Ringworm is a a term loosely used to designate different red, scaly, itchy, sometimes blistered or oozing skin troubles. Medically ringworm is always caused by some fungus of the group known as dermatophytes, so called because they are vegetable parasites affecting dermal structures (skin, hair, nails). In typical cases the clinical appearance and course indicate the species of causal fungus. But the clinical findings are not pathognomonic; so that microscopic examinations and particularly fungous cultures are often essential for precise identification of the causal species. Identification is sometimes of great importance, for the diseases caused by different species of dermatophytes can require entirely different methods of treatment and epidemiologic control. Thus the common Microsporum audouini infection almost exclusively affects the scalp hairs of children, is quite readily transmissible, usually heals spontaneously at puberty, but, as therapy, generally requires temporary depilation (such as by X-rays).
Other common dermatoses caused by species of dermatophytes include eruptions of the feet (also known as "athlete's foot"), of the groins and other large skin folds, of the nails, or of the beard or scalp hairs. Sources of infection are lower animals (livestock, cats, and dogs- "zoophilic fungi"), persons ("anthropophilic fungi"), and, much less frequently, contaminated objects. Human infections by zoophilic fungi generally have less contagiousness for other persons, more inflammation, and stronger tendencies to spontaneous healing; while infections by anthropophilic fungi usually exhibit greater contagiousness, less inflammation, less tendency to spontaneous cure. Scalp hair infections by zoophilic Microsporum lanosum are thus contrasted with the above-described infection by anthropophilic Microsporum audouini.
The clinical pictures produced and the treatments required by different forms of ringworm are so diverse that inclusive descriptions are inevitably misleading. Moreover, the term "ringworm" is itself misleading, for the majority of fungous skin infections do not produce rings, while many nonfungous skin diseases can produce annular lesions. Ringworm of the skin and its appendages is generally without systemic ill effects, but is of such high incidence that it causes an enormous total of discomfort and disability, especially among those exposed to skin wetting, high temperatures, and humidity.