Skin tests are done in an allergist’s office.

There are two types of 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. A small amount of the possible allergen is injected under the skin through a thin needle.

An allergy occurs when you react to things like pollen or cats that don’t affect most people. If you come into contact with something you are allergic to (called an allergen), you may have symptoms such as itching or sneezing. This is called an allergic reaction.

A number of different allergens will be 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.

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. Talk to your allergist’s staff before the testing to find out which medications you can continue using.)

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.

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.

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. Whether given in shot form or under the tongue, immunotherapy involves giving gradually increasing doses of the substance to which you are allergic (also known as your allergen). The small increases over time in the amount of your allergen – things like dust, pollen, mold and pet dander – cause the immune system to become less sensitive to it. That reduces your allergy symptoms when you come across the allergen in the future. Immunotherapy also reduces the inflammation that comes with hay fever and asthma.

Allergists are experts who test for, diagnose and treat allergies.