Allergy Skin Testing Process

Allergy skin testing is done to find out exactly what things a person may be allergic to. Skin tests are done in an allergist’s office.

There are two types of allergy skin tests:

  • Prick or scratch test. In this test, a tiny drop of a possible allergen—something you are allergic to— is pricked or scratched into the skin. (This is also called a percutaneous test.) It is the most common type of skin test.
  • Intradermal test. This test shows whether someone is allergic to things such as insect stings and penicillin. A small amount of the possible allergen is injected under the skin through a thin needle.

What can I expect during allergy skin testing?

Anywhere from 10 to 50 different allergens are tested. It takes about 5 to 10 minutes to place the allergens on your skin. They are usually put on the forearm in adults and on the back in children. Then you will wait about 15 minutes to see if a small red lump appears where any of the allergens were placed.

The prick or scratch test and intradermal test may hurt slightly. If you are sensitive to any of the allergens, your skin may itch where the allergen was placed.

How should I prepare for the test?

  • Tell your allergist about all medicines you’re taking, including over-the-counter medicines.
  • Don’t take antihistamines for 3 to 7 days before the test. Ask your allergist when to stop taking them. (It’s okay to use nose (nasal) steroid sprays and asthma medicines. They will not interfere with skin tests.)

Is the test safe?

Very small amounts of allergens are tested on your skin, so skin testing is safe. During the test, the allergist will watch for a possible severe allergic reaction, but it rarely happens.

What do the skin test results mean?

If you’re sensitive to an allergen:

  • With the prick or scratch test and intradermal test, a small red bump appears on the skin where that allergen was placed, and this area may itch. The larger the bump, the more sensitive you may be to it.

These results are called positive skin tests and mean that you may be allergic to the allergen tested.

Even if a skin test shows that you’re allergic to something, you may not react to it when you’re exposed to it later. Your allergist will review your medical history and skin test results to help find out what you’re allergic to.

What happens if the skin test shows I have allergies?

Your allergist will create a plan for controlling your allergies. This means preventing and treating symptoms. Take these steps:

  • Avoid or limit contact with your allergens. For example, if you’re allergic to dust mites, reduce the clutter in your house, which collects dust.
  • Take medicine to relieve your symptoms. Your allergist may prescribe medicines such as antihistamines, decongestants, nose (nasal) sprays, or eye drops.
  • Get allergy shots if the allergist says you should. Some people need them when they can’t avoid an allergen. The shots contain a tiny but increasing amount of the allergen you’re sensitive to. Over time, your body becomes used to the allergen and no longer reacts to it.

Skin test should be performed by allergists, as they are experts who know how to test for, diagnose and treat allergies.