An allergy skin test, also called a scratch test, is used to identify the substances that are causing your allergy symptoms. It is performed by applying an extract of an allergen to your skin, scratching or pricking the skin to allow exposure, and then evaluating the skin's reaction.

What Happens During the Test?

First, a doctor or nurse will examine the skin on your forearm and clean it with alcohol. (Sometimes, the skin test is performed on an area of your back.)

Areas on your skin are then marked with a pen to identify each allergen that will be tested. A drop of extract for each potential allergen -- such as pollen, animal dander, or insect venom -- is placed on the corresponding mark. A small disposable pricking device is then used so the extract can enter into the outer layer of the skin, called the epidermis. The skin prick is not a shot and doesn't cause bleeding.

Sometimes, instead of the skin pricking method, a small amount of the allergen is injected just under the skin.

If there are allergic antibodies in your system, your skin will become irritated and may itch, much like a mosquito bite. This reaction means you are allergic to that substance.

How Long Does the Test Take?

Plan to spend about an hour for the entire appointment. The allergen placement part of the test takes about 5 to 10 minutes. Then you will have to wait about 15 minutes to see how your skin reacts.

How Should I Prepare for the Test?

Inform the healthcare provider who is going to perform the skin test about all medicines you are taking, including over-the-counter medications.

Since over-the-counter antihistamines stop allergic reactions, you should not take them for at least 48 hours before the test. Prescription antihistamines should be discontinued five to seven days before the test. Talk to your doctor about discontinuing your prescription medicines prior to the test.

Your doctor will give you a list of medicines to avoid before the test, since there are other drugs that can interfere with the results. Since you may not be able to discontinue certain medicines, the doctor or nurse may perform a separate "control" test to determine if that particular drug will interfere with the scratch test.

Does the Test Hurt?

The test may be mildly irritating, but most people say it doesn't hurt too much.

Is the Test Safe?

Although small amounts of allergens are introduced into your system, a skin test is safe when performed properly.

What Happens After the Test?

The extracts and ink marks will be cleaned off your skin with alcohol. A mild cortisone cream will be applied to your arm to relieve any itching at the sites of the skin pricks. Keep the tested area on your arm uncovered when you go home. Your doctor or allergist will use the results of the test to help develop a management plan for you.

When Should I Call My Doctor?

Call your doctor if you experience any of the following symptoms:

Fever
Lightheadedness
Wheezing
Shortness of breath

Reviewed by the doctors at The Cleveland Clinic Department of Pulmonary, Allergy and Critical Care Medicine.

Edited by Charlotte E. Grayson, MD, Feb. 2004, WebMD.

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