Erythrasma is a common bacterial skin infection caused by Corynebacterium species that live on the skin’s surface. It shows up as flat, brownish or pinkish patches in body folds and is frequently mistaken for a fungal infection like ringworm or athlete’s foot. That misdiagnosis matters, because antifungal creams won’t clear it, and the condition persists until the right treatment is used. Despite being widespread, erythrasma remains one of the more overlooked skin conditions in everyday clinical practice.
What Erythrasma Looks Like
Erythrasma appears as well-defined pink or brown patches with fine, dry scaling and sometimes shallow surface cracks called fissures.1PubMed. Erythrasma The patches tend to be flat and don’t have the raised, ring-shaped border you’d see with a typical fungal infection. In lighter skin, the color leans more toward pink or reddish-brown. On darker skin tones, erythrasma often looks tan to dark brown, which can make it blend in and go unnoticed for months or even years.
The most common locations are the armpits, groin creases, and the spaces between the toes. It can also show up in the fold under the breasts, between the buttocks, or around the navel.2PubMed. Erythrasma Most people with erythrasma have no symptoms at all, or at most mild itching. A case series of five adults with erythrasma in the armpits and groin found that four of the five were completely asymptomatic, with only one reporting moderate itchiness.3PubMed Central. Erythrasma – A Red Herring in the Ongoing Epidemic of Tinea That lack of discomfort is one reason the condition goes untreated so long.
Why It Keeps Getting Confused With Fungal Infections
Erythrasma’s biggest practical problem is that it looks a lot like tinea (ringworm) and other fungal skin infections. The scaly, discolored patches in skin folds could easily pass for jock itch or athlete’s foot, and many patients end up being prescribed antifungal creams that do nothing for a bacterial infection. One study described five adults whose erythrasma had been misdiagnosed as tinea and treated with antifungals, resulting in incomplete clearance that dragged on until the correct diagnosis was made.4PubMed Central. Erythrasma – A Red Herring in the Ongoing Epidemic of Tinea
The interdigital form, which lives in the toe web spaces, is especially prone to mix-ups. Research has confirmed that interdigital erythrasma is common and easily confused with interdigital tinea, and that it persists when not treated with the right class of medication.5PubMed. Interdigital erythrasma: clinical, epidemiologic, and microbiologic findings In children, the confusion gets even worse. Pediatric erythrasma between the toes can be mistaken for atopic eczema or a condition called juvenile plantar dermatosis, since doctors simply aren’t expecting a corynebacterial infection in a child.6PubMed Central. Interdigital Toe Web Space Erythrasma in a Young Child: A Case Report
Erythrasma can also coexist with fungal infections in the same skin fold, adding another layer of confusion. A person might truly have both a Candida or tinea infection and erythrasma at the same time, which means partial improvement on antifungals followed by lingering patches that won’t fully resolve. A standard potassium hydroxide (KOH) skin scraping, which is the quick in-office test for fungi, will come back negative for erythrasma because there are no fungal spores or hyphae to find.7PubMed Central. Erythrasma – A Red Herring in the Ongoing Epidemic of Tinea That negative fungal scraping should be a clue, but it often gets written off as a sampling error rather than prompting a reconsideration of the diagnosis.
The Coral-Red Glow That Gives It Away
The most reliable bedside test for erythrasma is a Wood’s lamp, which emits long-wave ultraviolet light. Under this light, erythrasma patches glow a distinctive coral-red or pinkish-orange color. The effect is striking enough that once you’ve seen it, the diagnosis is hard to miss.
That fluorescence comes from a specific molecule called coproporphyrin III, which the bacteria produce as a metabolic byproduct. Research using chemical analysis has confirmed that coproporphyrin III levels are clearly elevated in erythrasma lesions, while other porphyrins are diminished. The coproporphyrin III accumulates in the skin tissue and absorbs the UV light, then re-emits it at visible wavelengths, producing the coral-red glow.8PubMed. Exogenous coproporphyrin III production by Corynebacterium aurimucosum and Microbacterium oxydans in erythrasma lesions
There are a couple of catches. The fluorescence can wash away if you’ve recently bathed or scrubbed the area, because the porphyrins sit on the skin surface and are water-soluble. If a patient showers right before a clinic visit, the Wood’s lamp exam may be falsely negative. Newer diagnostic approaches are trying to work around this limitation. Ultraviolet-induced fluorescence dermoscopy, which combines a dermatoscope with UV light, has been used to detect the coral-red fluorescence alongside other features like brown scaling visible under polarized light.9PubMed Central. Erythrasma Mimicking Tinea Versicolor: The Diagnostic Utility of Ultraviolet-Induced Fluorescence Dermoscopy and Successful Combination Therapy This combined approach could help catch cases that a standard Wood’s lamp alone might miss.
