Ultraviolet Skin Imaging Using Wood’s Lamp: Principle, Indications, and Applications

Wood’s lamp is a specialized device used for non-invasive diagnosis of skin diseases, widely applied in cases of skin and hair conditions. This tool was invented in 1903 by physicist Robert Wood, and its first use in dermatology was documented in 1925, when it was recommended for detecting fungal infections.

Originally, the lamp was designed with a special filter that blocked visible light while transmitting only long-wave ultraviolet radiation (UV-A). Modern models employ LED light sources with a wavelength of 365 nm, providing significantly higher power density.

Wood’s Lamp Principle of Operation

When UV radiation interacts with certain skin conditions, it induces fluorescence — a physical process in which specific substances (endogenous or exogenous) absorb UV-A rays and emit light of a longer wavelength. This reaction is particularly pronounced in various microorganisms. Based on the color of fluorescence, a healthcare professional can make a preliminary assessment of the type, extent, and features of the lesion.

Indications and Fluorescence Colors

Wood’s lamp is used in dermatology to detect characteristic fluorescence associated with different pathologies.

Fungal infections

• Pityriasis versicolor: bright yellow-green fluorescence.
• Microsporia and dermatophytosis: bluish-green or bluish fluorescence.

Microsporia Lesion under White Lighting

Microsporia Lesion under Wood’s Lamp Illumination

Pityriasis Versicolor under White Lighting

Pityriasis Versicolor under Wood’s Lamp Illumination

Bacterial Infections

• Erythrasma: coral-red or red-orange fluorescence.
• Cutaneous pseudomoniasis: greenish fluorescence.
• Acne: red-orange fluorescence in sebaceous follicles.

Pigmentation Disorders

• Vitiligo: affected areas fluoresce with white-blue light and sharply defined borders.

Additional Diagnostic Applications

1. Porphyrias: characteristic pink-red fluorescence.
2. Hyper- and hypopigmentation (chloasma, melasma): Wood’s lamp helps determine the depth of pigment deposition.
3. Differential diagnosis: leukoderma, melanoderma, post-inflammatory pigmentation changes.
4. Skin hygiene assessment: detection of microbial imbalance and evaluation of skin cleanliness.

Diagnostic Technique

This is a non-invasive, rapid, and straightforward method.

• Setting: examination is performed in a darkened room or complete absence of light.
• Procedure: the healthcare professional switches on the lamp and examines the target areas from a distance of approximately 20 cm for several minutes.
• Evaluation: fluorescence is assessed for intensity, color, clarity of borders, and other parameters.
• Diagnosis: based on findings, a preliminary or final diagnosis is established; additional tests may be ordered if necessary.

Preparation for Examination

• 24 hours prior to the exam: do not cleanse the skin or apply creams, ointments, or any therapeutic/cosmetic products.
• 1–2 days prior to the exam: avoid baths, saunas, and tanning beds.

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Advantages and Limitations

Advantages

• Promptness: examination takes only a few minutes.
• Safety: the lamp does not emit harmful radiation.
• Comfort: the procedure is painless and causes no discomfort.
• Accessibility: the method is widely available in dermatological and other healthcare facilities.
• Visualization: the technique reveals pathological processes invisible under white light.

Limitations

• Restricted sensitivity: not all fungal and bacterial infections fluoresce under UV light.
• External factors: beauty products, ointments, and skin contaminants may distort results.
• Need for expertise: accurate interpretation requires extensive clinical experience.

Auxiliary role: the method is supplementary and does not replace laboratory diagnostics.