Woolly hair nevus.

Woolly hair nevus is a rare, nongenetically determined condition in which unruly and tightly curled hair is localized on one or several areas of the scalp. We report the first case of woolly hair nevus with onset during adolescence. Marked improvement was evident 5 years after onset. Light microscopic examination of a biopsy specimen from the scalp showed a curved hair follicle. Scanning electron microscopic examination revealed slight fluting and marked flattening of the hair shafts. A discussion of these results and a comparison with those of the previously reported cases suggest that woolly hair nevus correlates with a variety of structural changes in the hair.