. Another set of “patches” that contain the patient’s personal skin products will be added to the set of patches.
Patch testing will take a bit of time to perform. The process is time consuming, but the results will help your doctor narrow down what is causing your symptoms and bring you closer to treatment! Sweating and heat can cause the tests to be invalid; so it is best to avoid showering, exercise, and extreme heat or humidity during the testing period. Sun exposure should be avoided before testing and for at least four weeks after testing. Three visits are required in one week:
During the first visit, the patches are applied, usually on the skin of the back. The patches are small strips of tape containing diluted substances (the possible allergens).
After two days, the patches are removed and the doctor makes an initial reading. The two days are needed so that the allergens have enough time to diffuse into the skin. It is best to wait to read the results until the redness from having the patch removed has gone away.
The third and final visit is when the doctor will read the results again. This is necessary in order to determine whether a reaction is an irritant reaction or a true allergic reaction.