Woolly hair nevus (alternatively spelled wooly hair nevus) is a localized noninherited alteration of scalp hair often presenting at birth or in the first several years of life. It is a rare abnormality characterized by extreme kinkiness of hair. Classically, the hair in woolly hair nevus is curly or coiled, smaller in diameter, and lighter in color.

Type 1 woolly hair nevus is an isolated finding. Type 2 woolly hair nevus, which is seen in 50% of cases, is a mosaic RASopathy associated with linear verrucous epidermal nevus. Type 3 wooly hair nevus is acquired in young adults and is also known as acquired progressive kinking of scalp hair.

Woolly hair nevi can also be associated with ocular findings including heterochromia iridis and persistent pupillary membrane. Auditory, dental (diastema, decayed lower canine teeth), skeletal (growth impairment, brachyphalangy), and renal anomalies have also been identified.

A few cases of woolly hair nevus in patients with incontinentia pigmenti have been reported.