Hair is largely made up of a protein called keratin. Cells in the hair follicle regularly produce the keratin and other proteins that become incorporated into the hair shaft.
Coloration comes from melanocytes which produce the brown pigment melanin.
More linking produces curlier hair. 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.