Erythrasma: Causes, Treatment & How to Tell It Apart from Jock Itch & Intertrigo
By ScanSkinAI Editorial Team✓ Reviewed for medical safetyLast updated June 2026
Erythrasma is the rash that won't quit — a brownish-red patch tucked into the groin, under the breasts, in the armpit, or between the toes that has been treated with three different antifungal creams without budging. The reason: it isn't a fungus. It's a slow-growing bacterial infection (Corynebacterium minutissimum) that needs an antibiotic, not an antifungal. The diagnostic giveaway is dramatic — a Wood's lamp turns the patch coral-red within seconds.
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Quick Answer
Erythrasma is a mild, long-lasting bacterial skin infection that causes reddish-brown patches in warm, moist skin folds like the groin, armpits, under the breasts, or between the toes. Because it looks like a standard fungal rash or jock itch, it is frequently treated with antifungal creams without success. Erythrasma is caused by bacteria, meaning it requires topical or oral antibiotics to clear. A doctor can easily confirm the diagnosis using a special UV light that makes the rash glow a distinctive coral-red colour.
Symptoms
- Well-defined brownish-red patches
- Fine, dry scale
- Sharp borders without central clearing
- Mild or no itch
- Located in groin, armpits, under breasts, or between 4th–5th toes
- Coral-red fluorescence under Wood's lamp
Severity & Progression
What Causes Erythrasma
Corynebacterium minutissimum is a Gram-positive bacterium that lives quietly on healthy skin. When the local environment becomes warm, moist, and occluded — a sweaty groin in summer, a sock-and-shoe foot all day, an inframammary fold in a humid climate — the bacterium overgrows in the upper layer of the epidermis (stratum corneum). It does not invade deeper, which is why erythrasma is usually painless and never produces pus or fever. The brown discolouration comes partly from inflammation and partly from porphyrins the bacterium secretes; those same porphyrins are what light up coral-red under a Wood's lamp and make diagnosis easy in seconds.
How Erythrasma Differs from Similar Conditions
Several conditions can look similar. Here's how to tell them apart — though a healthcare professional can provide a definitive diagnosis.
| Condition | Key Difference from Erythrasma |
|---|---|
| Tinea cruris (jock itch) | Active raised, scaly border with central clearing; itchier; KOH-positive; spares the scrotum. Erythrasma is uniformly brownish, flat, with sharp borders. |
| Candida intertrigo | Beefy-red, moist, with satellite pustules at the edge. Often itches and burns. Erythrasma has fine dry scale and no satellites. |
| Inverse psoriasis | Bright red, shiny, no scale; often involves the gluteal cleft and umbilicus too. Erythrasma is browner and finely scaly. |
| Seborrheic dermatitis (intertriginous) | Yellowish, greasy scale; often also affects scalp and face. Erythrasma is sharply demarcated and limited to folds. |
Treatment: What Actually Works
First-line (localised disease): Topical erythromycin 2% or clindamycin 1% solution/gel applied twice daily for 2 weeks clears most cases. Topical fusidic acid 2% cream is an alternative where available. A 5% benzoyl peroxide wash used in the shower for 5 days is a low-cost adjunct that works because of its antibacterial action.
Widespread or recurrent disease: Oral erythromycin 250 mg four times daily for 7–14 days, or a single 1 g dose of clarithromycin. Tetracyclines are alternatives in adults.
Interdigital (toe-web) erythrasma: Often coexists with tinea pedis. Treat with topical clindamycin or erythromycin AND keep the feet dry — moisture-wicking socks, alternating shoes daily, and a drying powder (aluminium chloride 20% or a simple antiperspirant) at bedtime.
Why antifungal creams 'almost work': Imidazoles such as clotrimazole and miconazole have weak anti-Corynebacterium activity, so the rash partially fades and then returns. If a 'fungal' rash in a fold has been treated three times without a real cure, request a Wood's lamp exam.
Preventing recurrence: Lose weight if relevant, manage diabetes, dry folds thoroughly after showering, switch to breathable cotton underwear, and use a 5% benzoyl peroxide wash once weekly long-term.
When Erythrasma Is Actually Something Else
See a clinician within 1–2 weeks if: the rash is painful, spreading rapidly, blistering, weeping pus, or accompanied by fever (suggests cellulitis or impetigo); the patch is asymmetric, has irregular dark pigmentation, or a single bump is growing within it (rule out melanoma in the groin or axilla); standard antibiotic treatment does not clear the rash in 3 weeks (consider mycosis fungoides, extramammary Paget's disease, or biopsy for inverse psoriasis). See a clinician urgently if you have diabetes and the rash is rapidly enlarging or has any necrotic (black) areas — Fournier's gangrene and necrotizing fasciitis can begin in the groin.