Who Is Most Likely to Get It
Erythrasma thrives in warm, moist skin folds, so anything that creates or worsens that environment raises the risk. The two most consistent risk factors in the medical literature are diabetes and higher body weight. A study of patients with confirmed erythrasma found that about half were diabetic, and roughly two-thirds had a body mass index above 23.10PubMed Central. Clinical and epidemiological features of coryneform skin infections at a tertiary hospital An earlier investigation found an even stronger pattern: of 19 patients with extensive erythrasma, nearly half were diabetic, and most of those diabetic patients were also obese.11JAMA Dermatology. Erythrasma and Diabetes Mellitus
Beyond diabetes and weight, hot and humid climates push up rates of erythrasma by keeping skin folds perpetually damp. People who sweat heavily, wear tight-fitting synthetic clothing, or have skin-on-skin contact in deep folds are also at higher risk. Immunosuppression from medication or illness can tip the balance as well, since the bacteria that cause erythrasma are normal skin residents that only cause visible disease when conditions let them overgrow. Interestingly, the infection affects men and women at roughly equal rates.12PubMed Central. Clinical and epidemiological features of coryneform skin infections at a tertiary hospital
Treatment Options
Erythrasma generally responds well to treatment once the correct diagnosis is made. Options fall into two camps: topical creams applied directly to the patches, and oral antibiotics for more widespread or stubborn cases.
On the topical side, a systematic review covering studies from 1971 through 2024 found that both clotrimazole cream and fusidic acid cream are effective, but fusidic acid performed better overall. It provided faster symptom relief, a greater reduction in the coral-red fluorescence under Wood’s lamp, and fewer side effects compared to clotrimazole.13PubMed. Erythrasma: a systematic review of interventions Other topical antifungal creams with antibacterial crossover activity have also been tested. In one trial comparing two azole-type creams applied twice daily, cure rates exceeded 93% in both treatment arms.14PubMed. Double-blind comparison of the efficacy, toleration and safety of tioconazole base 1% and econazole nitrate 1% creams in the treatment of patients with fungal infections of the skin or erythrasma Clindamycin solution, Whitfield’s ointment (a benzoic and salicylic acid preparation), and sodium fusidate ointment are additional topical choices, sometimes used when first-line options don’t work or when the infection sits deep in a skin fold.15PubMed. Management of cutaneous erythrasma
For oral treatment, erythromycin has been the traditional go-to antibiotic. Clarithromycin, a newer macrolide antibiotic, offers the convenience of a single-dose regimen. A head-to-head comparison found that a single dose of clarithromycin worked faster than a course of erythromycin at the 48-hour mark, though both were equally effective by day 7 and day 14.16Taylor & Francis Online (Journal of Dermatological Treatment). A comparison between the effectiveness of erythromycin, single-dose clarithromycin and topical fusidic acid in the treatment of erythrasma The single-dose approach is appealing because it removes the compliance problem of remembering to take pills for a week or two.
When Antibiotics Stop Working
The bacteria behind erythrasma are developing resistance to commonly used antibiotics, and this is becoming a real clinical concern. Researchers in Turkey tested Corynebacterium minutissimum samples from erythrasma patients and found significant resistance to erythromycin, azithromycin, penicillin, and ampicillin.17Journal of the American Academy of Dermatology. Antibiotic susceptibility of Corynebacterium minutissimum isolated from lesions of Turkish patients with erythrasma This was prompted by the observation that some patients simply weren’t responding to erythromycin anymore.
