Wood's Lamp
The Wood's lamp is a classic non-invasive diagnostic tool in dermatology. It uses a long-wave ultraviolet A (UVA) light source with a special filter (Wood's glass, containing barium silicate and nickel oxide) to emit a beam that peaks at around 365 nm.
Invented by the physicist Robert Williams Wood in 1903 and brought into dermatology in 1925, the Wood's lamp relies on fluorescence and optical absorption. When UVA light hits the skin, microbial metabolites, melanin at different depths and certain skin structures absorb the energy and give it back off as visible light in characteristic wavelengths and colors.
At Haute-Derma, the Wood's lamp is an essential first-line diagnostic tool. It helps our doctors pinpoint the depth of pigmentary lesions such as melasma and quickly detect fungal and bacterial infections or depigmenting disorders that are hard to see with the naked eye.
How It Works: Biological Fluorescence
The diagnostic value of the Wood's lamp rests on a few key optical and skin-biology principles:
- Biological fluorescence: Specific organic molecules (fluorophores) in microorganisms or tissue absorb energy from UVA light (365 nm), shift energy state and then emit light at a longer wavelength within the visible range, producing distinctive fluorescent colors.
- Melanin contrast varies with depth: Melanin at different levels of the skin reacts differently to UVA light. Epidermal melanin absorbs strongly under the Wood's lamp and increases contrast, so the lesion looks darker and sharper. Dermal melanin, by contrast, lies beneath overlying layers of tissue and shows no clear change in contrast under the lamp.
- Blocking ambient visible light: The lamp's special filter lets UVA through while blocking most ordinary visible light, creating ideal optical conditions for spotting faint fluorescent signals.
Fluorescence Colors and Their Clinical Meaning
| Fluorescence Color Under Wood's Lamp | Corresponding Organism / Condition | Biological Cause of the Color |
|---|---|---|
| Bright green | Scalp ringworm caused by Microsporum canis or Microsporum audouinii. | Pteridine metabolites produced by the fungus on the hair shaft. |
| Coral red / orange-red | Intertrigo caused by Corynebacterium minutissimum (erythrasma). | The bacteria produce and accumulate coproporphyrin III. |
| Yellow-green / blue-green | Infection with Pseudomonas aeruginosa. | The bacteria secrete pyoverdine (fluorescein), which fluoresces under UVA. |
| Pigment appears darker than surrounding skin (enhanced contrast) | Epidermal melasma or superficial post-inflammatory hyperpigmentation. | Melanin is densely concentrated in the epidermis, absorbing strongly and creating high contrast. |
| No change in contrast / faint | Dermal melasma, or nevus of Ota / Hori's nevus. | Melanin lies deep in the dermis below the basement membrane, so it creates little contrast under UVA. |
| Even bright white / pale blue | Normal healthy skin, or sun-induced keratosis. | Natural light reflection from the stratum corneum and collagen structure. |
Our Wood's Lamp Examination Protocol at Haute-Derma
To make Wood's lamp findings as accurate as possible, we perform the examination at Haute-Derma under tightly controlled conditions:
- A fully darkened room: The patient is taken to a dedicated dark room with all outside light sources eliminated, so the eyes can adapt and the faintest fluorescent signals can be seen.
- Skin preparation: The area to be examined is cleaned, and no cosmetics, moisturizer, soap or alcohol antiseptic should remain on the skin beforehand, because many chemical ingredients, preservatives and mineral oils can also fluoresce and lead to a misleading result.
- Illumination and assessment: The Wood's lamp is switched on and allowed to reach a stable output, then held 10–15 cm from the skin and aimed perpendicular to it. The doctor directly assesses the colors and borders of the lesions and records clinical photographs.
Treatment Planning and Multimodal Care at Haute-Derma
What we see under the Wood's lamp guides the choice of treatment at Haute-Derma:
- Personalized plans for pigment disorders (melasma and hyperpigmentation): If the pigment stands out clearly under the lamp (epidermal melasma), we focus on pigment-suppressing actives (tranexamic acid, carefully supervised hydroquinone) combined with brightening mesotherapy. If the pigment looks faint under the lamp (dermal melasma), we shift to long-wavelength Nd:YAG or picosecond laser to break up deeper melanin.
- Accurate treatment of infections: When we see the characteristic fluorescence of a fungus (green) or bacteria (coral red), the doctor starts targeted topical or oral antifungal or antibiotic treatment right away, which also prevents patients from mistakenly using corticosteroid creams that would make the condition worse.