Erythrasma Across Skin Types and Hair Types
On lighter skin (Fitzpatrick I–III) erythrasma looks classically pink-brown to coral-red. On medium and deep skin tones (IV–VI) the patch often appears violaceous, slate-grey, or hyperpigmented brown rather than red, and clinicians less familiar with diverse skin can dismiss it as 'just dark skin in the fold' or post-inflammatory hyperpigmentation. The Wood's lamp test removes that ambiguity instantly: regardless of skin tone, true erythrasma fluoresces coral-red because the diagnosis depends on bacterial porphyrins, not on visible erythema.
Self-Care Tips
- Dry skin folds completely after showering or sweating
- Wear loose, breathable cotton clothing and underwear
- Alternate shoes daily; use moisture-wicking socks
- Use a 5% benzoyl peroxide wash 1–2 times per week to prevent recurrence
- Manage weight and blood-sugar control if applicable
When to See a Doctor
If a brownish-red rash in a skin fold hasn't cleared after 2 weeks of antifungal treatment, is spreading, is painful, or if you have diabetes — request a Wood's lamp examination and topical antibiotic treatment.
Frequently Asked Questions
What does erythrasma look like?
Erythrasma usually appears as well-defined, reddish-brown patches with a fine, dry scale. It typically lacks the intense itching or standard ring shape seen in fungal infections. You will almost always find it in skin folds where moisture gets trapped, such as the armpits, the groin, beneath the breasts, or between the fourth and fifth toes. The rash tends to grow slowly and remain relatively flat.
How do I know if it's erythrasma or jock itch?
It can be very difficult to tell them apart visually, which is why erythrasma is often misdiagnosed as jock itch. Erythrasma is bacterial, while jock itch is fungal. Erythrasma tends to be less itchy and features a more solid brownish-red colour without the raised, blistered edges typical of ringworm. If you have been using an antifungal cream for weeks with no improvement, you should ask a doctor to check for erythrasma.
Is erythrasma contagious or caused by poor hygiene?
Erythrasma is not considered highly contagious. The bacteria that cause it are actually part of the normal bacteria that live on everyone's skin. An infection happens when these bacteria overgrow due to trapped moisture and friction. While keeping skin folds clean and dry helps treat and prevent it, having erythrasma does not mean you are unclean. People with diabetes, obesity, or excessive sweating are simply more prone to these flare-ups.
How will a doctor test me for this rash?
The most common and fascinating way a doctor diagnoses erythrasma is by using a Wood's lamp in a darkened room. This is a special type of ultraviolet light. When shone on the rash, the bacteria produce a specific chemical that glows a bright, fluorescent coral-red colour. This near-instant test helps your doctor distinguish erythrasma from fungal infections or simple chafing, ensuring you get the correct antibiotic treatment.
How do you get rid of erythrasma?
Because erythrasma is a bacterial infection, it will not respond to over-the-counter antifungal creams. The standard treatment is a course of topical antibiotics, such as erythromycin or clindamycin, applied directly to the skin for a couple of weeks. If the rash is widespread or particularly stubborn, your doctor might prescribe an oral antibiotic pill. Keeping the affected area dry and well-ventilated is also crucial for fully clearing the infection.
What can I do to stop this rash from coming back?
The best way to prevent erythrasma is by minimising moisture and friction in your skin folds. Dry off thoroughly after showering, paying special attention to areas between the toes, under the arms, and in the groin. Wearing loose-fitting, breathable clothing and moisture-wicking socks can also help. If you have diabetes, keeping your blood sugar levels well-managed is an excellent defense, as high blood sugar can encourage bacterial overgrowth on the skin.
Is erythrasma dangerous if left untreated?
Erythrasma is not generally dangerous, but it can be annoying and persistent. If left untreated, the rash can slowly spread to other skin folds and become a long-term, chronic issue. In skin folds that remain constantly damp, the skin might break down or crack, which can sometimes allow secondary, more severe bacterial infections to take hold. It is always best to have persistent rashes evaluated rather than waiting for them to worsen.
How can ScanSkinAI help with a persistent groin or armpit rash?
ScanSkinAI can analyze a photo of your persistent rash and compare it against a vast database of skin conditions, including bacterial infections like erythrasma and fungal infections like jock itch. It acts as an accessible screening aid to help you understand possible causes when a rash doesn't improve with standard creams. However, AI cannot replace a medical diagnosis. You must see a healthcare professional for a confirmed diagnosis, Wood's lamp test, and correct prescription.
Related Conditions
Medical References
Information on this page is sourced from and verified against reputable medical resources:
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Medical Disclaimer: This information is for educational purposes only and is not intended as medical advice. The content on this page should not be used to diagnose or treat any health problem. Always consult with a qualified healthcare professional for proper medical evaluation, diagnosis, and treatment of your condition.