What is the most likely diagnosis and first‑line therapy for a red, scaly rash localized to the nasolabial folds that worsens with heat and sweating?

Seborrheic Dermatitis: Diagnosis and First-Line Treatment

The most likely diagnosis is seborrheic dermatitis, and first-line therapy consists of ketoconazole 2% cream applied once daily to the nasolabial folds for 2-4 weeks, combined with avoidance of heat triggers and alcohol-containing products. 1, 2, 3

Clinical Diagnosis

Seborrheic dermatitis presents as symmetric, well-demarcated, dull or yellowish-red patches with overlying adherent, greasy (not dry) yellowish scales in the nasolabial folds—a classic distribution for this condition. 4, 5 The worsening with heat and sweating is characteristic, as hypohidrosis from hyperkeratotic plugging of sweat ducts and thermodysregulation are recognized features. 6

The nasolabial fold location is pathognomonic, as seborrheic dermatitis characteristically affects areas rich in sebaceous glands including the nasolabial folds, glabella, eyebrows, and scalp. 7, 4, 8

First-Line Treatment Algorithm

Primary Antifungal Therapy

• Apply ketoconazole 2% cream once daily to affected nasolabial areas for 2-4 weeks until clinical clearing. 1, 2, 3 This addresses the underlying Malassezia yeast overgrowth that drives the greasy scaling and inflammation. 1, 9

Adjunctive Anti-Inflammatory Therapy

• For significant erythema and inflammation, add hydrocortisone 1% cream once or twice daily for short periods only (maximum 1-2 weeks). 1, 2 This is critical: only low-potency steroids should ever be used on facial skin, as medium- or high-potency agents (triamcinolone, mometasone, clobetasol) cause unacceptable skin atrophy and telangiectasia. 1

Essential Supportive Measures

• Avoid all alcohol-containing preparations on the face—these markedly worsen dryness and trigger flares. 1, 2
• Use tepid (not hot) water for cleansing, as hot water exacerbates symptoms. 1
• Apply fragrance-free moisturizers containing urea 10% or glycerin to damp skin after cleansing to restore barrier function. 1
• Avoid harsh soaps—use mild, pH-neutral (pH 5) non-soap cleansers or dispersible creams as soap substitutes to preserve natural skin lipids. 1, 2

Managing Heat and Sweating Triggers

Since this patient's rash worsens with heat and sweating:

• Recommend avoiding extreme temperatures and outdoor activities during hot periods. 6
• Suggest regular cooling measures including cold water sprays, fans, and air conditioning to manage thermodysregulation. 6
• Continue regular topical skincare as this may help reduce hyperkeratotic plugging of sweat glands. 6

Maintenance and Relapse Prevention

• After initial clearing, continue ketoconazole 2% cream once weekly as prophylactic maintenance to prevent relapse, which significantly reduces recurrence rates. 2
• Continue daily emollient use even when the condition appears controlled. 1

When to Refer to Dermatology

Refer if: 1, 4

• No clinical improvement after 4 weeks of appropriate first-line therapy
• Diagnostic uncertainty or atypical presentation
• Increased crusting, weeping, or pustules suggesting bacterial superinfection (treat with oral flucloxacillin if Staphylococcus aureus is suspected) 1
• Grouped vesicles or punched-out erosions suggesting herpes simplex superinfection (requires immediate oral acyclovir) 1

Critical Pitfalls to Avoid

• Never use medium- or high-potency topical corticosteroids on the face—the risk of atrophy, telangiectasia, and tachyphylaxis is unacceptably high. 1
• Do not use corticosteroids continuously beyond 2-4 weeks on facial skin, even low-potency agents. 1, 2
• Avoid greasy or occlusive products that can promote folliculitis. 1
• Do not confuse persistent mild itching after treatment with treatment failure—mild burning or itching from inflammation can persist for days after yeast elimination. 1