Most of the human body is covered by hair apart from one side of the fingers, the soles of the feet and palms of the hand. The hair shaft is the part of hair that emerges above the surface of the skin. The hair root is the part that extends deep into the dermis and even sometimes into the subcutaneous layer. The medulla, cortex and cuticle are the layers of concentric cells that form the hair shaft and root.

The roots of the hair cells are contained in deep pits, called follicles, in the skin, which reach down into the dermis. They are surrounded by a structure called a bulb which holds the papilla of the hair which provides nourishment for the growing hair through its many blood vessels and connective tissues. The sebaceous glands are connected to the hair follicle and secrete an oily substance known as sebum into the neck of the hair follicle. It coats the surface of the hair and prevents it from drying or becoming brittle.