What makes hair curly or straight?

You inherit from your parents genes which help determine whether your hair will be straight, curly, wavy, frizzy, thick or thin. But what actually makes your hair wave, or frizz or lie there bone straight is the shape of the hair itself. If you were able to cut a hair in half and look at it sideways you would notice that curly hair is shaped like rectangle, wavy hair like oval and straight hair like a circle. And that shapes determines whether your hair hangs down straight or spirals in the circle or waves in a curve.