A Wood lamp examination is a test that uses ultraviolet (UV) light to look at the skin closely.
Black light test; Ultraviolet light test
How the Test Is Performed
You sit in a dark room for this test. The test is usually done in a skin doctor's (dermatologist's) office. The doctor will turn on the Wood lamp and hold it 4 to 5 inches (10 to 12.5 centimeters) from the skin to look for color changes.
How to Prepare for the Test
You do not need to take any special steps before this test. Follow your doctor's instructions about not putting creams or medicines on the area of the skin before the test.
How the Test will Feel
You will have no discomfort during this test.
Why the Test Is Performed
This test is done to look for skin problems including:
- Bacterial infections
- Fungal infections
Porphyria(an inherited disorder that causes rashes, blistering, and scarring of the skin)
- Skin coloring changes, such as
vitiligoand some skin cancers
Not all types of bacteria and fungi show up under the light.
Normally the skin will not shine under the ultraviolet light.
What Abnormal Results Mean
A Wood lamp exam may help your doctor confirm a
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-up, soaps, and sometimes lint
DO NOT look directly into the ultraviolet light, as the light may harm the eye.
Habif TP. Light-related diseases and disorders of pigmentation. In: Habif TP, ed. Clinical Dermatology: A Color Guide to Diagnosis and Therapy. 6th ed. Philadelphia, PA: Elsevier; 2016:chap 19.
Spates ST. Diagnostic techniques. In: Fitzpatrick JE, Morelli JG, eds. Dermatology Secrets Plus. 5th ed. Philadelphia, PA: Elsevier; 2016:chap 3.
Review Date: 14/10/2018
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright ©2019 A.D.A.M., Inc., as modified by University of California San Francisco. Any duplication or distribution of the information contained herein is strictly prohibited.
Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Health. Please discuss with your doctor any questions or concerns you may have.