Definition of Hair follicleHair follicle: A sac from which a hair grows and into which the sebaceous (oil) glands open. The follicle is lined by cells derived from the epidermal (outside) layer of the skin. Each follicle normally goes through a five-year cycle of growth and rest, with about 90% of the follicles growing hair at any one time, averaging about six inches (15 cm) of growth per year. Derived from the Latin word follis, for bag. ![]() "The human hair follicle is a dynamic structure that generates hair through a complex and exquisitely regulated cycle of growth and remodelling governed by numerous genes," Siobhán A. Jordan has noted in Molecular Medicine Today. Last Editorial Review: 4/27/2011 5:27:15 PM
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