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

Black light test; Ultraviolet light test

You will sit in a dark room for this test. The test usually takes place in a dermatologist's office. The health care provider will turn on the Wood's lamp and hold it 4 - 5 inches from the skin to look for color changes. 

You do not need to take any special steps before this test. Ask your doctor if you avoid putting creams or medicines on the area of the skin being studies before the test. 

You will feel nothing during this test.

Your health care provider may do this to look for skin problems including: 

• Bacterial infections
• Fungal infections
• Porphyria
• Skin coloring changes such as vitiligo

Normally your skin will not shine 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.

The following things can change the results of the test:

• Washing your skin before the test (may cause a false-negative result)
• A room that is not dark enough
• Other materials that glow under the light, such as some deodorants, make-ups, soaps, and sometimes lint

Not all types of bacteria and fungi show up under the light.

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