A Wood's lamp examination is a test that uses ultraviolet light to closely look at the skin.

The test is done while you are seated in a dark room, usually in a dermatologist's office. The health care provider turns on the Wood's lamp, holds it 4 to 5 inches from the area of skin being studied, and looks for any skin color changes.

You should not look directly into the light.

No special preparation is needed. If you are treating the area in question with any topical medications, you may wish to skip an application before visiting the doctor.

You will feel nothing during this test.

Your health care provider may perform this test to detect several conditions affecting the skin, including

• Bacterial infections
• Fungal infections
• Porphyria
• Skin coloring changes

Normally your skin will not shine, or fluoresce, under the ultraviolet light.

A Wood's lamp exam may help your doctor confirm a fungal infection or bacterial infection. Your doctor may also be able to learn what is causing any light- or dark-colored spots on your skin.

There are no risks. Avoid looking directly into the ultraviolet light.

Do not wash before the test, because that may cause a false-negative result. A room that is not dark enough may also alter results. Other materials may also glow. For example, some deodorants, make-ups, soaps, and even lint may be visible with the Wood's lamp.

Not all types of bacteria and fungi can be detected with the light.