Human hair typically grows on the face, scalp and body, with a few exceptions such as palms, lips and bottoms of the feet. Over the centuries, hair has gone from serving a purely functional role, such as protection from extreme temperatures and microbes, to acting as a major indicator of style and personal aesthetic, especially the hair on your head. Hair, which is made of a protein known as keratin, usually consists of three layers: the medulla is the innermost layer (not always present); the cortex is in the middle; and the cuticle is on the outside. The hair strands are contained in stocking-like cavities known as follicles. The only living part of the hair is at the root, which lies at the base of the follicles. A man's beard typically contains between 7,000 and 15,000 hair follicles. Human hair grows at an average of one-quarter inch per month.