What's a Skin Test?

The most common way to test for allergies is on the skin, usually the forearm or the back. To do a typical skin prick test (also called a scratch test), an allergist or nurse will put a tiny bit of an allergen (such as a pollen or a food) on the skin, then make a small scratch or prick on the skin.

The allergist may put multiple allergens on the skin, testing for several food or environmental allergens in one visit. This can be a little uncomfortable and itchy. The allergist then waits 15 minutes or so to see if a red, raised bump, called a wheal, forms. If it does, there might be an allergy. The allergist uses a ruler to measure the wheal and the redness (called a flare) around it. The wheal and flare usually go away within 30 minutes to a few hours.

Skin prick tests are usually well tolerated. Rarely, they can cause a more serious allergic reaction. This is why skin testing must always be done in an allergist's office where the doctor is prepared to handle a reaction.

Other types of skin testing include injecting allergens into the skin (intradermal testing) or taping allergens to the skin for a period of time (patch testing).

What Allergens Can Skin Tests Check for?

With a skin prick test, an allergist can check for many kinds of allergies, such as:

• environmental, such as mold, dust mites, pet dander, or pollen
• food, such as peanuts or eggs
• medicines, such as penicillin

What Else Should I Know?

Some medicines (such as antihistamines) can affect skin testing. Check with the doctor to see if your child should stop taking any medicines before the test.

While skin testing is useful and helpful, sometimes doctors must do more tests (like blood tests or oral food challenges) to see if a child is truly allergic to something.