Erythrasma

Superficial bacterial skin infection that affects intertriginous (skin fold) areas.

Aetiology

  • Causative agent: Corynebacterium minutissimum
  • Risk factors:
    • Warm, humid environments
    • Excessive sweating (hyperhidrosis)
    • Obesity
    • Diabetes mellitus
    • Immunosuppression
    • Poor hygiene

Pathophysiology

  • Bacteria reside in the stratum corneum.
  • Produce porphyrins (coproporphyrin III) → coral-red fluorescence under Wood’s lamp.
  • Chronic infection especially in skin folds.

Clinical presentation

  • Brownish-red or reddish-brown macules/patches
  • Well-defined borders, fine scaling
  • Common locations:
    • Groin, inner thighs
    • Axillae
    • Inframammary area
    • Interdigital spaces (toes) → most common
  • Usually non-pruritic, mild itching possible
  • Chronic, slowly progressing
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Investigations

Clinical + Wood's lamp examination
  • Under Wood's lamp → coral-red fluorescence (hallmark)
  • Skin scraping/KOH: negative for fungi
  • Bacterial culture rarely needed
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Dermoscopy may show:
  • Fine white scales
  • Uniform brown pigmentation

Management

First-line:
  • Topical antibiotics:
    • Clindamycin
    • Erythromycin
    • Fusidic acid
    • Benzoyl peroxide 5% gel wash
Systemic therapy (for extensive or recurrent cases):
  • Erythromycin 250 mg 4x1 for 2-3 weeks
  • Clarithromycin 1 gram SD
General management:
  • Maintain hygiene
  • Keep skin dry
  • Weight control
  • Reduce sweating