skin tests

Skin tests

People who have allergies may suffer from:

hives
rash or redness of skin
itchiness
swelling of the lips or eyelids
throat tightness
red, itching, watery eyes
frequent post-nasal drip
sneezing
itchy, scratchy, or sore throat
asthma or wheezing
coughing
fainting, sleepiness, or fatigue

To find out what is causing the allergy, your healthcare provider may refer you to an allergist. The allergist may perform allergy tests to find out the cause of the allergies.

Any substance that can cause an allergic reaction is called an allergen. These include: tree pollens; weeds; molds; cat or dog dander; dust mites; metals, like copper or nickel; foods, latex, venom from stinging insects such as bees; drugs, etc. Allergen extracts (vaccines) are available for each of these. The choice of which allergens are used depends on your allergic history.

Antihistamines can interfere with the skin tests. They should be stopped 1 to several days before the testing. There are 2 types of allergy skin tests.

The scratch or puncture test applies small drops of allergens to the top layer of skin on the back or lower arm. The skin under these drops is then lightly broken by pricking, puncturing, or scratching. An allergic reaction occurs when the area around that scratch becomes red and swollen within 15 minutes. These small hives go away within 30 minutes. The size of the hive will determine how allergic you are to that allergen. If you are not allergic to any allergens, the area where the drops were applied will remain normal. This test is usually the first test done because it:

is quick and easy
causes little or no discomfort
allows large numbers of allergens to be tested at one time and
rarely causes any serious reactions

The Intradermal test is similar, but is a little more accurate. It may be done when the reaction to a scratch test did not find the allergen. A tiny amount of the allergen is injected under the skin, usually on the upper arms or back. For this test:

the skin is cleaned well with a piece of gauze moistened with clear water, then wiped dry
a series of dots are made with a felt tip pen (1 dot for each allergen being tested)
a small drop of allergen extract is placed next to each dot
the drops are pressed onto the skin with the blunt end of a small needle

There is little or no pain with this test. Like the scratch test, if you are allergic, a red, raised area (a hive) will appear. The allergist will measure the hive to see how strong the reaction is.

If the tests are positive, you will know which allergens you are allergic to. This will help you avoid them and treat them. It also helps the allergist recommend treatments to manage your allergies, such as antihistamines, steroids, or a special vaccination with the allergen ("allergy shots").

Adults and children of all ages can be tested for allergies. If you think you may have hay fever allergies, or asthma affected by allergies, contact your healthcare provider and keep a record of all allergy symptoms (such as when they occur, activity at the time, the weather, foods eaten, and other related information).

Last Reviewed 2005

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.