There are several types of fungal infections of the skin. Most cutaneous mycoses are caused by dermatophytes, a group of filamentous fungi that colonize and infect keratinized tissues, including the outermost layer of skin (i.e., stratum corneum), hair, and nails. Dermatophytes are commonly found in the environment and are spread from one person to another through direct skin contact or, more rarely, through contact with an infected animal or soil. Although there are a number of dermatophyte species, most dermatophyte infections are caused by fungi of the Trichophyton, Microsporum, and Epidermophyton genera.
Dermatophyte infections of the skin are also called tineas, or ringworm, due to the ring-like appearance of the skin lesions they typically produce. Some tineas have distinctive names descriptive of the affected body part. For instance, tinea corporis (i.e., ringworm) affects the arms, trunk, and legs; tinea capitis (i.e., scalp ringworm) affects the scalp and hair shafts; tinea cruris (i.e., jock itch) affects the groin area and inner thighs; and tinea pedis (i.e., athlete’s foot) affects the feet.
In addition to dermatophytes, cutaneous mycoses may also be caused by yeasts of the Candida genus. Candida is naturally present on the skin and mucous membranes. When the amount of Candida is low, it is harmless, but when it starts to overgrow, it can damage the skin and nearby tissues, resulting in a superficial skin infection. A weakened immune system is often the reason for Candida overgrowth. As a result, candidiasis typically affects individuals with immunosuppressive conditions (e.g., diabetes, HIV infection), who are more vulnerable to opportunistic infections.
More rarely, cutaneous mycoses can be due to infection by non-dermatophytic fungi, like an Aspergillus species. Aspergillus is a family of molds consisting of many different species, some of which can cause a condition known as aspergillosis. Cutaneous aspergillosis is a rare form of locally invasive disease that typically occurs when invasive aspergillosis spreads to the skin from somewhere else in the body, such as the lungs. Primary infection of the skin --such as after a surgery, trauma, or burn wound -- may also occur but is much less common.