superficial skin lesions caused by a highly specialized group of fungi called dermatophytes that live and multiply on the surface of the skin and feed on keratin, the horny protein constituting the major part of the outermost layer of the skin and of the hair and nails. The fungi produce responses in the skin that vary from slight scaling to blistering and marked disruption of the keratin layer. The lesions are usually round or ring shaped and can be either dry and scaly or moist and covered with vesicles (blisters), depending on the body area and the type of fungus involved.

Ringworm is also referred to as tinea, both names referring to the round shape of most of the lesions, similar to the larva of the clothes moth, genus Tinea. In specifying the condition, tinea is usually followed by a modifying term indicating the body area or characteristics of the lesions. Thus, ringworm of the scalp, beard, and nails is also referred to as tinea capitis, tinea barbae or tinea sycosis, and tinea unguium (also called onychomycosis), respectively; ringworm of the body, groin, hands, and feet, as tinea corporis, tinea cruris (also called jock itch), tinea manuum, and tinea pedis (athlete's foot), respectively. Tinea pedis is commonly referred to as athlete's foot, which may be of either the dry or inflammatory type. In the latter type, the infection may lie dormant much of the time and undergo occasional acute exacerbations, with the development of vesicles (blisters) affecting chiefly the skin folds between the toes. The dry type is a chronic process marked by slight redness of the skin and dry scaling that may involve the sole and sides of the foot as well as the toenails, which become thick and brittle.

Varieties of ringworm characterized by specific skin lesions include: Oriental ringworm, Tokelau ringworm, or tinea imbricata (Latin: “overlapping like tiles”), so called because it occurs chiefly in tropical climates and consists of concentric rings of overlapping scales; crusted, or honeycomb, ringworm, also called favus, a ringworm of the scalp, characterized by the formation of yellow, cup-shaped crusts that enlarge to form honeycomb-like masses; and black dot ringworm, also a ringworm of the scalp, deriving its distinctive appearance and name from the breaking of the hairs at the scalp surface. Except for ringworm of the scalp, which tends to be highly contagious, the contraction of ringworm depends to a large extent on individual susceptibility and predisposing factors, such as excessive perspiration.

Diagnosis of ringworm is made by observation and by microscopic examination. Treatment with topical or oral antifungal agents may be effective. Limited exposure to ultraviolet radiation may also be helpful.