What Is Erythrasma? Bacterial Skin Rash, Causes & Treatment Options

Erythrasma is a superficial bacterial skin infection that usually develops in warm, moist skin folds and causes well-defined brown, red-brown, pink-brown, tan-brown, or darker patches with fine scale.

It is caused by Corynebacterium minutissimum, not fungus by default. This page covers its appearance, common fold locations, moisture-related causes, risk factors, fungal and inflammatory mimics, Wood lamp findings, testing, treatment options, recurrence prevention, mistakes, and warning signs that need medical review.

Erythrasma as a Bacterial Skin-Fold Rash

Erythrasma is a superficial infection of the outer skin layer caused by Corynebacterium minutissimum, a bacterium that can overgrow where skin remains warm, damp, occluded, and rubbed.

The condition mainly affects intertriginous areas—places where skin touches skin—such as the groin, armpits, under the breasts, abdominal folds, buttock folds, and spaces between the toes.

Erythrasma is not the same as a deep bacterial infection such as cellulitis. It is often mild and chronic, but it can return when moisture, friction, toe-web dampness, diabetes, or another risk factor remains.

Because it resembles tinea, Candida, intertrigo, psoriasis, and contact dermatitis, the safest treatment begins with confirming the likely cause rather than repeatedly switching random creams.

What Erythrasma Looks and Feels Like on Skin

Erythrasma usually appears as a well-defined brown, reddish-brown, pink-brown, tan-brown, or darker patch with fine scale.

The surface may look dry, slightly wrinkled, or “cigarette-paper” thin. Symptoms are often mild: some people notice slight itching, burning, odor, or dampness, while others mainly notice discoloration.

Common Patch Features

Common features include a sharply outlined fold patch, fine scale, and mild itch or no itch.

• Brown, red-brown, pink-brown, tan-brown, or darker discoloration.
• Fine, dry scale rather than thick crust.
• Slow or chronic behavior rather than sudden rapid spread.
• Mild itch, irritation, or burning in some people.
• Possible dampness or odor where folds stay moist.
• Peeling, cracking, or maceration between the toes.
• One patch or several affected folds.

Signs That Suggest More Than Simple Erythrasma

Severe pain, rapid spread, fever, pus, open sores, red streaks, major swelling, blisters, or ulceration are not typical of uncomplicated erythrasma.

Those signs can indicate cellulitis, an abscess, another bacterial infection, severe intertrigo, or a different diagnosis that needs medical assessment.

Skin Areas Where Erythrasma Commonly Appears

Erythrasma usually appears where skin stays warm, damp, occluded, and rubbed together.

Common sites include groin folds, inner thighs, armpits, under the breasts, abdominal folds, the buttock fold, genital-adjacent creases, and spaces between the toes. Toe-web disease may be missed because it can look like ordinary peeling or athlete’s foot.

More than one site can be involved, especially when sweating, diabetes, obesity, reduced mobility, or persistent moisture affects several folds.

Why Erythrasma Develops in Warm Moist Folds

Erythrasma develops when Corynebacterium minutissimum overgrows in the outer skin layer under warm, moist, and occluded conditions.

How Corynebacterium Minutissimum Causes the Rash

Corynebacterium minutissimum can live on skin without causing symptoms, but moisture and friction make overgrowth more likely.

The bacteria remain mainly in the stratum corneum, the outermost skin layer. They produce porphyrins, including coproporphyrin III, which can create the characteristic coral-red or coral-pink Wood lamp glow.

Erythrasma can occur alone or coexist with dermatophyte fungus, Candida, or another fold disorder. That is why one treatment may fail when the rash is mixed.

Why Moisture, Heat, Friction, and Occlusion Matter

Dampness softens the skin surface, friction weakens the barrier, and occlusion traps heat and sweat.

Tight clothing, wet socks, poorly dried toe webs, occlusive footwear, deep folds, and humid weather can keep the environment favorable even after medicine clears the visible patch.

Risk Factors That Make Erythrasma More Likely

Erythrasma is more likely when folds remain damp, warm, occluded, or repeatedly irritated.

Risk factors do not prove the diagnosis, but they help explain recurrence and guide prevention.

• Heavy sweating or hyperhidrosis.
• Hot or humid climate.
• Diabetes or recurrent high-glucose concerns.
• Obesity or deep skin folds.
• Tight or non-breathable clothing.
• Poor drying after bathing.
• Occlusive shoes or damp socks.
• Persistent toe-web moisture.
• Older age or reduced mobility.
• Immune suppression.
• Repeated intertrigo or mixed bacterial-fungal infection.

