This is also a disease chiefly of the scalp, but the same fungus attacks the beard and the parts of the body devoid of hair. The disease is therefore divisible into three forms, Tinea tonsurans proper. Tinea sycosis, and Tinea marginata.

The fungus, called the Trichophyton tonsurans, is chiefly in the form of spores which infiltrate the hair and its sheath, as well as, to a less extent, the epidermis around. The mycelium is only represented by short threads. The hair shaft is greatly penetrated by the spores, which break it up.