Dermatology

Fungal skin infections

Dermatophyte fungi digest keratin in the stratum corneum and spread outward as they consume it, producing a scaly lesion with an actively advancing, inflamed edge and a clearing centre, the ring that gives ringworm its name.

Definition

Fungal skin infections (dermatophytoses, or tinea) are superficial infections of keratinised tissue (skin, hair and nails) by dermatophyte fungi, and also include candidal and pityriasis (Malassezia) infections. They are named by body site, such as tinea corporis, cruris, pedis and capitis.

First principles

Dermatophytes live on keratin, not living tissue

Dermatophyte fungi such as Trichophyton and Microsporum use keratinised tissue in the stratum corneum, hair and nails. In an immunocompetent host, typical dermatophytosis remains superficial, but scalp and nail involvement require systemic treatment because topical medicines do not reliably reach the infected hair or nail structures.

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