All hair, whether straight or curly is made up of of the same components. However, the shape of hair follicle, which is largely a result of genetics, determines whether hair is straight, wavy or curly. The straighter the hair, the rounder the shape of the follicle. Curly hair has elliptical shaped follicles that bend and turn. The more elliptical the shape of the hair shaft, the curlier the hair. Most follicles contain sebaceous glands, which are responsible for releasing an oily substance called sebum that lubricates the hair.