Overview
Fungal Skin Infections (Tinea / Dermatophytosis)
1. Clinical Overview
Summary
Dermatophyte infections (Tinea) are superficial fungal infections of the skin, hair, and nails caused by organisms of the genera Trichophyton, Microsporum, and Epidermophyton. They are extremely common worldwide. The clinical name indicates the body site affected: Tinea Corporis (body - "Ringworm"), Tinea Pedis (feet - "Athlete's Foot"), Tinea Capitis (scalp), Tinea Cruris (groin - "Jock Itch"), Tinea Unguium/Onychomycosis (nails), Tinea Manuum (hands), and Tinea Faciei (face). Diagnosis is usually clinical, with skin scrapings for microscopy and culture confirming the diagnosis. Treatment depends on the site: Topical antifungals (Terbinafine, Clotrimazole) for most skin infections; Oral antifungals (Terbinafine, Itraconazole, Griseofulvin) required for scalp and nail infections. [1,2]
Clinical Pearls
"Ringworm" = Tinea, Not a Worm: The name comes from the classic annular (ring-shaped) rash with active, scaling edge and central clearing.
Tinea Capitis = Oral Antifungals Only: Topical treatments DO NOT penetrate the hair follicle. Oral Terbinafine or Griseofulvin is required.
Kerion = Urgent: A kerion is an inflammatory, boggy mass on the scalp caused by vigorous immune response to dermatophyte. Needs oral antifungals ± steroids (to reduce scarring alopecia).
Tinea Incognito: Tinea treated with topical steroids becomes modified (less typical appearance), making diagnosis difficult.
2. Epidemiology
Incidence
- Prevalence: Very common. One of the most common infectious skin diseases worldwide.
- Tinea Pedis: Most common dermatophyte infection in adults (~15-25% prevalence).
- Tinea Capitis: Most common dermatophyte infection in children. Highly contagious. Often in schools/nurseries.
Causative Organisms
| Organism | Route | Common Infections |
|---|---|---|
| Trichophyton rubrum | Anthropophilic (Human) | Most common overall. Tinea Pedis, Tinea Corporis, Onychomycosis. |
| Trichophyton tonsurans | Anthropophilic | Tinea Capitis (UK/USA – now most common cause). |
| Microsporum canis | Zoophilic (Animal – Cat/Dog) | Tinea Capitis (esp. Europe), Tinea Corporis. Fluoresces under Wood's Lamp. |
| Epidermophyton floccosum | Anthropophilic | Tinea Cruris, Tinea Pedis. |
| Trichophyton verrucosum | Zoophilic (Cattle) | Farmer's Ringworm. Often inflammatory (Kerion). |
Risk Factors
| Factor | Notes |
|---|---|
| Warm, Moist Environment | Occlusive footwear, gym, swimming pools. |
| Close Contact | Schools, sports (Wrestling "Herpes Gladiatorum" – but also Tinea). |
| Animal Contact | Pets (Cats, Dogs – Microsporum canis). Cattle (Trichophyton verrucosum). |
| Immunocompromise | Extensive or refractory infections. |
| Diabetes Mellitus | Increased susceptibility. |
| Obesity | Skin folds – Tinea Cruris. |
3. Pathophysiology
Mechanism of Dermatophyte Infection
- Contact with Fungal Elements: Spores (arthrospores) from infected humans, animals, or fomites (e.g., towels, combs).
- Adhesion to Keratinocytes: Dermatophytes have keratinases that allow them to adhere to and penetrate stratum corneum.
- Keratin Digestion: Fungi use keratin as a nutrient source. They digest keratin in skin, hair, and nails.
- Superficial Invasion: Infection remains superficial (epidermis, hair shaft, nail plate). Does not invade deeper dermis or blood (unless immunocompromised).
- Host Immune Response: Inflammatory response causes scaling, erythema. If vigorous (esp. zoophilic organisms) → Kerion formation.
- Clinical Manifestation: Annular lesions (outward growth with central healing), scaling, pruritus.
4. Clinical Presentations by Site
Tinea Corporis (Body – "Ringworm")
- Appearance: Annular (Ring-Shaped) erythematous plaque. Active, raised, scaly edge. Central clearing.
- Sites: Any body surface.
- Symptoms: Pruritic.
- DDx: Nummular eczema, Psoriasis, Pityriasis Rosea, Granuloma Annulare.
Tinea Pedis (Feet – "Athlete's Foot")
| Pattern | Description |
|---|---|
| Interdigital | Most common. Macerated, fissured skin between toes (esp. 4th-5th web space). |
| Moccasin | Chronic. Diffuse scaling and hyperkeratosis of soles, extending to sides of feet. Often bilateral. |
| Vesicular/Bullous | Inflammatory. Vesicles/Blisters on sole/instep. |
- Symptoms: Itchy. Fissures can be painful. Secondary bacterial infection possible.
- DDx: Eczema (contact dermatitis), Psoriasis (palmoplantar).
