(also called trichosporosis), a fungal disease of the hair caused by many varieties of the genus Trichosporon, one of the keratomycoses. In piedra, the hair shafts bear numerous barely perceptible spindle-shaped whitish to dark brown nodules with a distinctive pungent odor; the nodules consist of spores of the fungus. The hairs remain intact and there is no skin inflammation.

The American variety of piedra (black piedra) affects mainly women and infests only the scalp. The European form (white piedra) infests the beard and moustache. Piedra is not highly contagious; infection may occur through using a towel, hat, or comb used by an infected person. The infection becomes worse if the hair is washed with flaxseed extract or if the oil of repeinik roots (seeREPEINIK) is applied to the hair, since both substances supply nutrients to the causative agent.

Piedra is treated by shaving the affected areas, washing them with hot water and soap, and applying a 0.1–0.2 percent solution of mercury bichloride. Observance of the rules of personal hygiene is the best means of preventing the disease.