Skin tests

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

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What to expect: First, a doctor or nurse will examine the skin on your forearm and clean it with alcohol. (Sometimes, this test is performed on an area of the back.) Areas on your skin are then marked with a pen to identify each of the allergens that will be tested. A drop of an abstract made from each allergen--such as pollen, animal dander, or mold spore--is placed on the corresponding mark on your skin. A small disposable pricking device is then used to ensure that the extract enters 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.

The areas of the skin that become red and itchy indicate the substances that trigger a defensive response by your immune system. The skin reaction may be itchy, but most people say it doesn't hurt much.

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 (or back) to relieve any itching that may occur 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.

To prepare for the test: Antihistamines stop allergic reactions and should not be taken for at least 72 hours before the test.

Your doctor will give you a list of medications to avoid before the test, since there are other medications (such as tricyclic antidepressants) that will interfere with the test. Give the healthcare provider who is going to perform the skin test a list of all the medications you are taking, including over-the-counter ones. Talk to your doctor about discontinuing your prescription medications prior to the test.