Hair is primarily composed of keratin, a protein, which grows from the follicle. Keratins, and other proteins, are formulated in the cells of the hair follicle. All of the proteins become a part of the hair shaft and contain sulfur atoms. When two sulfur atoms pair up and bond, they form a disulfide bond. If the two sulfur atoms in the same protein are at a distance, and join to form the disulfide bond, the protein will bend. This is how your curls are created.