What are the likely causes and recommended management for a painless, non‑itchy red rash in the axilla?

Red Rash Under Armpit (Non-Itchy, Non-Painful)

The most likely diagnosis is intertrigo, a superficial inflammatory dermatitis caused by skin-on-skin friction in body folds, which should be managed with moisture control, barrier protection, and treatment of any secondary bacterial or fungal infection. 1, 2

Primary Differential Diagnosis

The painless, non-itchy presentation in the axilla narrows the differential considerably:

• Intertrigo is the leading diagnosis—a superficial inflammatory dermatitis occurring on closely opposed skin surfaces from moisture, friction, and lack of ventilation, presenting as erythema with peripheral scaling 1, 2
• Erythrasma caused by Corynebacterium minutissimum commonly affects the axillae and presents as a red-brown patch that fluoresces coral-red under Wood's lamp examination 3
• Seborrheic dermatitis can affect intertriginous areas but typically causes scaling and some pruritus, making it less likely here 4, 5
• Atopic dermatitis usually spares the groin and axillary regions, which helps differentiate it from seborrheic dermatitis 4

Diagnostic Approach

Clinical Examination Features to Assess:

• Look for satellite lesions (small pustules at the periphery) which indicate secondary Candida infection 1
• Check for peripheral scaling at the borders of erythema, typical of intertrigo 1
• Assess for crusting or weeping, which suggests secondary bacterial superinfection with Staphylococcus or Streptococcus 6, 1
• Perform Wood's lamp examination if erythrasma is suspected—coral-red fluorescence confirms the diagnosis 3

When to Consider Testing:

• Potassium hydroxide (KOH) preparation if candidal intertrigo is suspected based on satellite lesions 1
• Bacterial culture if there is crusting, weeping, or treatment failure 1

Treatment Algorithm

First-Line Management (Uncomplicated Intertrigo):

• Minimize moisture and friction with absorptive powders (cornstarch) or barrier creams 2
• Recommend light, nonconstricting, absorbent clothing; avoid wool and synthetic fibers 2
• Advise showering after physical activity and thoroughly drying intertriginous areas 2
• Apply emollients liberally at least twice daily to prevent skin dehydration 6

Treatment of Secondary Infections:

If satellite lesions suggest Candida:

• Topical antifungals: nystatin, clotrimazole, ketoconazole, oxiconazole, or econazole 1
• Resistant cases: oral fluconazole 1

If crusting/weeping suggests bacterial infection:

• Topical mupirocin for mild cases 1
• Oral flucloxacillin for more extensive bacterial superinfection 6

If erythrasma is confirmed (coral-red fluorescence):

• Oral erythromycin 250mg four times daily for 14 days is the treatment of choice with cure rates up to 100% 3
• Alternative: topical clindamycin or Whitfield's ointment for localized disease 3

Important Clinical Pitfalls

• Do not overlook secondary bacterial infection, which commonly complicates intertriginous dermatitis and requires specific antibiotic therapy 6
• Bodily secretions (perspiration, urine, feces) exacerbate skin inflammation in these areas, so addressing hygiene and moisture control is essential 1
• The absence of itching does NOT rule out fungal infection—candidal intertrigo may present with minimal pruritus 1
• Erythrasma can coexist with dermatophyte or Candida infections, so consider combination therapy if initial treatment fails 3

When to Escalate Care

• Treatment failure after 1-2 weeks of appropriate first-line management warrants reassessment and possible culture 7
• Extensive crusting or severe bacterial superinfection may require systemic antibiotics and specialist referral 7
• Rapid spreading or systemic symptoms (fever, malaise) require urgent evaluation for deeper soft tissue infection 4