Key Facts

Fungal skin infections are among the most common dermatological conditions globally. They range from superficial (dermatophytes, Candida, Malassezia) to deep/invasive (rare in immunocompetent hosts). Accurate diagnosis prevents inappropriate treatment (e.g. steroid misuse).

Epidemiology

• Dermatophyte infections: affect ~20–25% of the global population
• Tinea pedis (athlete's foot): most common dermatophyte infection
• Onychomycosis: ~10% of adults, increasing with age
• Candidal infections: common in diabetes, immunosuppression, obesity
• Pityriasis versicolor: common in young adults, especially in tropical/subtropical climates

Aetiology

• Dermatophytes: Trichophyton rubrum (most common), T. mentagrophytes, Microsporum canis, Epidermophyton floccosum
• Candida: C. albicans most common; C. auris emerging concern
• Malassezia: lipophilic yeast; part of normal flora; causes pityriasis versicolor
• Risk factors: warm/moist environment, occlusion, diabetes, immunosuppression, obesity, corticosteroid use

Pathophysiology

• Dermatophytes: keratinophilic — colonise stratum corneum, hair, and nails via keratinase enzymes
• Candida: disruption of skin barrier or altered mucosal flora → overgrowth → superficial or invasive infection
• Malassezia: converts from yeast to mycelial form → alters melanocyte function → hypo/hyperpigmentation

Dermatophyte Infections (Tinea)

• Tinea corporis: annular erythematous plaque with raised, scaly advancing edge and central clearing ('ringworm')
• Tinea pedis: interdigital maceration/scaling, moccasin-type scaling, vesicular
• Tinea cruris: erythematous scaly rash in groin/inner thighs; spares scrotum (unlike Candida)
• Tinea capitis: scaly scalp with hair loss ± kerion (boggy, painful mass); common in children
• Onychomycosis: distal/lateral subungual — yellow/white discolouration, thickening, onycholysis

Candidal Infections

• Intertrigo: erythema, maceration in skin folds; satellite papules/pustules
• Oral thrush: white plaques that can be scraped off; sore mouth
• Vulvovaginal candidiasis: pruritus, thick white discharge
• Balanitis: erythema, white plaques on glans
• Nail (candidal paronychia): painful, swollen nail fold

Pityriasis Versicolor (Malassezia)

• Hypo- or hyperpigmented, finely scaly macules/patches
• Trunk, upper arms, neck
• More visible after sun exposure (affected skin does not tan)

Red Flags

• Extensive or rapidly spreading infection in immunocompromised — consider invasive fungal disease
• Kerion (tinea capitis): painful, boggy mass — needs systemic antifungals + possibly steroids
• Steroid-modified tinea (tinea incognito): atypical appearance due to topical steroid misuse

Bedside

• Skin scraping: from active advancing edge; dissolve in 10–20% KOH → microscopy for hyphae/spores
• Wood's lamp: Microsporum species fluoresce green; erythrasma (Corynebacterium) fluoresces coral-red

Microbiology

• Fungal culture: skin/nail/hair sample on Sabouraud's agar — gold standard for species identification; takes 2–6 weeks
• Nail clippings: for suspected onychomycosis — confirm before systemic treatment

Bloods

• Not routinely required for superficial fungal infections
• LFTs: before systemic antifungals (terbinafine, itraconazole)
• Blood glucose/HbA1c: if recurrent candidiasis — screen for diabetes

Special Tests

• Dermoscopy: may show comma hairs in tinea capitis
• Fungal PCR: rapid identification available in some centres

Non-Pharmacological

• Hygiene advice: keep affected areas dry, avoid sharing towels/clothing
• Cotton clothing: reduce occlusion and moisture
• Weight management: reduce intertrigo risk

Pharmacological — Topical

• Clotrimazole 1% cream BD for 2–4 weeks: first-line for localised tinea, cutaneous candidiasis
• Miconazole 2% cream BD: alternative; available combined with hydrocortisone for inflamed infections (short-term only)
• Terbinafine 1% cream OD for 1–2 weeks: effective for localised dermatophyte infections
• Ketoconazole 2% shampoo: pityriasis versicolor — apply to affected areas, leave for 5 minutes, rinse; daily for 5 days
• Nystatin cream: specifically for Candida (not effective against dermatophytes)

Pharmacological — Systemic

• Terbinafine 250 mg OD: first-line systemic for dermatophyte infections
  • Tinea capitis: 4–6 weeks (Trichophyton), 6–8 weeks (Microsporum — may need higher dose)
  • Onychomycosis: 6 weeks (fingernails), 12 weeks (toenails)
• Itraconazole 200 mg OD or pulse dosing: alternative; better for Microsporum, Candida; check LFTs; many drug interactions (CYP3A4 inhibitor)
• Fluconazole 50 mg OD for 2–4 weeks: systemic Candida infections
• Griseofulvin: historically used for tinea capitis in children; being replaced by terbinafine

Referral Criteria

• Dermatology: diagnostic uncertainty, treatment failure, widespread/atypical infection
• Paediatrics: tinea capitis with kerion
• Infectious diseases: suspected deep/invasive fungal infection in immunocompromised

• Localised superficial infections: excellent response to topical antifungals
• Tinea capitis: good prognosis with systemic treatment; untreated may cause permanent scarring alopecia (kerion)
• Onychomycosis: cure rates ~70–80% with terbinafine; recurrence common (~20%)
• Candidal infections: good response to treatment; recurrence related to ongoing risk factors
• Pityriasis versicolor: responds to treatment but high recurrence rate (~60%); pigmentary change may persist for months
• Immunocompromised patients: may develop chronic, widespread, or invasive disease

Dermatophyte Infection Summary by Site

Antifungal Drug Summary