Wood's Lamp Examination

Written by Tricia Kinman | Published on July 20, 2012
Medically Reviewed by George Krucik, MD

What Is Wood’s Lamp Examination?

The Wood’s lamp examination is a procedure that uses transillumination (light) to detect bacterial or fungal skin infections. It also can detect skin pigment disorders such as vitiligo or other irregularities in the skin. Sometimes the procedure is used to determine if you have a corneal abrasion (scratch) on the surface of your eye. The test can be called the black light test or the ultraviolet light test.

How Does It Work?

A Wood’s lamp is a small hand-held device that uses black light to illuminate areas that are otherwise difficult to see. The light is held over an area of skin in a darkened room. If present, bacteria or fungi will fluoresce (change color) under the light.

A fluorecin solution is poured on the eye when it’s used to test for scratches in or on the eye. Abrasions or scratches can be seen when the light shines on it. There are no risks associated with the procedure. However, you may want to shield your eyes from the ultraviolet light after the test.

What Do I Need to Know About This Test?

Avoid washing the area that will be tested before the procedure. Avoid using makeup, perfume, and deodorant on the area that will be tested, as these can alter the results of the examination.

The examination will take place in a doctor’s or dermatologist’s office. The procedure is simple and does not take a long time. The doctor will ask you to remove clothing from the area that will be examined. The doctor will then darken the room and hold the Wood’s lamp a few inches away from your skin to examine it under the light.

What Do the Results Mean?

Normally, the light will look purple or violet and your skin will not fluoresce (glow) or show any spots or under the Wood’s lamp. Your skin will change color if you have a fungal or bacterial, as fungi and some bacteria naturally luminesce under ultraviolet light.

A room that is not dark enough, perfumes, makeup, and skin products can discolor your skin and cause a “false positive” or “false negative” result. The Wood’s lamp does not test for all fungal and bacterial infections. Therefore, you may have an infection even if results are negative. Other tests may be needed to make a diagnosis.

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