The vast majority of fungal infections of the skin, hair, and nails are caused by the dermatophytes, and yeasts including Candida species and Malassezia furfur. Because these entities can mimic nonfungal diseases, proper diagnosis is essential. Some fungi causing systemic infections may begin as cutaneous lesions. In most cases, potassium hydroxide (KOH) preparation, culture, and or biopsy can give a definitive diagnosis. Treatment may involve topical and/or systemic antifungal therapy.
THE DERMATOPHYTES
The dermatophytes are keratinophilic organisms that are found in specific ecological niches. Those found in the soil are referred to as geophilic organisms. Some primarily infect hair, skin, and nails of humans and are transmitted human to human (anthropophilic), and others are mainly found in fur, feathers, skin, and nails of animals (zoophilic). When transmitted to humans, zoophilic and geophilic organisms tend to be much more inflammatory than anthropophilic organisms. Factors precluding dermatophycosis include inoculum size, host immune status, the particular organism, a suitable environment, fungal growth rate exceeding epidermal turnover, and in certain instances the host genetics.
The term tinea refers to dermatophycosis or a dermatophyte infection due to one of the following genera: Epidermophyton, Trichophyton, or Microsporum. Dermatophyte infections are described by their location on the body: tinea capitis (scalp), tinea corporis (glabrous skin), tinea faciei (face), tinea cruris (groin), tinea manuum (hand), tinea pedis (feet), tinea barbae (beard), and tinea unguium (nails).