skin disorders
Diagnosis of Skin Disorders
Skin Tests
Skin tests, including a "use" test, a patch test, a prick (puncture) test, and an intradermal test, may be done if a doctor suspects an allergic reaction is the cause of a rash. Theuse test,in which a suspected substance is applied far from the original area where the rash occurred (usually on the forearm), is useful when perfumes, shampoos, or other substances found in the home may be the cause. In thepatch test,many small samples of common and suspected reaction-causing substances, known as allergens, are applied to the skin (typically on the upper back) under adhesive tape and left on. The skin under the patches is evaluated 48 hours later after the patches are removed and then again at 96 hours. It often takes the skin several days to produce a visible reaction. If a substance produces a characteristic, usually itchy rash, the person is probably allergic to it. In people who have light skin, the color of the rash is usually red. In people who have dark skin, the color of the rash may have less contrast with surrounding skin and thus be more subtle. Sometimes the substances produce an irritation that is not a true allergic reaction. a drop of an extract of the suspected substance is placed on the skin. Then, the drop is pricked or punctured with a needle to introduce a very tiny amount of the substance into the skin. The skin is then observed for redness (or other color changes), hives, or both, which usually occur within 30 minutes. (See also Skin testing .) tiny amounts of a substance are injected under the skin. The area is then watched for redness (or other color changes) and swelling, which indicate an allergic reaction. (See also Skin testing .) Although rare, prick and intradermal tests can cause a severe allergic reaction, known as Anaphylactic Reactions , which can be life threatening. Therefore, these types of tests should be done only by a trained health care professional. 