Wood’s lamp test is a diagnostic test used in dermatology that makes use of ultra violet rays for the close examination of the skin. The method of producing ultraviolet light was first devised by the scientist Robert Williams Wood. He used “Wood’s glass” to produce the ultraviolet light. But the use of ultraviolet rays in diagnosing skin problems started many years later. It was first experimented by two scientists Margarot and Deveze . They used ultraviolet light for the detection of fungal infection of hair.
Alternative names of Wood’s lamp test are Black light test and Ultraviolet light test.
The Woods lamp examination makes use of ultraviolet light with a wave length of approximately 365 nanometers. Here in this test the ultra violet light is shined over the part of the skin that is being examined. This test is usually carried out in a dark room. The physician or the health care provider will first the patient’s eyes to the darkness in the room, after that he will switch on the wood’s lamp to the site to be tested. The lamp will be held about 5-6 inches away from the patient’s body. The doctor then interprets the result depending on the change in the color of the skin.
The physician may ask to perform the Wood’s lamp test to detect several skin problems like infection by certain bacteria, fungal infections of the skin, hyper pigmentation and hypo pigmentation of skin, porphyria etc. It is also used to detect the ethylene glycol poisoning. Such poisoning mainly occurs as a result of antifreeze ingestion. During the manufacture of antifreezes that contains ethylene glycol, fluoresce is added. Thus, the poisoning by ethylene glycol can be detected as the urine of the patient fluoresces, when exposed to ultra violet light.
The Wood’s lamp test does not involve any risks. Even though the test does not have any side effects; the patient should avoid looking directly to the ultraviolet light.
The part of the skin to be tested should not be washed before the test as it may result in giving a false positive result. The patient should take but not apply any medication on this area as that might interfere with the test result. The room from which the test is being done should be dark as the absence of darkness may result in false positive result. Avoid contact with substances that may also show fluorescence like cosmetics, soaps, deodorants etc.
In normal case, the skin does not show any fluorescence or color change when exposed to ultraviolet light.
As the skin of a normal person does not fluoresce, any change in color indicates an abnormality. Each color indicates a specific bacterial or fungal infection or pigmentation problems.
For example: A golden yellow fluorescence shows Tinea versicolor infection, a bright yellowish green color indicates Trichophyton schoenleini infection, a Pink or Pinkish orange fluorescence shows infection by Porphyries Cutanea Tarda, a pale green color indicates Trichophyton Schoenleini infection, an aqua green or blue fluorescence indicates infection by the bacteria Pseudomonas aeruginosa, a bright yellowish green fluorescence shows infection by Microsporum canis, a bluish white color indicates leprosy, a pale white color indicates hypo pigmentation, a purplish brown fluorescence shows hyper pigmentation, a bright white color shows albinism, presence of ash leaf shaped patches shows tuberous sclerosis etc.