The process can also be carried out chemically as happens with a permanent wave. So the main difference between naturally curly hair and straight hair is in the amount of disulfide linking in the hair shaft. The papilla, a net of nerves and capillaries that supplies the hair, extends into an indentation at the base of the root. Here newly dividing cells force older cells upward, where they die and harden into the hair shaft. The shaft has two layers, the colorless cuticle and the cortex, which contains pigment and the protein keratin.
Hair is lubricated by oil from sebaceous glands in the follicle.