A recurrent or widespread fold rash in someone with diabetes, immune suppression, poor circulation, or foot wounds deserves medical review rather than repeated self-treatment.

Conditions That Can Look Like Erythrasma

Erythrasma can resemble fungal rash, Candida, ordinary intertrigo, inverse psoriasis, product-related dermatitis, acanthosis nigricans, and cellulitis.

Erythrasma vs Fungal Rash

Tinea can affect the same warm folds and may cause scale, itching, or discoloration.

A more active scaly border can favor tinea, while erythrasma often has fine scale and brown-red discoloration. KOH microscopy can detect fungal elements when the visual pattern is not enough. Steroid-only cream can alter or worsen untreated fungal infection.

Erythrasma vs Candidal Intertrigo

Candidal intertrigo often looks wetter and brighter red and may have small satellite pustules outside the main rash.

Erythrasma is often drier, browner, and more finely scaly. The two can coexist, especially in moist folds, so mixed signs may require both bacterial and fungal assessment.

Erythrasma vs Inverse Psoriasis or Contact Dermatitis

Inverse psoriasis often creates smooth, shiny, sharply bordered fold plaques and may occur with psoriasis elsewhere or nail changes.

Allergic contact dermatitis or irritant dermatitis may follow deodorants, fragrances, wipes, fabrics, friction, or topical products and is often itchier. Neither diagnosis is confirmed by a coral-red bacterial fluorescence pattern.

Erythrasma vs Acanthosis Nigricans or Cellulitis

Acanthosis nigricans causes thicker, velvety darkening rather than a finely scaly infection.

Cellulitis is deeper, more acute, painful, warm, swollen, and spreading; fever or red streaks can occur. Those signs should not be managed as routine erythrasma.

Diagnosis Through Exam, Wood Lamp, and Testing

Erythrasma is often suspected from its location, color, fine scale, chronicity, and mild symptoms, but Wood lamp examination and fungal testing can make the diagnosis safer.

Why Wood Lamp Examination Is Useful

A Wood lamp uses long-wave ultraviolet light and may make erythrasma fluoresce coral-red or coral-pink.

The glow comes from bacterial porphyrins, especially coproporphyrin III. Recent washing can remove water-soluble porphyrin from the surface and reduce the glow, so a negative result does not always end the evaluation when the clinical pattern remains suspicious.

Wood lamp examination is painless and helps distinguish the bacterial pattern from many fungal-looking or inflammatory fold rashes.

When KOH, Culture, or Other Tests May Be Needed

KOH scraping is useful when tinea, Candida, athlete’s foot, or mixed infection may be present.

• Fungal microscopy or culture when fungal signs remain uncertain.
• Bacterial culture when pus, secondary infection, or treatment failure changes the picture.
• Diabetes assessment when recurrence, widespread disease, or other risk signs fit.
• Biopsy only rarely, when the rash is atypical or resistant and another condition is suspected.

What to Prepare for an Appointment

• When the rash first appeared and whether it keeps returning.
• Which areas are affected: groin, armpits, under breasts, belly fold, buttock fold, or toe webs.
• Itch, burning, pain, odor, dampness, cracking, peeling, pus, or open sores.
• Recent sweating, heat exposure, tight clothing, wet socks, or occlusive shoes.
• Diabetes history, high-glucose concerns, immune suppression, or repeated infections.
• History of athlete’s foot, toenail fungus, Candida, or intertrigo.
• Products already used, including deodorants, powders, antifungals, steroids, or antibiotics.
• Whether steroid cream made the rash worse or changed its appearance.
• Any prior Wood lamp, KOH, culture, or dermatologist diagnosis.

Treatment Options for Erythrasma

Erythrasma treatment usually combines appropriate antibacterial medicine with fold care that reduces moisture and recurrence.

The exact product, duration, and need for prescription treatment depend on location, extent, previous treatments, pregnancy, allergies, drug interactions, and certainty of diagnosis.

Topical Treatment for Localized Erythrasma

Localized erythrasma is often treated with a topical antibacterial option after the diagnosis is reasonably clear.

Options used in clinical care include topical erythromycin, clindamycin, mupirocin, fusidic acid where available, and benzoyl peroxide washes or gels in selected cases. A clinician or product label should guide the exact application plan.

Leftover antibiotics or repeated topical antibiotics should not be used blindly because a fungal, inflammatory, or mixed rash may require a different plan.

Oral Treatment for Extensive or Recurrent Erythrasma

Extensive, recurrent, or difficult disease may require clinician-directed oral treatment.

