Hi, I'm Craig. I have naturally long flowing hair, this balding is cosmetic. And this is Mental Floss Video. Today I'm going to answer clairebellxo's big question: What makes hair naturally straight or curly? Let's get started. Ah, sorry. Habit.

(Intro)

According to a study conducted in 2009, wavy and curly hair have a heritability of around 85 to 95%. Basically if a person has curly hair it's very likely that their child will have curly hair too. The environment plays a role as well, but a much smaller one. So if both your parents pass along a curly hair gene you'll probably have curly hair. And the same goes for straight hair. If both have it then so will you. If one passes down a curly hair gene and another passes down a straight hair gene then you'll likely have wavy hair.

But how do these genetics make hair appear a certain way? Well, they actually affect it at the follicle level. A hair follicle is a tiny organ below the skin that produces hair, and for hair to grow it has to be forced through a tube whose shape affects the hair. People with curly hair have asymmetrical follicles - my nickname in high school. Kids can be so cruel - which grow oval hair that curls. Your hair also tends to grow at a sharp angle. And people with straight hair have symmetrical follicles with round hair rather than oval.

And these genes actually vary from population to population. You may have observed that typically Asians are less likely to have curly hair than Africans, and Europeans fall somewhere in the middle. According to the Genetic Science Learning Center at the University of Utah, "Straight hair in Asians is mostly caused by variations in two genes - different genes from the ones that influence hair texture in Europeans. And different genetic variations make hair curly in African and European populations."

There are some people whose hair changes from curly to straight or the other way around though. Experts haven't figured out how this is possible. It probably means that the follicle itself has changed, or they got a hair straightener. Duh. Some believe that it happens thanks to a cell surface receptor known as the epidermal growth factor receptor, or EGFR, or EGFR. These can grow outside of the follicle and potentially change how hair grows.

Thanks for watching Mental Floss Video which is made with the help of these nice follicles. If you have a big question of your own that you'd like answered, leave it below in the comments. See you next week. Come on back hair. (Laughs).