Dermatophyte Infections

Dermatophyte infections (dermatophytoses, commonly called ringworm or tinea) are superficial fungal infections of keratinised tissue — skin, hair, and nails — caused by a group of keratin-digesting fungi. They are among the most common human infections worldwide and are typically confined to the body's surface.

Definition

A dermatophyte infection is a superficial mycosis of keratinised tissue (stratum corneum, hair, or nail) caused by dermatophyte fungi — historically classified in the genera Trichophyton, Microsporum, and Epidermophyton — which can metabolise keratin.

Scope

This topic covers the dermatophyte fungi, the keratin-restricted nature of the infections they cause, the body-site nomenclature of tinea, the main routes of transmission, and the broad global burden. It is reference material describing how the disease group is classified and studied, and does not provide diagnostic or treatment instructions.

Key concepts

• Keratinophilic, keratin-digesting fungi
• Tinea nomenclature by body site (corporis, pedis, capitis, unguium, cruris)
• Trichophyton, Microsporum, Epidermophyton
• Anthropophilic, zoophilic, and geophilic sources
• Confinement to non-living keratinised tissue
• Molecular reclassification of dermatophyte taxonomy

Mechanisms

Dermatophytes colonise and digest keratin in the dead, keratinised layers of skin, hair, and nail, generally without invading living tissue, which limits most infections to the surface and shapes their inflammatory pattern. Infections are named by body site — for example tinea corporis (body), tinea pedis (feet), tinea capitis (scalp), tinea unguium (nail), and tinea cruris (groin). The source of the organism — human (anthropophilic), animal (zoophilic), or soil (geophilic) — influences transmission and the host inflammatory response. Molecular phylogenetics has substantially revised the traditional genus- and species-level classification of these fungi.

Clinical relevance

Dermatophytoses are extremely common and are mostly superficial, but their nomenclature and transmission patterns are relevant to clinical recognition and public-health reasoning. This entry describes how the infections are categorised and studied; it is reference material and not a basis for individual diagnosis or therapy.

Epidemiology

Dermatophyte infections affect a very large share of the world's population, with skin and nail involvement estimated in the hundreds of millions to over a billion people, making them among the most prevalent human infections. Distribution of species and clinical patterns varies by geography, climate, age, and contact with animals.

History

Dermatophytes were among the earliest microorganisms shown to cause human disease, with mid-nineteenth-century work linking fungal elements to skin and scalp infections, an important step in establishing the microbial basis of disease. The classical division into Trichophyton, Microsporum, and Epidermophyton has more recently been reorganised using multilocus molecular phylogenetics.

Debates

How should dermatophytes be classified?

Molecular phylogenetic data have prompted substantial revision of the traditional morphology-based genera and species, and aligning naming with phylogeny while preserving clinical usability remains an active discussion.

Seminal works

• dehoog-2016

Frequently asked questions

Is 'ringworm' caused by a worm?

No. Ringworm (tinea) is caused by dermatophyte fungi that infect keratinised tissue; the name refers to the ring-shaped skin lesion, not to any worm.

Why are dermatophyte infections named 'tinea' with different words?

The second word denotes the affected body site — for example tinea pedis for the feet, tinea capitis for the scalp, and tinea unguium for the nails.