International Academy of Cosmetic Dermatology

WOOD’S LIGHT

The Wood’s light, sometimes called a black light, was invented in 1903 by Robert W. Wood, a Baltimore physicist.  It was first used in dermatology by Margarot and Deveze to detect fungal infection in hair.

To achieve the emission of long-wave UV radiation (black light), a high pressure mercury arc is covered by a compound filter made of barium silicate with 9% nickel oxide.  This compound filter is referred to as a “Wood’s filter.” The Wood’s filter only permits the emission of radiation between 320 and 400 nm with a peak at 365 nm.  Initially, the skin absorbs the long-wave UV radiation (black light) and then emits radiation >400 nm which is visible.

The Wood’s light is useful in a variety of skin conditions:

1. Vitiligo.  Depigmented, as opposed to hypopigmented skin, glows white
2. Tinea versicolor. Malassezia furfur, a yeast causing tinea versicolor, emits a yellowish-white or copper-orange fluorescence.
3. Pseudomonas infection. This bacteria can create a green fluorescence.
4. Erythrasma.  Corynebacterium minutissimum, the bacteria that causes, erythrasma, an infection involving interdigital web spaces and intertriginous areas, gives acoral red fluorescence
5. Porphyria.   When shined on the urine of patients with certain types of porphyria, the Wood’s light creates reddish fluorescnence.

Noah Scheinfeld, MD, JD
New York, NY, USA

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