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Conditions · Dermatology

Dermatophytosis (tinea) and onychomycosis !

Common fungal infections of the skin, scalp and nails (ringworm, athlete's foot, jock itch, nail fungus) caused by fungi that feed on keratin.

Updated 2026-11-01

Structures involved

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Microorganisms that cause it

Why it happens

What it is

Superficial infections of keratinised tissue (stratum corneum, hair and nails) by dermatophyte fungi. They are named by site: tinea capitis, corporis, cruris, pedis, manuum and unguium (onychomycosis).

Who gets it

Among the most common infections in the world. In Colombia and other tropical countries heat and humidity favour tinea pedis, cruris and corporis; tinea capitis mainly affects school-age children, and onychomycosis increases with age and diabetes.

Causes

  • Trichophyton species (T. rubrum, T. mentagrophytes, T. tonsurans): the most common causes
  • Microsporum species (M. canis from cats and dogs), especially in tinea capitis
  • Epidermophyton floccosum (skin and nails, not hair)
  • Spread from person to person, from animals or from soil, and via shared towels, floors and combs

Risk factors

  • Heat, humidity, sweating and occlusive footwear
  • Communal showers, pools and contact sports
  • Diabetes, peripheral vascular disease and immunosuppression
  • Contact with infected pets or children
  • Older age and nail trauma (onychomycosis)

Pathophysiology

Dermatophytes produce keratinases that let them live on dead keratin; they rarely invade living tissue. The host inflammatory response at the edge of the colony produces an active scaly border while the centre clears, giving the ring shape. In the scalp they invade hair shafts; a strong inflammatory response can produce a boggy kerion.

Classification

  • Tinea capitis (scalp), including kerion
  • Tinea corporis (body) and tinea faciei
  • Tinea cruris (groin)
  • Tinea pedis (foot: interdigital, moccasin, vesicular) and tinea manuum (hand)
  • Tinea unguium/onychomycosis (nails)

Symptoms and signs

  • Itchy annular plaque with a raised, scaly, advancing border and central clearing (tinea corporis)
  • Red scaly patches in the groin that spare the scrotum (tinea cruris)
  • Itchy, macerated, cracked skin between the toes, especially the 4th web space, or dry scaling of the sole (tinea pedis)
  • Scaly patches of hair loss with broken hairs ('black dots') in a child, sometimes with a painful boggy mass and neck lymph nodes (tinea capitis, kerion)
  • Thickened, yellow-white, brittle nails lifting from the nail bed (onychomycosis)

Diagnosis

Clinical
Typical appearance and distribution. Topical corticosteroids can change the look ('tinea incognito').
Tests
KOH preparation of scale, hair or nail showing branching septate hyphae; fungal culture identifies the species. For onychomycosis, KOH, culture or PAS stain of nail clippings confirms it before long oral treatment. Wood lamp shows green fluorescence in some Microsporum scalp infections.
Imaging
Not needed.

Differential diagnosis

  • Nummular eczema and contact dermatitis
  • Psoriasis (also mimics onychomycosis)
  • Cutaneous candidiasis (involves the scrotum, has satellite pustules)
  • Pityriasis rosea and pityriasis versicolor
  • Alopecia areata, seborrhoeic dermatitis and trichotillomania (for tinea capitis)

Goal of treatment

Clear the fungus, relieve itch, prevent spread and recurrence, and protect high-risk feet (diabetes) from bacterial infection.

Treatment

Medical
Tinea corporis, cruris and pedis: topical antifungals (azoles such as clotrimazole or allylamines such as terbinafine), continued for 1–2 weeks after the skin clears.
Medical
Tinea capitis and most onychomycosis need oral antifungals (terbinafine, griseofulvin in children, itraconazole) because topicals do not penetrate hair or nail well; topical nail lacquers may help limited nail disease.
Follow-up
With long oral courses, liver function is checked where indicated and drug interactions are reviewed (azoles inhibit CYP3A4); nail cure takes months as the nail grows out.
Lifestyle
Keep skin dry, dry between the toes, change socks, use sandals in communal showers, do not share towels or combs; examine and treat pets and household contacts in tinea capitis.

Drugs for this condition

Complications

  • Bacterial cellulitis entering through fissures in tinea pedis, especially in diabetes
  • Scarring alopecia after kerion
  • Majocchi granuloma (deep follicular infection), often after topical steroids
  • Dermatophytid ('id') reaction: itchy eruption at a distant site
  • Pain, difficulty walking and ingrown nails from thick onychomycotic nails

Prognosis

Skin tinea responds well to treatment but recurs often if predisposing factors persist. Onychomycosis is slow to cure and relapses are common.

Prevention

  • Keeping feet and skin folds dry and wearing breathable footwear
  • Footwear in communal showers and not sharing personal items
  • Regular foot examination in people with diabetes

Test yourself

Think of the answer, then tap the question to see it.

What does a KOH preparation show in dermatophytosis?

Branching septate hyphae in skin scale, hair or nail.

Why does tinea capitis need oral rather than topical treatment?

Topical antifungals do not reach the fungus inside the hair shaft and follicle.

How is tinea cruris told apart from candidal intertrigo?

Tinea cruris usually spares the scrotum and has a scaly advancing edge; candidiasis involves the scrotum and has satellite pustules.

Why is tinea pedis important in a patient with diabetes?

Fissures between the toes are an entry point for bacterial cellulitis and diabetic foot infection.

What should be avoided on suspected tinea and why?

Topical corticosteroids alone, which mask the rash (tinea incognito) and can let the infection spread deeper.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Clinical Overview of Ringworm (Centers for Disease Control and Prevention (CDC), 2024); Tinea Infections (MedlinePlus (U.S. National Library of Medicine), 2024).

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Representative model, for educational purposes only.

Skin highlighted on the Durgical 3D model