The dermatophytes, or ringworm fungi, include a group of fungi that have the ability to infect and survive only on dead keratin, the top layer, of skin, hair, and nails. The dermatophytes are ubiquitous in the environment and tinea infections are among the most common dermatologic disorders in the world. Dermatophytes are classified into three genera: Microsporum, Trichophyton, and Epidermophyton. The prevalent species of dermatophytes change with time and geographic location. The organisms may invade both the stratum corneum and the terminal hair shaft. Transfer of the organism may occur through the shedding of scales, autoinoculation, or transfer of spores. Microsporum canis is a frequent cause of tinea infections in children and is transferred from affected cats, dogs, horses, or cattle. Clinically, infections caused by dermatophytes are classified by the affected body region.

The history and physical exam will often establish the diagnosis of a dermatophyte infection. The use of laboratory resources, such as direct visualization of branching hyphae under a microscope, culture, or Wood’s light examination, increases diagnostic accuracy.