Wood's lamp is a test that is performed in a dark room, shining ultraviolet light on the area of interest.

You will be seated and the lights will be turned off. The health care provider will turn on the Wood's lamp and hold it four to five inches from the area being studied. The health care provider will look at your skin for any 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, including:

• Bacterial infections
• Fungal infections
• Porphyria
• Pigmentary alterations

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

Using the light, your doctor may be able to confirm a diagnosis of fungal infection or bacterial infection. Your doctor may also be able to learn what is causing the light- or dark-colored spots on your skin.

There are no risks, but avoid looking directly into the ultraviolet light, as you avoid looking into the sun.

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 infections can be detected with the light. Some species of fungi and bacteria do not contain fluorescent chemicals.