Health Encyclopedia

Home | List of Topics | General Medical Information | Tests

Wood’s lamp

Definition

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

Alternative Names

Black light test; Ultraviolet light test

How the test is performed

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.

How to prepare for the test

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

You will feel nothing during this test.

Why the test is performed

Your health care provider may perform this test to detect several conditions, including:

• Bacterial infections
• Fungal infections
• Porphyria
• Pigmentary alterations

Normal Values

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

What abnormal results mean

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.

What the risks are

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

Special considerations

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.

Review Date:10/13/2006
Reviewed By:Kevin Berman, MD, PhD, Associate, Atlanta Center for Dermatologic Disease, Atlanta, GA. Review provided by VeriMed Healthcare Network.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is the first of its kind, requiring compliance with 53 standards of quality and accountability, verified by independent audit. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial process. A.D.A.M. is also a founding member of Hi-Ethics (www.hiethics.com) and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The Agency for Health Care Administration (Agency) and this website do not claim the information on, or referred to by, this site is error free. This site may include links to websites of other government agencies or private groups. Our Agency and this website do not control such sites and are not responsible for their content. Reference to or links to any other group, product, service, or information does not mean our Agency or this website approves of that group, product, service, or information.

Additionally, while health information provided through this website may be a valuable resource for the public, it is not designed to offer medical advice. Talk with your doctor about medical care questions you may have.