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BCM - Baylor College of Medicine

Giving life to possible

Baylor Dermatology Clinic

Patch Testing - Frequently Asked Questions

What is patch testing?

Patch testing is a specialized procedure that tests for skin allergies. Allergies may occur to substances that come in contact with your skin. When this happens, a rash develops. An example is a rash that develops to nickel in jewelry. Skin allergy is different than breathing allergies. In an allergist's office, you may be tested with pin-prick testing. When we test for skin allergy, we apply patches to your back.

Can I undergo patch testing?

Before you can be tested, there are a few requirements. Your back, or most of it, must not have the rash. You cannot be taking prednisone by mouth or applying topical steroids to your back. You cannot have been treated with UVB or PUVA light treatments in the few days before the testing. We do not ever test pregnant women.

How is it done?

Patch testing appointments are always made as two-part appointments spaced 72 hours apart. On the first visit, we will discuss what substances you are exposed to. These include products that you use on your skin and substances that you may come into contact with at work or during hobbies. Please try to be as thorough as possible when discussing possible exposures. This helps us to determine what substances we will test.

Small amounts of these substances, which we call allergens, are then placed on small patches. These patches come in groups of 10 and are applied to your back. We reinforce these with tape because they need to stay in place for 48 hours.

What do I need to do?

While the patches are on your back, you need to take a few precautions. Your back may not get wet. You should limit sweating so that the patches do not come loose. After 48 hours, you will remove the tape and discard the patches. Even after the patches are removed, you should not let the back get wet or apply anything to the back. This allows us to get an accurate reading on your tests.

What should I do if my testing is positive?

At your second visit we examine the back for any reactions. If you did react to a substance, this is a positive test. We will discuss where this substance is found and how you may have been exposed to it. If you react to a substance, you should make every attempt to avoid it.

Will my rash go away?

Sometimes this substance is causing the rash. Other times, you may have an underlying skin condition, and this substance is worsening the skin condition. Occasionally, this substance may have no role in causing or worsening your rash. Only by avoiding the substance will you find out if it is playing a role.

If you do not react to any substances, we have excluded these substances as a cause of your rash, and you and your dermatologist may discuss further treatment options for your skin condition.