Allergy Skin Tests: About These Tests

What are they?

Allergy skin tests are tests to find out if a substance, called an allergen, may cause an allergic response. A small amount of a suspected allergen is placed on or below the skin to see if a reaction develops.

Types of skin tests include:

• Skin prick test. For this test, a nurse lightly scratches or pricks your skin with a drop of a liquid that contains a possible allergen.
• Intradermal test. During this test, the nurse will inject a small amount of the allergen solution into your skin.

Why are these tests done?

Allergy skin tests are done to find out what things you are allergic to.

How do you prepare for the tests?

Be sure to tell your doctor about all the medicines you take. You may need to stop taking some medicines such as antihistamines for a few days before you have an allergy skin test.

How are these tests done?

For a skin prick test

The nurse will:

• Clean the test area (usually on your back or arm) with alcohol.
• Use a small device to scratch or prick your skin with drops of possible allergens. This allows some of the allergen to go into your skin.
• Check your skin after about 15 minutes for red, raised itchy areas called wheals. If a wheal forms, it means you are allergic to that allergen. This is called a positive reaction.

For an intradermal test

The nurse will:

• Clean the test area (usually on your back or arm) with alcohol.
• Inject the allergen solution into the skin.
• Check your skin after about 15 minutes for red, raised itchy areas called wheals. If a wheal forms, it means you are allergic to that allergen. This is called a positive reaction.

What happens after these tests?

The results of a skin prick or intradermal test will be available right after the test is done.

If you have an allergic reaction from any of the skin tests, you may have some itching, tenderness, and swelling where the allergen solutions were placed on your skin. After the testing is done, cool cloths or a nonprescription steroid cream can be used to relieve the itching and swelling.

How long do the tests take?

Allergy skin tests usually take less than an hour.