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Alternative Names Return to topBlack light test; Ultraviolet light test
Definition Return to top
A Wood's lamp examination is a test that uses ultraviolet light to closely look at the skin.
How the Test is Performed Return to top
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.
How to Prepare for the Test Return to top
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.
How the Test Will Feel Return to top
You will feel nothing during this test.
Why the Test is Performed Return to top
Your health care provider may perform this test to detect several conditions affecting the skin, including
Normal Results Return to top
Normally your skin will not shine, or fluoresce, under the ultraviolet light.
What Abnormal Results Mean Return to top
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.
Risks Return to top
There are no risks. Avoid looking directly into the ultraviolet light.
Considerations Return to top
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.Update Date: 10/28/2008 Updated by: Michael Lehrer, M.D., Department of Dermatology, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.