Oral macrolides such as erythromycin or clarithromycin may be considered, but pregnancy, allergies, liver disease, heart-rhythm risk, and medication interactions must be reviewed. The page does not provide antibiotic dosing.

When Antifungal Treatment Is Needed

Antifungal treatment is not the main treatment for pure erythrasma.

It may be needed when tinea, Candida, athlete’s foot, or a mixed bacterial-fungal infection is confirmed or strongly suspected. KOH testing helps prevent repeated antifungal use when the bacterial pattern is more likely.

Skin-Fold Care That Helps Prevent Recurrence

Erythrasma can return when sweat, friction, damp toe webs, or occlusive clothing recreate the same environment after treatment.

• Dry skin folds gently after bathing.
• Dry carefully between every toe.
• Wear breathable, loose clothing.
• Change sweaty clothing promptly.
• Rotate shoes and allow footwear to dry.
• Use clean moisture-wicking socks.
• Reduce rubbing in deep folds.
• Manage excessive sweating when relevant.
• Support diabetes care when applicable.
• Avoid harsh scrubbing and irritating fragranced products.
• Treat coexisting athlete’s foot or Candida when confirmed.

Recurrence and Treatment Failure Patterns

Erythrasma may recur because bacteria remain in damp folds, risk factors continue, treatment was incomplete, or the original rash was fungal, inflammatory, or mixed.

Common reasons include persistent sweating, damp toe webs, tight footwear, deep-fold friction, diabetes context, reinfection from wet clothing or shoes, and repeated steroid or antifungal treatment without confirmation.

When the rash returns quickly or never fully clears, the next step should be diagnostic reassessment—not simply another round of the same cream.

• Recheck all affected folds and toe webs.
• Review Wood lamp findings or repeat the examination when appropriate.
• Use KOH or fungal culture if tinea or Candida remains possible.
• Review adherence, moisture control, and product irritation.
• Assess diabetes, immune suppression, poor circulation, and foot wounds when relevant.

Erythrasma Treatment Mistakes to Avoid

The biggest erythrasma mistake is treating every fold rash as fungus without checking whether the pattern is bacterial, fungal, inflammatory, or mixed.

Do not over-scrub, bleach, peel, or apply multiple fragranced powders to irritated folds. Do not ignore diabetes, recurrent foot cracking, or repeated toe-web infection.

When a Skin-Fold Rash Needs Medical Review

A skin-fold rash should be checked when it is recurrent, rapidly spreading, painful, draining, cracked, ulcerated, treatment-resistant, or linked with fever, diabetes, immune suppression, pregnancy, poor circulation, or foot wounds.

Rash Signs That Need Evaluation

• Rapid spread or marked worsening.
• Severe pain or tenderness.
• Pus, drainage, open sores, or ulceration.
• Fever, red streaks, major warmth, or swelling.
• Bad odor with severe maceration.
• Cracking or bleeding between the toes.
• No improvement after appropriate treatment.
• Frequent recurrence in the groin, armpits, under breasts, abdominal folds, or toe webs.
• Worsening after steroid cream.

Patient Contexts That Need Extra Caution

Diabetes, immune suppression, poor circulation, recurrent infection, pregnancy, older age with reduced mobility, and foot wounds make a fold rash more important to assess.

Genital-adjacent pain, ulcers, discharge, open sores, or uncertain diagnosis also need clinical evaluation rather than repeated over-the-counter treatment.

Key Takeaways About Erythrasma

Erythrasma is a superficial bacterial rash of skin folds, so safe care depends on confirming the bacterial pattern, treating the actual cause, and reducing the moisture and friction that support recurrence.

• Erythrasma is caused by Corynebacterium minutissimum.
• It commonly affects the groin, armpits, under breasts, abdominal folds, buttock folds, and toe webs.
• Patches may look brown, red-brown, pink-brown, tan-brown, or darker with fine scale.
• A Wood lamp may show coral-red or coral-pink fluorescence.
• Tinea, Candida, intertrigo, psoriasis, dermatitis, and acanthosis nigricans are important mimics.
• Localized disease often uses topical antibacterial treatment.
• Extensive or recurrent disease may need clinician-directed oral treatment.
• Prevention focuses on drying folds, reducing friction, rotating footwear, and addressing sweating or diabetes context.
• Pain, pus, fever, spreading redness, ulcers, cracks, or treatment failure need medical review.

Frequently Asked Questions About Erythrasma

Sources & Evidence About Erythrasma