Here's what you should expect.

By Lauren Wellbank
June 12, 2020
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woman allergy batch testing
Credit: Getty / Science Photo Library

If you have a rash that you can't seem to shake, you may be tempted to call your dermatologist to set up an allergy screening. And for good reason: Knowing the root cause of your allergy symptoms is one of the first steps you need to take in order to treat them. However, before you show up for your appointment, you should know exactly what to expect, especially if your doctor would like to perform an allergy patch test. The test, which includes having small areas of your skin scratched and then covered with low doses of allergens to determine the cause of contact dermatitis, can be uncomfortable. Still, Dr. Debra Jaliman, a board-certified dermatologist in New York City, says the pros far outweigh the cons. Ahead, everything you need to know.

What to Expect

During the test, small patches are placed on your back; they contain substances that you could potentially be allergic to. Hypoallergenic tape is placed on top to secure the patches and act as a seal. The patches are generally left on the skin for a total of 72 hours, with a mid-way check performed at hour 48 to look for signs of irritation. "Initially, you are not allowed to bathe because you can't get the patches wet," Dr. Jaliman explains. "Then, 24 hours later, the patches are read again to make certain that you didn't have a delayed reaction." If the area becomes itchy and red—or you get a local hive—you'll know that you are having an immune response.

The Aftermath

Once you know identify these triggers, you can begin avoiding them—or become better prepared to treat a reaction when it occurs. For more intense reactions, you may need to carry an antihistamine for treatment on the go. And if your allergy is severe? Your doctor may prescribe an EpiPen so you can be proactive against anaphylactic shock.

How to Determine If You Really Need a Test

Not everyone will require patch testing, says Dr. Jaliman, since it is most often reserved for those who simply can't identify their allergens. "Let's say you can't use multiple shampoos, and even by the process of elimination, can't figure out which product you're allergic to," she explains. "This means that you need to figure out which ingredient in shampoo you're allergic to—which requires doing a patch test to determine the specific ingredient."

The Test Isn't for Everyone

If you are pregnant—or if you're already suffering from a severe allergic reaction—you wouldn't be a good candidate for patch testing. Taking steroids would also likely disqualify you; the medication is designed to suppress an immune response, rendering the test meaningless.

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