The most common way to test for allergies is on the skin, usually the forearm or the back. In a typical skin test (also called a scratch test), a doctor or nurse will place a tiny bit of an allergen (such as pollen or food) on the skin, then prick the outer layer of skin or make a small scratch on the skin.
The allergist may repeat this, testing for several allergens in one visit. This can be a little uncomfortable, but not painful.
If a child reacts to one of the allergens, the skin will swell a little in that area. The doctor will be able to see if a reaction happens within about 15 minutes. The swelling usually goes down within about 30 minutes to a few hours. Other types of skin testing include injecting allergens into the skin or taping allergens to the skin for 48 hours.
With a skin test, an allergist can check for these kinds of allergies:
environmental, such as mold, pet dander, or tree pollen
Some medicines (such as antihistamines) can interfere with skin testing, so check with the doctor to see if your child's medications need to be stopped before the test is done. While skin testing is useful and helpful, sometimes more tests (like blood tests or food challenges) also must be done to see if a child is truly allergic to something.
While skin tests are usually well tolerated, in rare instances 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.