Structure and layers of the skin. The hair follicle is a skin appendage located deep in the dermis of the skin. Its function is to produce hair and enclose the hair shaft. A hair follicle consists of two main layers, an inner (epithelial) root sheath and an outer (fibrous) root sheath.

Follicles that produce terminal hairs extend into the deep dermis and, sometimes, even the subcutis. Meanwhile, follicles producing vellus hairs extend only to the upper reticular dermis. Three essential segments of hair follicles are found on the head: the infundibulum, isthmus, and lower follicle.

Basic hair structure explained. Learn how all parts of the hair follicle and layers of the hair shaft function together with diagrams.

Histology of hair follicles (longitudinal sections), sebaceous glands, eccrine glands, and arrector pili muscles in thin skin.

Strands of hair originate in an epidermal penetration of the dermis called the hair follicle. The hair shaft is the part of the hair not anchored to the follicle, and much of this is exposed at the skin’s surface. The rest of the hair, which is anchored in the follicle, lies below the surface of the skin and is referred to as the hair root.