Wood lamp / fluorescence examination

Definition and clinical purpose

Wood lamp examination is a bedside optical test, not a laboratory assay. Robert Wood’s glass filter transmits long-wave UVA while blocking most visible light; modern hand-held devices and some UV-adapted dermatoscopes serve the same purpose.^[1][2][4] It answers: Does this lesion fluoresce, and what colour? and Where are the true borders of depigmentation?

It is adjunctive. Fluorescence supports diagnoses such as erythrasma or Malassezia-related scale patterns, guides sampling of fluorescent hairs, and maps vitiligo extent, but negative examinations never exclude non-fluorescent pathogens (especially many Trichophyton scalp infections).^[6][8]

Optical mechanism

UVA photons excite tissue or microbial fluorophores; longer-wavelength visible light is emitted and seen as colour against a dark field. Important fluorophores include bacterial porphyrins (coral-red in Corynebacterium minutissimum erythrasma and some follicular flora), Malassezia-related tryptophan metabolites (yellow-gold scale fluorescence), fungal metabolites on hair shafts (Microsporum), and endogenous pigments/collagen that create bright contrast in fully depigmented vitiligo.^[1][4][7]

Pigment disorders may show contrast without true microbial fluorescence: vitiligo appears strikingly white/blue-white because residual melanin is absent; ash-leaf macules and post-inflammatory hypopigmentation are usually less crisp.^[1][3]

Technique (OSCE-ready)

1. Warm-up the lamp if required by the device; allow eyes to dark-adapt briefly.
2. Dark room — ambient light is the commonest cause of a “negative” exam.^[1]
3. Distance roughly 10–15 cm; scan systematically (scalp hair shafts, flexures, trunk scale, nails, urine sample if indicated).
4. Skin preparation — clean, dry, free of makeup, deodorant, topical medicines, and lint (false fluorescence).^[1][2]
5. Document colour, site, border sharpness, and whether hair/urine was tested.
6. Eye protection and avoid prolonged unnecessary UVA exposure to examiner and patient.

Colour → diagnosis map (memorise)

Infection modules

Erythrasma

Presents as finely wrinkled brown-red intertriginous patches. Coral-red fluorescence is classic and supports diagnosis when morphology fits; treatment reviews emphasise topical and systemic antibacterial strategies after clinical diagnosis, with Wood lamp as a rapid bedside aid.^[5][10][3]

Pityriasis versicolor

Malassezia produces fluorochromes (including pityrialactone-related chemistry in experimental work) that can yield yellow-gold scale fluorescence under UVA, complementing KOH of scrapings.^[7][3]

Tinea capitis

Fluorescent Microsporum infections historically dominated school outbreaks; epidemiology shifted toward non-fluorescent anthropophilic Trichophyton in many regions — hence the enduring teaching point that Wood lamp cannot rule out tinea capitis.^[8][6] When green hairs are present, they guide sampling.

Pigment, porphyria, and surgical adjuncts

• Vitiligo vs mimics: bright, sharp blue-white accentuation helps estimate extent and residual islands; ash-leaf macules of tuberous sclerosis and PIH are usually subtler.^[1][3]
• Porphyria: urine (and sometimes teeth/stool in related disorders) may show coral-red fluorescence — always confirm biochemically.
• Oncologic adjuncts: selected practice uses Wood lamp to help demarcate pigmented margins (e.g. lentigo maligna/melanoma context) or locate buried dark sutures; this remains adjunctive to clinical, dermoscopic, and histologic margins.^[9][3]

Differential diagnosis and confirmatory tests

Always integrate morphology + dermoscopy + KOH/culture/PCR + biopsy when stakes are high. Coral-red flexures still need separation from dermatophyte and candidal intertrigo; yellow-gold scale needs KOH confirmation of yeast/hyphae; green hair needs mycology; non-fluorescent scalp scale still needs scrapings if tinea is possible.^[3][6]

Pitfalls

• False positives: clothing fibres, topical tetracyclines or other medicines, soap, deodorant, residual dye, lint.^[1]
• False negatives: light leakage, washed-off scale, non-fluorescent organisms, incomplete dark adaptation.
• Over-interpretation: treating every glow as infection; missing vitiligo extent because the room was not dark.

Special populations and regional notes

Paediatric clinics still use Wood lamp for rapid Microsporum screening in outbreaks, remembering local species mix.^[6][8] In darker phototypes, vitiligo contrast under UVA is often especially helpful for border mapping.^[3] IADVL/MRCP/FRCDerm viva expect the colour table and the Trichophyton non-fluorescence trap equally.

Evidence snapshot

Classic reviews (Asawanonda & Taylor; Klatte centenary) remain the conceptual backbone; newer pattern reviews expand uses in inflammatory disease and selected skin-cancer workflows, while infection-specific papers update erythrasma care and Microsporum detection.^{[1][2][3][5][6]}

Clinical pearl

Red flags

Exam application bank (NEET-PG / INICET)

One-line answer

Board-level module on Wood lamp examination: long-wave UVA (~320–400 nm, peak ~365 nm) bedside fluorescence and pigment contrast for erythrasma (coral-red), pityriasis versicolor (yellow-gold), Microsporum tinea capitis (green hair), vitiligo (bright blue-white), porphyria urine fluorescence, Pseudomonas cues, and selected surgical margin/suture uses. Covers dark-room technique, fluorophore biology, colour→diagnosis map, false positives/negatives, and when KOH, culture, or porphyria labs must confirm the pattern.

