Scientists have long wondered why some people have curly hair, while others do not, or why in some places on the body the hair curls, and in others it is straight. At the moment, there are two reasons that answer the question: why hair curls - this is the shape of the hair and the shape of the bulb.
If you look at the cross section of the hair under a microscope, you will notice that straight smooth hair is round in cross section, and curly hair is flattened. And the more hair is flattened, the stronger it curls. Interestingly, the shape of the hair can be a sign of race.
For example, the hair of the Indians is completely straight, since the shape of the hair is cylindrical, but the hair on the heads of people of the black race, on the contrary, curls strongly, because in cross-section they have the shape of an ellipse. Pubic hair is also subject to the same pattern - it curls because it is naturally flattened.
Interestingly, Asians usually have pubic hair that is almost straight and not as thick as that of Caucasians and Negroids.
Having examined hair follicles (bulbs) in laboratory conditions, French scientists noticed that in people with curly hair, the follicles have a curved shape, while in people with straight hair, they are even. This stems from the bulb itself, which directs hair growth.
An interesting fact, the shape of the hair follicles and the shape of the hair cut are transmitted from parents to children, but the reason why they are different in different people has not been established to date.