Outer Root Sheath

The outer root sheath (ORS) is an extension of the epidermal basal layer which envelopes the entire hair follicle (HF). In addition, the ORS contains a number of functional compartments: the bulge, which serves as a reservoir for hair stem cells, and the sebaceous gland, responsible for hair lubrication. The upper region of the ORS is a site for attachment of ancestor pili, which are smooth muscles that enable the hair to remain in a vertical position.