What is a Wood’s Lamp Evaluation?

A Wood’s lamp evaluation is a safe, painless dermatological test that uses long-wave ultraviolet (UV) light. It is used to identify fungal, bacterial or parasitic infections, pigmentary disorders or metabolic conditions. By examining how skin, scalp, or hair fluoresces or changes color, physicians can quickly screen for specific dermatologic issues.

A Wood’s lamp evaluation is also known as a blacklight test, ultraviolet light test or Wood’s light test. Blacklight is invisible to the naked eye because it is in the ultraviolet spectrum, with a wavelength just shorter than the color violet. The lamp was invented in 1903 by a Baltimore physicist, Robert W. Wood.

Clinical Significance

A Wood’s lamp examination is used in the diagnosis of many dermatologic disorders including:

  • Pigmentary disorders: Hypopigmentation or depigmentation, hyperpigmentation and melasma. 
  • Cutaneous infections: 
    • Fungal causes: Tinea versicolor, Pityrosporum folliculitis and Tinea capitis.
    • Bacterial causes: Corynebacterium minutissimum, Pseudomonas species and Propionibacterium acnes.
  • Porphyrias
Fluorescence in tinea capitis using Wood’s lamp.
Coral-pink fluorescence in erythrasma using Wood’s lamp.