Some people's hair changes significantly throughout their lives. This happens naturally, without artificial methods like perms. Pregnancy, or going through puberty, can change a person's hair from straight to curly or the other way around.
The reasons for these kinds of changes aren't clear, but scientists think it's related to hormones, genetics, and a person's body chemistry.
The Anatomy of Hair
But how curly or straight hair is depends on the shape of the follicle. That's the structure that produces hair.
Round follicles produce straight hair. Curly hair comes from oval-shaped follicles that have a twist at the bottom. When hair moves through round follicles, it gets evenly coated with a protein called keratin.
Keratin is what gives human hair structure. Hair that grows through oval follicles tends to have more keratin on one side than the other. As a result, it curls.
The process is similar to taking a pair of scissors and running it along plastic gift wrapping ribbon. One side of the ribbon gets stretched out more than the other, so it curls in on itself.
Artificial curling methods like perms don't change the shape of hair follicles, which is why perms grow out. Permanent wave solutions disrupt the chemical bonds in your hair, then forge new ones when the hairstylist puts your hair in curlers.
Sources and Further Reading
- Ray, C. C. Enough to Curl Your Hair, New York Times, May 13, 2013.
- Thibaut, S., et al. (2007). Human hair keratin network and curvature. International Journal of Dermatology, 46, 7-10.