Skin Allergy Tests

Allergies and asthma often coexist. Allergies contribute to asthma in children, and many adults with asthma also have allergies. This is why skin tests are recommended to detect allergies in order to identify what triggers are to be avoided in order to limit asthmatic attacks.

There are three types of skin allergy tests:

Prick test, in which a drop of allergen is placed on the skin and an instrument, is used to pierce the skin at the site of the drop.

Scratch test, in which the surface of the skin is scraped with a needle and allergens are placed on the scratched surface.

Intradermal test, in which a small quantity of allergen is injected just below the upper layer of the skin.

Skin allergy tests are normally done on the arms and on the back. Of the three tests, prick test introduces least amount of allergen and is therefore done on the lower arm. Skin tests may not always give accurate results. This means that even if you have the allergy, the skin may not react or the skin may react even if you do not have the allergy.

A different skin test is recommended for each allergen. Thus, you may have to be tested for several allergens in order to detect all the substances you are allergic to. After the allergen is introduced into your skin, the doctor will be able to assess your reactions after about twenty minutes. The reaction causes red rashes with a pale centre, swelling and itching at the sites. The size of the reaction depends upon the severity of the allergy.

Some doctors prefer to use two control sites during the skin allergy tests. Normal saline is introduced to the first control site. This solution does not produce any reaction. Histamine, a known trigger of allergies is introduced to another site. You will have itching, burning, redness, swelling or blister formation at the site where histamine is introduced. These two control sites help the doctor to compare the severity of your reaction to the allergen.