Fungi are eukaryotic (contain a true nucleus) organisms that lack chlorophyll and rely on preformed organic matter as their energy source. Fungi may be grouped into two broad categories-yeasts and molds-based on their physical characteristics (single cells or hyphae) and mode of reproduction (budding or spore formation). Many species are dimorphic and may exist as yeast and as molds depending on the temperature or other characteristics of the physical environment. In general, fungi grow in damp, dark environments. The specific type of fungi present in a particular area depends on environmental conditions and available substrates. Of more than 100,000 fungal species, only several hundred cause infection and disease in humans. Fungi are found ubiquitously in the environment; however, despite this constant exposure, serious fungal diseases are rarely found in immunocompetent individuals.
Fungal infections, called mycoses (myco Latin for fungus), may be superficial, deep, or systemic, and may cause very mild to life-threatening disease.
The most common types of fungal infections are superficial skin infections caused by a variety of fungal species known as dermatophytes. While most fungal infections are not spread from person to person, superficial mycoses often are. The clinical conditions, tinea pedis, tinea manis, tinea corporis, and tinea capitis, affect the feet (athlete's foot), hands, body, and head, respectively. These infections are most often an itchy nuisance which can usually be easily controlled with topical medications. Pytiriasis versicolor is a fungal skin infection most often found around puberty and causes hyper- or hypo-pigmentation of the skin. Onychomycosis is a fungal infection of the finger or toe nails which can be chronic and difficult to treat. Piedra is a fungal colonization of the hair shaft in which the color and steadfastness of the fungal nodules depends on the species of fungus. A species of yeast called...