Hair begins in the dermis layer of the skin and pushes outward. It is made up primarily of protein keratin. Unlike other portions of the body, the hair is only alive at the root, where the sebaceous gland produces oil to lubricate the hair.

Strands of hair are made up of three parts. Cuticle is the outermost layer, and varies in thickness based on genetics. Underneath the cuticle is the cortex, which determines both the color and shape of the hair. The cortex is made up of mostly melanin, the same thing that determines skin pigment.