The term wooly hair refers to an abnormal variant of hair that is fine, with tightly coiled curls, and often hypopigmented. Optical microscopy may reveal the presence of tight spirals and a clear diameter reduction as compared with normal hair. Electron microscopy may show flat, oval hair shafts with reduced transversal diameter. The phenotype is Human Phenotype Ontology entry HP_0002224 (Woolly hair). Also known as: Kinked hair, Wooly hair.