Tinea Capitis (Scalp – Children)
- Appearance: Patches of Alopecia (hair loss) with Scaling. Broken hairs ("Black Dot" pattern if T. tonsurans). May have mild inflammation or severe (Kerion).
- Kerion: Boggy, painful, pus-discharging mass. Intense inflammatory reaction. Risk of Scarring Alopecia. Not an abscess (don't incise).
- Demographics: Primarily children. Common in Afro-Caribbean children (UK).
- DDx: Alopecia Areata (smooth, no scaling), Seborrhoeic Dermatitis (cradle cap), Psoriasis.
- Wood's Lamp: Microsporum spp. may fluoresce green. Trichophyton tonsurans does NOT fluoresce.
Tinea Cruris (Groin – "Jock Itch")
- Appearance: Erythematous, scaly plaques in groin folds. Extends onto inner thighs. Spares scrotum (distinguishes from Candida which involves scrotum).
- Demographics: Adolescent/Adult males.
- DDx: Candida intertrigo (involves scrotum, satellite lesions), Erythrasma (coral-red fluorescence under Wood's lamp), Inverse Psoriasis.
Tinea Unguium / Onychomycosis (Nails)
| Pattern | Description |
|---|---|
| Distal/Lateral Subungual (DLSO) | Most common. Starts at free edge/lateral nail fold. Thickening, Discolouration (Yellow/White), Onycholysis (separation), Subungual debris. |
| Superficial White (SWO) | White, chalky surface. Easily scraped off. |
| Proximal Subungual (PSO) | Rare. Starts at cuticle. Consider immunocompromise (HIV). |
| Total Dystrophic | Entire nail destroyed. |
- Demographics: Increases with age. Toenails > Fingernails.
- DDx: Psoriatic nail dystrophy, Trauma, Lichen Planus.
Tinea Manuum (Hands)
- Appearance: Usually unilateral. Diffuse scaling of palm. "Two Feet, One Hand Syndrome" (bilateral Tinea Pedis + unilateral Tinea Manuum).
- DDx: Contact dermatitis, Psoriasis.
Tinea Faciei (Face)
- Appearance: Annular or serpiginous erythematous patches on face.
- Often Misdiagnosed: Eczema, Rosacea, Lupus. "Tinea Incognito" if steroids applied.
5. Investigations
Clinical Diagnosis
- Often clinical diagnosis is sufficient for typical presentations.
Skin Scrapings (Mycology)
| Test | Method | Notes |
|---|---|---|
| KOH Microscopy | Scrape active edge of lesion onto slide. Add 10-20% KOH. Look for hyphae under microscope. | Rapid (same day). Sensitivity 70-80%. |
| Fungal Culture (Sabouraud's Agar) | Skin/Nail/Hair sample onto culture medium. Takes 2-4 weeks to grow. | Gold standard for species identification. Essential for treatment failure. |
Hair Sampling (Tinea Capitis)
- Brushing/Plucking: Collect broken hairs and scale from scalp for microscopy and culture.
Wood's Lamp (UV Light)
- Uses: Microsporum species fluoresce Green. Helps distinguish from non-dermatophyte causes.
- Limitations: Trichophyton tonsurans (now most common Tinea Capitis in UK) does NOT fluoresce.
6. Management
Management Algorithm
SUSPECTED TINEA
(Annular Rash, Scaling, Pruritus)
↓
CLINICAL ASSESSMENT
(Site, Extent, Severity)
↓
CONFIRM DIAGNOSIS IF UNCERTAIN
(Skin Scrapings – KOH / Culture)
↓
TREATMENT BY SITE
┌─────────────────────────────────────────────┐
│ │
SKIN ONLY SCALP / NAILS
(Corporis, Pedis, (Capitis, Unguium)
Cruris, Manuum, Faciei)
↓ ↓
TOPICAL ANTIFUNGAL ORAL ANTIFUNGAL
(Terbinafine 1% Cream BD (Topicals don't penetrate)
OR Clotrimazole 1% Cream BD)
for 2-4 weeks TINEA CAPITIS:
↓ - Terbinafine PO 4-6 weeks
IF EXTENSIVE / RESISTANT: - OR Griseofulvin PO 6-8 weeks
→ Add Oral Antifungal + Ketoconazole SHAMPOO
(Reduce spore shedding)
↓
TINEA UNGUIUM:
- Terbinafine PO 3mo (finger)
/ 6mo (toe)
- OR Itraconazole Pulse
- Check LFTs if prolonged use
↓
KERION (Scalp):
- Oral Antifungal + Short Course Prednisolone
(Reduce inflammation to prevent scarring alopecia)
- DO NOT INCISE (Not an abscess)
Topical Antifungals (For Skin Infections)
| Agent | Formulation | Duration |
|---|---|---|
| Terbinafine 1% Cream | Apply BD | 1-2 weeks (often sufficient) |
| Clotrimazole 1% Cream | Apply BD | 2-4 weeks |
| Miconazole 2% | Apply BD | 2-4 weeks |
| Ketoconazole Cream | Apply OD-BD | 2-4 weeks |
Oral Antifungals (For Scalp, Nails, Extensive/Refractory Skin)
| Agent | Indication | Duration | Notes |
|---|---|---|---|
| Terbinafine | Tinea Capitis (Trichophyton), Onychomycosis, Extensive skin | 4-6 weeks (Capitis), 6 weeks-6 months (Nails) | LFT monitoring for prolonged use. Drug interactions (CYP2D6). |
| Itraconazole | Tinea Capitis (Microsporum), Onychomycosis | Pulse therapy for nails (1 week per month x 2-3 cycles) | LFT, Cardiac caution. |
| Griseofulvin | Tinea Capitis (esp. Microsporum) | 6-8 weeks | Older drug. Still used for Microsporum. Teratogenic. |
| Fluconazole | Alternative | Variable | Less commonly used for dermatophytes. |
Adjunctive Measures
- Ketoconazole 2% Shampoo (Nizoral): For Tinea Capitis – reduces spore shedding. Apply twice weekly.
