In general, your hair type refers to how curly or straight it is, which is called your “curl pattern.” (If you have straight hair, your curl pattern is…straight. Bet you didn’t see that one coming.) Your curl pattern is determined by the shape of your hair shaft—curly hair is oval-shaped, straight hair is round, and coily hair is flat.

In straight hair, all the cells in the follicle act in a coordinated fashion, leading to even hair growth from the straight follicle. These hairs are round. However, in curly hair, the way that the cells divide and produce certain proteins is asymmetrical and correlates with the bends in the curved follicle.