Diagnosis
Doctors can identify many skin disorders simply by looking at the skin. Revealing characteristics include size, shape, color, and location of the abnormality as well as the presence or absence of other signs or symptoms. To check the distribution of a skin problem, the doctor usually asks the person to undress completely, even though the person may have noticed an abnormality on only a small area of skin.
Sometimes, a biopsy must be performed, in which a small piece of skin is removed for examination under a microscope. For this simple procedure, the doctor generally numbs a small area of skin with a local anesthetic and, using a small knife (scalpel), scissors, or round cutter (punch biopsy), removes a piece of skin about 1/8 inch in diameter.
When an infection is suspected, a doctor may scrape off some material from the skin and examine it under a microscope. The material can also be sent to a laboratory, where the specimen is placed in a culture medium (a substance that allows microorganisms to grow). If the specimen contains any bacteria, fungi, or viruses, they grow in the culture and can be identified.
In a Wood's light examination, also used when certain skin infections are suspected, the skin is illuminated with an ultraviolet light in a dark room. The ultraviolet light makes some fungi or bacteria glow brightly and may make some pigmentation abnormalities, such as vitiligo, more visible.
Skin tests, including a patch test, a prick test, and an intradermal test, may be performed if a doctor suspects an allergic reaction as the cause of a rash. In the patch test, small samples of possible causative agents are held against the skin for 1 to 2 days. If the substance produces a rash, the person is allergic to it. In the prick test and intradermal test (see Section 16, Chapter 185), tiny amounts of a substance are injected under the skin. The area is then watched for redness and swelling, which indicate an allergic reaction.
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