Direct inoculation of the spores through breaks in the skin can lead to germination and subsequent invasion of the superficial cutaneous layers. Dermatophyte infections occur more frequently in certain ethnic groups and in people with impaired cell-mediated immunity. Many of the anthropophilic dermatophyte infections are more likely to occur in persons of certain age groups and are more common in males or in females. Infection of the scalp, for example, is primarily a disease of children. Involvement of the feet and groin is most common in adolescents and young adults, especially men, but is unusual in children.
Nail infection is more frequent in both sexes with advancing age.
The reasons for these differences are unknown. The anthropophilic dermatophytes also have unique geographic distribution patterns. The most common cause of scalp infection in the United States, for example, is T. tonsurans, but in Southeast Asia and the Middle East, T. violaceum is the most common cause. These differences may relate to climatic or racial factors. The various forms of dermatophytosis, also called ringworm, are named according to the site involved.