No other creature possesses true hair, and at least some hair is found on all mammals at some time during their lives. Hairs grow out of pits in the skin called follicles . The base of the hair, sunk in the skin, is called the root , and the part that emerges to the exterior is the shaft .
Follicles often lie next to a skin gland called a sebaceous gland .
These glands secrete an oily substance, which lubricates the hair and conditions it. Next to the follicle may be a small, involuntary arrector pili muscle . Hairs normally lie nearly parallel to the skin or at an acute angle to it. The shaft of a hair is made up primarily of a protein called keratin and consists of three distinct and easily recognizable parts. The outer layer is made up of dead, transparent cells called cuticular scales .