How is an allergy skin test usually done?

Patch or prick: Dermatologists using patch tests on back. Allergists using intradermal injections, usually through arms.

Prick testing: In an allergist's office, testing is started using a plastic prick (scratch) device. A small volume of the purified allergen is gently pricked on to the skin surface, usually the forearm or the back, with very little pain although it can be very itchy. If prick testing is negative, sometimes intradermal testing is done with small needles.

By an Allergist: After consulting with an allergist, he or she will perform skin prick testing by placing a purified allergen extract on the forearms or back and pricking/scratching it. If the patient is allergic to that exact allergen, redness, itchiness and a small hive will appear. Sometimes, intradermal testing is then performed by placing a slightly larger amount under the skin to help determine allergies.

Allergy skin testing: In the U.S., after antihistamine avoidance, 2 methods are often used--the prick/puncture (SPT) 1st, and sometimes the intradermal (IDT) 2nd. SPT involves allergen application to the forearm or back, along with a + and negative control, waiting 15-20 minutes and assessing for a bump and/or area of redness to determine if immune response occurs. IDT is similar but, placed below the epidermis.