Erythrasma

Overview

Erythrasma is a common superficial skin infection caused by the gram-positive bacterium Corynebacterium minutissimum. It affects areas where skin touches skin, especially the groin, armpits, under the breasts and between the toes. The infection remains mainly within the stratum corneum, so systemic illness is uncommon and inflammation is often modest. ^{[1] [2]}

Warmth, moisture and friction alter the local skin environment and allow Corynebacterium to proliferate. The organism produces porphyrins that can fluoresce coral red under a Wood lamp, a useful bedside clue. The fluorescence may be absent after washing because porphyrins are water soluble, so a negative Wood lamp examination does not completely exclude the diagnosis. ^{[1] [2]}

Erythrasma matters less because it is dangerous and more because it is frequently misidentified. Patients may repeatedly use antifungal creams for a rash that is bacterial, or may have mixed infection with tinea or Candida. Correctly identifying the process can shorten treatment and also prompt attention to moisture, friction, diabetes and other recurrence factors. ^{[1] [2] [3]}

Symptoms and warning signs

Lesions are usually well-demarcated pink, tan, red-brown or brown patches with fine scaling and superficial fissures. Itching is often absent or mild, although irritation can occur in hot or sweaty conditions. Toe-web disease can coexist with maceration, odor or fungal infection. Widespread or recurrent disease is more common in people with metabolic or immune risk factors. ^{[1] [2]}

Erythrasma itself rarely causes an emergency. Rapidly spreading redness, severe pain, fever, marked swelling, pus, tissue breakdown or systemic illness should raise concern for cellulitis, abscess or another deeper infection rather than uncomplicated erythrasma. People with poorly controlled diabetes or significant immune suppression should have a lower threshold for medical assessment of worsening skin-fold infection. ^{[1] [2]}

Diagnosis

Diagnosis is often clinical, based on distribution and appearance. A Wood lamp can show coral-red fluorescence caused by bacterial porphyrins. This finding is highly suggestive when present, although recent washing can remove the fluorescent material. When the diagnosis remains uncertain, skin scrapings, microscopy, Gram stain or culture can help distinguish erythrasma from dermatophyte or Candida infection. ^{[1] [2]}

Clinicians also assess whether the rash is isolated or part of a broader intertrigo problem. Glucose testing may be considered in recurrent or extensive disease when diabetes is suspected. Toe-web disease sometimes warrants testing for fungal coinfection. Biopsy is rarely necessary, but pathology can demonstrate delicate bacterial rods and filaments in the cornified layer when other diagnoses are being considered. ^{[1] [2] [3]}

The main look-alikes are tinea cruris, tinea pedis, candidal intertrigo, inverse psoriasis, seborrheic dermatitis and irritant intertrigo. Tinea often has a more active border, Candida may show satellite lesions, and psoriasis tends to be smoother and more persistent. Because morphology overlaps, simple point-of-care testing can prevent months of ineffective therapy. ^{[2] [3]}

Causes, risk factors and clinical context

Risk is increased by warm humid climates, heavy sweating, obesity, diabetes, advanced age, occlusive clothing and reduced mobility or hygiene. None of these factors means a person will develop erythrasma, but they create the moist skin-fold environment in which the bacterium thrives. Recurrence is common unless both infection and local environmental factors are addressed. ^{[1] [2]}

Untreated lesions may persist for months or recur repeatedly. The infection usually remains superficial, but chronic toe-web disease can contribute to skin barrier breakdown. After effective therapy, discoloration may take longer to fade than active infection, so residual color does not always mean treatment failure. Reassessment is useful when scaling, fluorescence or symptoms persist. ^{[1] [2] [3]}

Complications and why the diagnosis matters

Complications are uncommon. The main practical problems are misdiagnosis, recurrence, mixed bacterial-fungal infection and secondary skin breakdown. In people with diabetes, toe-web fissures and maceration can become portals for more serious bacterial infection, which makes foot care and early recognition of cellulitis especially important. ^{[1] [2]}

Prognosis is excellent with appropriate therapy, but recurrence is frequent because the organism can recolonize skin folds. Long-term success depends on keeping folds dry, reducing friction, treating hyperhidrosis when appropriate and improving management of diabetes or obesity when those conditions are relevant. ^{[1] [2] [3]}

Treatment and management

Localized erythrasma is usually treated with a topical antibacterial or antiseptic agent. Options described in dermatology references include topical clindamycin, fusidic acid where available and benzoyl peroxide. More extensive disease can be treated with an oral antibiotic such as a macrolide or tetracycline-class agent, selected according to local practice, contraindications and antimicrobial stewardship. ^{[1] [2]}

Skin-fold care is central. Patients can gently cleanse and dry the area, change damp clothing, use breathable fabrics and reduce prolonged occlusion. Toe webs should be dried carefully. If fungal infection is also present, both processes may need treatment. Repeated antibiotic courses without attention to moisture and friction often lead to quick recurrence. ^{[1] [2] [3]}

Topical products can irritate already inflamed skin, and systemic antibiotics have drug interactions and adverse effects. Treatment should be reassessed if lesions do not improve as expected because persistent “erythrasma” may actually be psoriasis, tinea, Candida or another disorder. Antimicrobial use should be targeted rather than indefinite. ^{[1] [2]}

Follow-up, recovery and prevention

Improvement is expected over days to weeks, but pigmentation may persist longer. Recurrent disease should trigger a review of sweating, footwear, body-fold moisture, diabetes and possible coinfection. In toe-web disease, prevention may require alternating shoes, moisture control and treatment of any accompanying fungal infection. ^{[1] [2]}

Keeping susceptible folds dry is the most practical preventive measure. Weight management, breathable clothing, prompt changing of sweaty garments and good foot hygiene can help. Some people with frequent recurrence benefit from periodic antibacterial washes or other dermatologist-directed prevention strategies, balanced against irritation and microbiome disruption. ^{[1] [2] [3]}

Special situations and care pathway

Erythrasma can be more extensive in people with diabetes or immune compromise and may be difficult to distinguish from fungal intertrigo in darker skin tones when redness is subtle. Wood lamp examination can therefore be particularly helpful. Any painful, warm or rapidly spreading rash should be evaluated for deeper infection rather than assumed to be recurrent erythrasma. ^{[1] [2] [3]}

A practical pathway is to identify the fold distribution, look for fine scale and characteristic color, use a Wood lamp when available, test for fungus if morphology is mixed, choose topical or systemic antibacterial treatment based on extent and then address moisture and metabolic risk factors to reduce recurrence. ^{[1] [2]}

When to seek urgent medical care

Seek prompt medical care when a skin-fold rash becomes rapidly painful, hot, swollen or spreading; when fever or systemic illness appears; or when a person with diabetes develops a worsening foot or toe-web infection. Those features are not typical of uncomplicated erythrasma and may indicate cellulitis or another serious process. ^{[1] [2]}

Sources

1. DermNet — Erythrasma
2. DermNet — Erythrasma pathology
3. DermNet — Bacterial skin infections — Corynebacteria

This article is based on trusted medical sources and is awaiting clinician review. It is not a substitute for personalized medical advice.