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: