Black piedra, also known as trichosporosis or nodular trichomycosis, is a superficial mycosis of the hair shaft caused by Piedraia hortae, a pigmented fungus. Patients present with darkly pigmented nodular concretions on the hair of the beard, scalp, brows, or lashes; it may occur less commonly in the axillae or pubic region. The nodules are distributed in an irregular array along the hair shaft. Black piedra is chronic and asymptomatic.

Most cases occur primarily in tropical regions with heavy rainfall, especially in South America and Asia, among young men and women and children. The most critical predisposing factors to infection are humidity and poor personal hygiene.