Erythrasma

Overview

Erythrasma is a common, generally mild skin infection caused by a bacterium called Corynebacterium minutissimum, which normally lives on the skin. When conditions are warm and moist, the bacterium can overgrow in skin folds and cause flat, reddish-brown, slightly scaly patches.

It typically affects the groin, the armpits, the skin under the breasts, the folds of the abdomen, and the spaces between the toes. Because it appears in the same warm, moist folds as fungal infections, erythrasma is often mistaken for jock itch, ringworm, or inverse psoriasis. A simple light test usually distinguishes it, and it responds well to treatment.

Symptoms

Erythrasma usually causes patches that are more discolored than inflamed, and symptoms are often mild.

• Well-defined, flat patches that are pink at first and turn reddish-brown
• Fine scaling or a wrinkled, slightly cracked surface
• Mild itching or no symptoms at all
• Patches in the groin, armpits, under the breasts, or between the toes
• Between the toes, the skin may look macerated (soft and white) and peel

Unlike jock itch, the patches usually have a uniform color without a strongly raised, ring-shaped border. People with diabetes tend to have larger or more widespread patches.

Causes

Erythrasma develops when Corynebacterium minutissimum, a bacterium that is a normal part of the skin's surface community, multiplies excessively. This overgrowth is encouraged by warmth, moisture, and friction in skin folds.

The bacterium produces a substance (porphyrin) that gives the infection its characteristic coral-red glow under ultraviolet light, which doctors use to confirm the diagnosis. Erythrasma is not highly contagious, and it reflects local skin conditions more than person-to-person spread.

Risk Factors

• Living in a warm, humid climate
• Excessive sweating
• Being overweight, which deepens and moistens skin folds
• Diabetes, which is strongly associated with more extensive erythrasma
• Poor hygiene or prolonged dampness of the skin
• A weakened immune system or older age

Diagnosis

Erythrasma is frequently diagnosed at the bedside, and a simple test makes it easy to confirm.

• Wood's lamp examination: Under ultraviolet (Wood's) light, erythrasma patches glow a distinctive coral-red or pink color, which fungal infections do not.
• Skin scraping: Microscopic testing helps rule out a fungal cause when the diagnosis is unclear.
• Clinical examination: The flat, brown, sharply bordered patches in typical fold locations are characteristic.

Because diabetes is associated with erythrasma, a doctor may check blood sugar in people with widespread or recurrent disease.

Treatment

Erythrasma usually clears readily with antibacterial treatment and measures to keep the skin dry.

• Topical antibiotics or antiseptics: Creams such as clindamycin or erythromycin, or antibacterial washes containing benzoyl peroxide, applied to the patches.
• Oral antibiotics: A short course of a macrolide antibiotic such as erythromycin or clarithromycin for widespread or stubborn cases.
• Keeping skin dry: Drying the folds thoroughly and reducing moisture to prevent recurrence.
• Treating underlying factors: Managing diabetes and excess weight where relevant.

Prevention and Self-Care

• Keep skin folds clean and dry, drying carefully after washing
• Wear loose, breathable clothing and change out of damp or sweaty clothes
• Use an absorbent powder in areas prone to sweating
• Manage diabetes and body weight, which lower the risk of recurrence
• Wash regularly with an antibacterial soap if you are prone to erythrasma

When to See a Doctor

See a doctor if you have persistent reddish-brown patches in skin folds that do not clear with basic care, or if a rash treated as a fungal infection is not improving. A doctor can confirm erythrasma with a Wood's lamp and prescribe the right antibiotic. Anyone with diabetes who develops widespread or recurrent fold rashes should be evaluated, as this can be a sign that blood sugar needs better control.

Related Topics

Frequently Asked Questions

References

1. American Academy of Dermatology. Erythrasma.
2. MedlinePlus, U.S. National Library of Medicine. Erythrasma.
3. DermNet. Erythrasma.
4. Merck Manual Consumer Version. Erythrasma.