Medical Definition of Hair follicle

Hair 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.

Skin illustration - Hair follicle

"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.

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Last Editorial Review: 5/13/2016

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