A larger study from Iran painted an even more detailed picture. The highest resistance rate was to penicillin, at about 76% of isolates. Resistance to erythromycin and clarithromycin, the two macrolide antibiotics most commonly prescribed for erythrasma, was found in roughly 39% of isolates. Resistance to clindamycin was about 30%, to tetracycline about 24%, and to gentamicin and neomycin about 20%.18PubMed Central. The Prevalence and Antibiotics Susceptibility Patterns of Corynebacterium minutissimum Isolates from Skin Lesions of Patients with Suspected Erythrasma from Tabriz, Iran Genetic analysis showed that resistance to erythromycin was mainly linked to a specific resistance gene called ermX, found in 75% of resistant isolates.19PubMed Central. The Prevalence and Antibiotics Susceptibility Patterns of Corynebacterium minutissimum Isolates from Skin Lesions of Patients with Suspected Erythrasma from Tabriz, Iran
What this means for you practically: if you’ve been prescribed erythromycin or clarithromycin for erythrasma and it hasn’t cleared after a full course of treatment, resistance may be the reason. Switching to a topical agent like fusidic acid, or trying a different class of antibiotic, is a reasonable next step. The resistance data also reinforces why topical treatment is often preferred for localized disease. Slathering on a cream targets the bacteria directly without relying on systemic antibiotic levels and puts less selective pressure toward resistance.
Why It Keeps Coming Back
One of the most frustrating things about erythrasma is its tendency to recur. Even after a successful course of treatment that clears the patches completely, the infection often returns within weeks or months.20PubMed. Erythrasma This makes sense when you understand the underlying biology: the Corynebacterium species that cause erythrasma are normal residents of human skin. You can knock down their numbers with antibiotics, but you can’t sterilize the skin permanently. The moment conditions favor overgrowth again, the patches reappear.
Preventive strategies focus on making the skin environment less hospitable to bacterial overgrowth. Using antibacterial soap in the affected areas can help keep the bacterial population in check.21PubMed. Erythrasma Keeping skin folds dry is equally important. Thoroughly drying between the toes and in the groin and armpit creases after bathing, wearing breathable fabrics, and using absorbent powders in skin folds during warm weather all reduce the moisture that feeds bacterial growth. For people who have repeated flare-ups, intermittent use of a topical antibacterial agent has been recommended for both treatment and prevention.22PubMed. Management of cutaneous erythrasma
If you have diabetes, getting blood sugar under better control may reduce your risk of recurrence, given the strong association between erythrasma and poorly controlled diabetes. Similarly, weight loss that reduces the depth and moisture of skin folds can make a real difference, though this is easier said than done.
Related Skin Conditions From the Same Bacteria
Corynebacterium species don’t just cause erythrasma. They’re also responsible for two other skin conditions that can show up at the same time: trichomycosis axillaris, which produces waxy, yellowish coatings on armpit or pubic hair, and pitted keratolysis, which creates small crater-like pits on the soles of the feet. These three conditions have been described as a “corynebacterial triad,” and finding one should prompt a check for the others.23Journal of the American Academy of Dermatology. Coexistent erythrasma, trichomycosis axillaris, and pitted keratolysis: an overlooked corynebacterial triad?
Pitted keratolysis is worth knowing about because it’s another condition that often gets blamed on fungus. The characteristic shallow pits on the weight-bearing areas of the foot, combined with a noticeable odor, frequently get misdiagnosed as athlete’s foot. And trichomycosis axillaris, while cosmetically annoying, is usually harmless and can be treated simply by shaving the affected hair and applying a topical antibiotic. If you’ve been told you have one of these conditions, it’s worth asking whether erythrasma might also be present in your skin folds, since the same bacterial family is driving all three.
Red Light Therapy as an Experimental Alternative
Here’s where the biology behind erythrasma’s diagnosis circles back in an unexpected way. The same porphyrins that make erythrasma glow under Wood’s light can also be weaponized against the bacteria. When porphyrins absorb certain wavelengths of visible red light, they generate reactive oxygen molecules that damage the bacterial cells producing them. This is the principle behind photodynamic therapy.
Preliminary clinical work tested red light irradiation on erythrasma patients without adding any external photosensitizing drugs, relying entirely on the porphyrins the bacteria were already producing. Three patients achieved complete clearance, and most others saw their lesion area shrink by an average of about 29% after a single session. The treatment was well tolerated with no significant side effects.24PubMed. Photodynamic action of red light for treatment of erythrasma: preliminary results
These are early results from a small study, so red light therapy isn’t a standard recommendation yet. But the concept is elegant and the approach could become useful for patients who have antibiotic-resistant erythrasma or who want to avoid repeated courses of antibiotics. Since the bacteria are essentially manufacturing their own destruction when exposed to the right light, resistance is theoretically much harder to develop than it is for conventional antibiotics. Whether this pans out in larger trials remains to be seen, but it represents one of the more creative angles in treating what most people still think of as a simple rash.