A fungal disease of the hair in which the hair shafts carry hard masses of black or white fungus. The black fungus, Piedraia hortai, is found mainly in the tropics and the white variety, Trichosporon cutaneum, in temperate regions.
Sheath-like nodular masses in the hair of the beard and mustache from growth of either Piedraia hortai, which causes black piedra, or Trichosporon beigelii, which causes white piedra. The masses surround the hairs, which become brittle; hairs may be penetrated by fungus and thus split.