Erythrasma

Definition

• Erythrasma is a superficial bacterial skin infection typically found in skin folds (e.g. axillae, groin, interdigital spaces). It presents as hyperpigmented, thin patches that may be mistaken for fungal infections. Under a Wood’s lamp, erythrasma demonstrates a characteristic coral-pink fluorescence.

Aetiology & Causes

• Caused by Corynebacterium minutissimum (Gram-positive, non-spore-forming bacillus).

• Commonly misdiagnosed as tinea or candidal infection due to similar rash patterns.

Risk Factors

• Warm, humid climates

• Excessive sweating (hyperhidrosis)

• Skin of colour (hyperpigmentation more evident)

• Diabetes, obesity, poor hygiene

• Advanced age (compromised skin barrier)

Clinical Features

• Well-demarcated pinkish-brown patches with fine scaling; can sometimes have superficial fissures.

• Usually mildly pruritic or asymptomatic, though some patients report mild itch or discomfort.

• Common sites:

  • Axillae

  • Groin (inguinal folds)

  • Interdigital spaces (especially between the 4th and 5th toes)

  • Submammary folds in women

• May co-exist with fungal infections (e.g. tinea).

Diagnosis

• Wood’s Lamp Examination: Coral-pink fluorescence due to porphyrin production by C. minutissimum.

• Microscopy: Gram stain or methylene blue stain can identify C. minutissimum.

• Differential: Tinea cruris, intertrigo (candida), inverse psoriasis.

• Further Assessments: Check for underlying risk factors like diabetes if recurrent or extensive.

Management

Topical Treatment (First-Line)

• Fusidic Acid 2% Ointment BD for 2 weeks

• Whitfield’s Ointment (benzoic acid and salicylic acid) can also be used

• Alternatives: Topical clindamycin or erythromycin if fusidic acid is unavailable

Oral Treatment (If Extensive or Recurrent)

• Clarithromycin 1 g stat (single dose)

• Erythromycin or Tetracycline (doxycycline) for 7–14 days if needed

• Oral therapy is particularly beneficial in widespread disease or if topical therapy fails

Other Options

• Photodynamic Therapy (red light): Reported in some cases, though not routinely used in Australian practice

• Ensure adequate dryness of skin folds; consider antifungal if co-existing tinea

Prevention

• Antibacterial soaps or washes to reduce skin colonisation

• Keep skin folds dry (use absorptive powders, wear loose clothing)

• Repeat treatment or maintenance topical therapy if recurring

• Address underlying factors:

  • Weight reduction (if obesity)

  • Optimise glycaemic control in diabetes

  • Improve hygiene

Notes

• Erythrasma can recur, especially if risk factors (e.g. sweating, obesity, diabetes) are not addressed.

• Consider checking for co-infection with dermatophytes (tinea) as it may coexist in similar sites.

• Some guidelines suggest combining topical antibacterial with antifungal if diagnosis is uncertain.