A 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 and other skin irregularities. This procedure can also be used to determine if you have a corneal abrasion (scratch) on the surface of your eye. This test is also known as the black light test or the ultraviolet light test.
A Wood’s lamp is a small handheld device that uses black light to illuminate areas of your skin. The light is held over an area of skin in a darkened room. The presence of certain bacteria or fungi, or changes in the pigmentation of your skin will cause the affected area of your skin to change color under the light.
Some of the conditions that a Wood’s lamp examination can help diagnose include:
In the case of scratches on the eye, your doctor will put a fluorecin solution in your eye, then shine the Wood’s lamp over the affected area. Abrasions or scratches will glow when the light is on it. There are no risks associated with the procedure.
Avoid washing the area to be tested before the procedure. Avoid using makeup, perfume, and deodorant on the area that will be tested. The ingredients in some of these products can cause your skin to change color under the light.
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.
Normally, the light will look purple or violet and your skin will not fluoresce (glow) or show any spots under the Wood’s lamp. Your skin will change color if you have a fungal or bacterial, as some 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 still may have an infection, even if results are negative.
Your doctor may need to order more laboratory tests or physical exams before they are able to make a diagnosis.