Erythrasma is a superficial skin infection caused primarily by the bacterium Corynebacterium minutissimum, a gram-positive, lipophilic, non-spore-forming bacillus that normally lives on the skin. The infection affects the uppermost layer of the skin and is characterised by well-defined patches, often in skin fold areas such as the groin, armpits, between the toes. Although often benign, erythrasma is clinically meaningful because it may mimic fungal or other skin diseases and may be persistent or recurrent.
Why Does Erythrasma Occur?
Erythrasma arises under conditions that allow C. minutissimum to overgrow in the skin's superficial layers. Under warm, humid, occluded, or moist environments, the organism proliferates more readily. Host factors further increase risk: people with diabetes mellitus, obesity, excessive sweating, older age, poor hygiene or immunocompromise are more prone. For example, excessive sweating, warm climate, poor hygiene, advanced age, obesity, and diabetes are key predisposing factors. The body-site factors are also relevant: skin folds and toe-web spaces have high moisture and occlusion, suitable for microbial growth. Once C. minutissimum invades the stratum corneum, it may dissolve keratin fibrils and produce porphyrins (notably coproporphyrin III) that can be used diagnostically. Erythrasma is more common in tropical and subtropical climates and may occur more frequently among persons in institutional settings.
How Does Erythrasma Present Clinically?
Clinically, erythrasma appears as gradually enlarging patches or macules in intertriginous or interdigital sites. The lesions are often pink-red when new, evolving to brownish or tawny with fine scaling, superficial fissuring or wrinkling. The borders are usually sharply demarcated from adjacent skin. The most common sites are toe-web spaces, groin, axillae, submammary folds, the intergluteal fold, or periumbilical skin in obese individuals. Symptoms are mild or absent in many cases; occasionally, slight pruritus or softening of the skin may occur.
In individuals with darker skin tones, the reddish component may not be obvious; the patch may appear as darker or violaceous rather than bright red. In rare cases, a more widespread or "generalised" variant may be seen, involving trunk or other sites beyond classic skin folds, particularly in diabetic or obese individuals. Because the appearance overlaps with fungal infections, candidiasis, or intertrigo, differential diagnosis is important.
How Is Erythrasma Diagnosed?
Diagnosis of erythrasma is primarily clinical, based on lesion appearance and risk factors, but can be aided by specific investigations. The distinctive feature is coral-pink fluorescence of lesions under a long-wave ultraviolet 365nm "Wood's lamp". This fluorescence occurs because C. minutissimum produces porphyrins (especially coproporphyrin III) that fluoresce.
Can the IBOOLO Dermatoscope be Used to Examine Erythrasma?
The IBOOLO DE-3100 PRO, DE-4100 PRO and the latest DE-500 model all feature a UV mode. These can be used to observe the fluorescence of erythrasma, aiding clinicians in making rapid diagnoses. The advantage of a dermatoscopy unit equipped with UV light compared to a traditional Wood's lamp lies in its use of a sophisticated combination of high-end optical lenses. This allows for a very clear observation of the fluorescent reaction through the viewing port. Furthermore, the dermatoscopy unit can be connected to a smartphone, making it extremely convenient to capture and save images of the fluorescent reaction.
365nm UV light, when used in dermatoscopy or Wood's lamp examination, is commonly used to observe the following types of conditions:
● Fungal Infections
•Tinea Capitis: Typically shows a bright green or faint green fluorescence.
•Tinea Versicolor: Usually displays a pale yellow or golden-yellow fluorescence.
● Bacterial Infections
•Erythrasma: Shows a characteristic coral-red fluorescence.
•Acne: Porphyrins—metabolic products of Cutibacterium acnes—can sometimes be observed as orange-red fluorescence within the hair follicles.
● Pigmentary Disorders
Wood's light helps to distinguish whether changes in pigmentation are in the epidermis or the dermis, or to help define the extent of pigment loss:
•Vitiligo: Due to the absence of melanocytes, the affected skin areas show a clearly demarcated, high-contrast bright white or milky-white fluorescence under the Wood's lamp.
●Melasma:
a. Epidermal type: The hyperpigmented area shows significantly enhanced contrast compared to the surrounding normal skin.
b. Dermal type: The contrast change is less noticeable.
What Treatment Options Exist for Erythrasma?
Treatment of erythrasma aims to eradicate the bacterial overgrowth, improve skin hygiene and dryness, and prevent recurrence. Topical therapies are first‐line for limited disease. Available options include topical fusidic acid, clindamycin solution, benzoyl peroxide, and Whitfield's ointment. A systematic review found that topical fusidic acid achieved faster symptom resolution, greater reduction in Wood's lamp fluorescence and fewer side-effects compared with clotrimazole.
For more extensive or recalcitrant disease, systemic antibiotics may be used—historically oral erythromycin (e.g., 250 mg four times daily for two weeks) showed high cure rates. Other systemic agents such as clarithromycin, tetracycline may be options; limited data exist. In conjunction, good skin hygiene, keeping skin folds dry, reducing sweating, weight reduction in obese individuals, and addressing co-morbidities (such as diabetes) are important. Recurrence is common unless underlying predisposing factors are addressed. As with any antibiotic therapy, attention to potential adverse effects, interactions, and suitability is important.