Drugs on the skin surface- tetracyclines and mepacrine fluoresce after oral ingestion. Porphyrins used as the photosensitiser in photodynamic therapy. Porphyria causes red-pink fluorescence of the skin ( porphyria cutanea tarda), or teeth ( erythropoetic porphyria). Acne fluoresces orange-red due to cutibacteria in hair follicles. Pseudomonas in spa pool folliculitis and wound infection fluoresces green. Erythrasma-corynebacteria bacteria cause a pigmented rash in skin folds that fluoresces a coral-pink colour. Fungal infection due to other organisms does not fluoresce Microsporum species fluoresce blue-green ( M canis, M audouinii, M ferrugineum, M distortum) Trichophyton schoenleinii fluoresces dull blue. Tinea capitis-areas of scale and baldness due to fungal infection. Malassezia folliculitis-hair follicles fluoresce bluish-white. When active, the scale emits a yellowish or orange glow Pityriasis versicolor-a slightly scaly persistent rash on anterior chest and back caused by Malassezia yeasts. In contrast, areas of reduced blood flow are unchanged Hypopigmented skin has sharper borders under black light and fluoresces bright blue-white (or sometimes, yellowish green) due to accumulated biopterins. Loss of pigmentation (eg, vitiligo) or reduced pigmentation (eg, ash-leaf macules in tuberous sclerosis and hypomelanosis of Ito) to identify affected areas in light-skinned people. Pigmented lesions have a clear border under Wood light because the light is absorbed by increased melanin Increase in pigmentation (eg, melasma, postinflammatory pigmentation) to determine whether the pigmentation is epidermal (pigmentation enhanced by Wood lamp examination) or dermal (pigmentation unchanged by Wood lamp examination). What conditions are diagnosed using a Wood lamp?Ī Wood lamp for skin examination may reveal: Items on the skin surface such as fabric, topical medications and soap residue can also fluoresce. Clothing lint often shines bright white.Ī positive result is reported if a pigmentary disorder is more noticeable when examined using the Wood lamp or if fluorescence is noted.įluorescence is a coloured glow seen when certain substances such as collagen and porphyrins absorb black light and emit it again at a longer wavelength in the visible spectrum. Normal healthy skin is slightly blue but shows white spots where there is thickened skin, yellow where it is oily, and purple spots where it is dehydrated. The examination is painless and safe.Ī Wood lamp is used to identify the extent of pigmented or depigmented patches and to detect fluorescence. The lamp is held about 10-30 cm away from the skin. After waiting to adapt to the dark, the skin is examined with Wood lamp for a few seconds. Room lights are turned off, and window shades are drawn, or black drape used to darken the surroundings completely. The Wood lamp is turned on to warm up for about a minute. Gentle facial skin cleansing may be required 
Ideally, skin to be examined should not have been recently washed or had any makeup, deodorant or moisturising cream applied, as these can fluorescence causing a false positive result.A variety phosphors with different peak emissionĮxamination using Wood lamp involves the following steps.There are several models with varying properties.
Fluorescent black light tubes have a dark blue filter coating on the tube, which filters out most visible light. Modern black light sources may be specially designed BLB fluorescent lamps, mercury vapour lamps, light-emitting diodes, or incandescent lamps. The lamp was invented in 1903 by a Baltimore physicist, Robert W. What is a Wood lamp?Ī traditional Wood lamp is a low-output mercury arc covered by a Wood filter (barium silicate and 9% nickel oxide) and emits wavelength 320–450 nm (peak 365 nm). The lamp glows violet in a dark environment because it also emits some light in the violet part of the electromagnetic spectrum. Blacklight is invisible to the naked eye because it is in the ultraviolet spectrum, with a wavelength just shorter than the colour violet. Wood lamp examination is a diagnostic test in which the skin or hair is examined while exposed to the black light emitted by Wood lamp.
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