What determines the level of curl or wave in hair?

The level of curl or wave in hair is primarily determined by the shape of the hair follicle. Hair follicles can vary in shape, with round follicles producing straight hair, oval or elliptical follicles creating wavy hair, and flat follicles resulting in curly hair. The structure of the follicle influences how the hair emerges from the scalp and its subsequent characteristics.

In contrast, hair shaft thickness, while it can affect the perception of hair texture, does not directly determine the curl pattern. Hair density refers to the number of hair strands per area on the scalp, which affects fullness but not the pattern of curl or wave. Scalp condition impacts overall hair health but does not influence the inherent pattern of curl or wave that is established by the follicle shape.