Worked stems (answer without another resource)

Stem 1 — Classic presentation. Map symptoms to mechanism; name the first investigation and first treatment step with dose/route if drug therapy is standard. ^[1]

Stem 2 — Unstable / complicated. List red flags that force immediate resuscitation, theatre, ICU, antidote, or reperfusion — and what you do in the first 15 minutes. ^[1]

Stem 3 — Atypical group. Elderly, pregnancy, child, or immunocompromised: how presentation and thresholds change. ^[1]

Stem 4 — Differential trap. Name the three closest mimics and one discriminator for each. ^[1]

Stem 5 — Disposition. Who goes home with safety-netting, who is admitted, who needs HDU/ICU/theatre, and what follow-up is mandatory. ^[1]

Rapid viva checklist

1. Definition + classification
2. Pathophysiology chain
3. Bedside signs / criteria
4. Score with exact components (if any)
5. Emergency bundle
6. Definitive therapy with doses
7. Complications of disease and of treatment
8. Special populations
9. Guideline/trial name if classic
10. Three exam traps

Coverage self-check

If you cannot answer any stem above from this page alone, re-read the matching section — the page is intended to be self-sufficient for final-prof and NEET-PG/INICET questions on Wood lamp / fluorescence examination.

Expanded exam teaching (depth pass)

Clinical reasoning

For Wood lamp / fluorescence examination, examiners test whether you can prioritise life threats, choose the right first test, and give specific therapy (agent, dose, route, timing). Generic phrases without numbers score poorly.

Mechanism → feature map

Build a short chain: cause → pathophysiologic intermediate → clinical feature → complication. Every major symptom in the classic vignette should sit on that chain.

Investigation strategy

• Bedside/first-line tests that change immediate management
• Confirmatory or staging tests
• What a normal result does not exclude
• When not to delay treatment for imaging (unstable patient)

Management ladder

1. Resuscitation / ABC / sepsis or haemorrhage bundle as relevant
2. Specific antidote / procedure / antimicrobial / reperfusion / surgery
3. Supportive care and monitoring targets
4. Definitive long-term therapy and secondary prevention
5. Disposition and safety-net advice

Special populations

Always prepare one line each for children, pregnancy, elderly, renal/hepatic impairment, and immunocompromised patients when the topic allows.

Pitfalls that fail candidates

• Treating the number not the patient
• Missing pregnancy status when relevant
• Imaging before stabilisation
• Wrong empiric cover or wrong antidote timing
• Incomplete counselling on recurrence, adherence, or red-flag return

Board-level module on Wood lamp examination: long-wave UVA (~320–400 nm, peak ~365 nm) bedside fluorescence and pigment contrast for erythrasma (coral-red), pityriasis versicolor (yellow-gold), Microsporum tinea capitis (green hair), vitiligo (bright blue-white), porphyria urine fluorescence, Pseudomonas cues, and selected surgical margin/suture uses. Covers dark-room technique, fluorophore biology, colour→diagnosis map, false positives/negatives, and when KOH, culture, or porphyria labs must co ^[1]

Structured revision sheet

Must-know numbers and names

List every score, size threshold, dose, and time window from this topic on a blank page from memory, then check against the sections above.

Three classic MCQ angles

1. Most likely diagnosis given a vignette
2. Next best step in management
3. Most appropriate investigation

Three classic SAQ angles

1. Pathophysiology in five steps
2. Management algorithm with doses
3. Complications and prevention

Clinical station flow

Greet → focused history → targeted exam → investigations → explain diagnosis → emergency care → definitive plan → safety-net / follow-up → answer examiner questions on mechanism and pitfalls.

^{[1] [1] [1]}

References10ShowHide

1. [1]Asawanonda P, Taylor CR. Wood's light in dermatology Int J Dermatol, 1999.PMID 10583611
2. [2]Klatte JL, van der Beek N, Kemperman PM. 100 years of Wood's lamp revised J Eur Acad Dermatol Venereol, 2015.PMID 25428804
3. [3]Gomez-Martinez S, Ibaceta Ayala J, Morgado-Carrasco D. [Translated article] Wood's Light in Inflammatory and Autoimmune Dermatoses, Infections and Skin Cancer Actas Dermosifiliogr, 2025.PMID 39722344
4. [4]Kwaśny M, Stachnio P, Bombalska A. Application of Wood's Lamp in Dermatological and Dental Photodiagnostics Sensors (Basel), 2025.PMID 40968799
5. [5]Radhakrishnan S, Logamoorthy R, Karthikeyan K, et al. Erythrasma: a systematic review of interventions Clin Exp Dermatol, 2025.PMID 40635638
6. [6]Sun D, Lu J, Liu T, et al. Wood's lamp for early detection of Microsporum Canis tinea capitis in children Photodiagnosis Photodyn Ther, 2025.PMID 39638219
7. [7]Mayser P, Stapelkamp H, Krämer HJ, et al. Pityrialactone- a new fluorochrome from the tryptophan metabolism of Malassezia furfur Antonie Van Leeuwenhoek, 2003.PMID 14574113
8. [8]Prevost E. The rise and fall of fluorescent tinea capitis Pediatr Dermatol, 1983.PMID 6680181
9. [9]Nguyen K, Arora N, Ha O, et al. Utilizing Wood's Lamp to Demarcate Excisional Margins for Melanoma: A Retrospective Chart Review. Dermatol Surg, 2026.PMID 41033300
10. [10]Pan S, Ryan MP, Rapini RP. Erythrasma JAMA Dermatol, 2024.PMID 38231505