- Hygiene: Wash towels, bedding. Don't share combs/brushes. Treat pets if animal source.
- Shoes/Socks: Cotton socks. Rotate footwear. Antifungal powder for shoes.
7. Complications
| Complication | Notes |
|---|---|
| Scarring Alopecia | From Kerion if not treated promptly. |
| Secondary Bacterial Infection | Esp. fissures of Tinea Pedis (Cellulitis). |
| "Id" Reaction (Dermatophytid) | Allergic reaction to dermatophyte antigens. Vesicular rash on hands/feet distant from infection site. Treat the primary infection. |
| Recurrence | Common if hygiene measures not followed or source not treated. |
| Tinea Incognito | Modified appearance due to topical steroid use. May flare when steroids stopped. |
8. Differential Diagnosis
| Condition | Key Features |
|---|---|
| Tinea Corporis | Annular, scaly edge, central clearing. |
| Nummular Eczema | Coin-shaped, itchy. No central clearing. No active edge. |
| Psoriasis | Well-demarcated, silvery scale. May have nail pitting, other sites. |
| Pityriasis Rosea | "Herald patch" followed by secondary rash. Christmas tree pattern. |
| Granuloma Annulare | Annular papules. No scale. |
| Erythrasma | Brown/Red patches in flexures. Coral-red fluorescence on Wood's lamp. |
| Candida Intertrigo | Involves scrotum (Tinea Cruris spares it). Satellite lesions. |
9. Prognosis and Outcomes
- Tinea Corporis/Pedis/Cruris: Excellent prognosis with topical treatment.
- Tinea Capitis: Requires oral treatment. Usually cures. Kerion may leave scarring.
- Onychomycosis: Challenging. Oral treatment has ~70-80% cure rate (Toenails harder to cure). Recurrence common.
10. Evidence and Guidelines
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Tinea Capitis | BAD (British Association of Dermatologists) | Oral antifungals (Terbinafine or Griseofulvin). Adjunctive antifungal shampoo. |
| Fungal Skin Infections | NICE CKS | Topical for skin; Oral for scalp/nails. |
11. Patient and Layperson Explanation
What is Ringworm (Tinea)?
Ringworm is a fungal infection of the skin. Despite its name, it is NOT caused by a worm – the name comes from the ring-shaped rash it can cause. It is very common and usually easy to treat.
How did I get it?
It spreads by direct contact with infected people, animals (especially cats and dogs), or objects like towels and combs. Warm, moist environments like gyms and swimming pools increase the risk.
How is it treated?
- Skin infections: Antifungal cream (like Terbinafine or Clotrimazole) applied twice daily for 2-4 weeks.
- Scalp or Nail infections: Antifungal tablets are needed because creams cannot penetrate deeply.
Is it contagious?
Yes. Avoid sharing towels, clothes, and combs. If a pet is the source, have them checked and treated by a vet.
12. References
Primary Sources
- British Association of Dermatologists. Guidelines for the Management of Tinea Capitis. 2014.
- NICE Clinical Knowledge Summaries. Fungal Skin Infections. 2023.
13. Examination Focus
Common Exam Questions
- Classic Appearance: "Annular rash with active scaling edge and central clearing. Diagnosis?"
- Answer: Tinea Corporis (Ringworm).
- Tinea Capitis Treatment: "Why can't you use topical antifungals for scalp ringworm?"
- Answer: Topicals don't penetrate the hair follicle. Oral antifungals (Terbinafine, Griseofulvin) are required.
- Kerion Management: "Child with painful, boggy scalp mass. Diagnosis? Should you incise it?"
- Answer: Kerion (inflammatory Tinea Capitis). NO incision (not an abscess). Treat with oral antifungals ± short course steroids.
- Tinea Cruris vs Candida: "How to differentiate?"
- Answer: Tinea Cruris spares the scrotum; Candida intertrigo involves the scrotum and has satellite lesions.
Viva Points
- Wood's Lamp: Microsporum fluoresces green; Trichophyton tonsurans does not.
- "Two Feet, One Hand": Bilateral Tinea Pedis + Unilateral Tinea Manuum = classic pattern.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.