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Curly, straight, or somewhere in between—what determines your hair texture? It’s not all in your genes, but they do play a role. And even if you have curly hair, you could have DNA for straight hair (and vice versa). An AncestryDNA® test can tell you more about your natural hair type.

Hair Type and Hair Texture

More About Hair Type and Hair Texture.

If you were to put all the different hair textures into a hair type chart, you would see four main types: straight, wavy, curly, and tightly curled. 

Type 1 is straight hair that doesn't curl. Type 2 is wavy hair that is in between straight and curly. Type 3 is curly hair that looks like the letters "S" or "Z." Type 4 is hair that is coiled very tightly. 

You can break down the hair types and texture even more based on your hair's curl pattern, density, porosity, width, and length. For example, if you have one of the curly hair types, it can be type 3a (loose curls) or type 3b (tight curls like a spiral).

Genetics of Hair Type

Research shows that your hair's wave or curl is passed down in your genes. But hair curl is what's called an “additive" trait, which means that the amount of curl you have depends on how many curly hair gene variations you inherit. 

So, while curly-haired parents tend to have curly-haired kids, there's no guarantee it will happen.

Because many different genes are involved, even a curly-haired parent can have—and pass along—straight-hair gene variations. That's why in the same family, hair can be stick-straight, curly as a spring, or anything in between.

Genes can also interact with each other to determine your hair texture.

The Science Behind Hair Type

Genes aren't the only thing that affects your hair type. Your environment can have a big impact on your hair. Humidity can make your hair frizzy or curly, while cold winter air can make hair dry and static-prone. 

As you get older, your hair changes and becomes thinner and finer. Aging also makes your hair drier because the oil glands in your scalp start to shrink. 

How you treat and style your hair can change its texture. Bleaching, straightening, and coloring your hair can make it more dry and brittle. Relaxing your hair with chemicals can get rid of waves and curls. Perms can do the opposite and give you curls.

Interesting Facts About Hair Types and Texture

Straight hair may have become more common during the Ice Age, about 65,000 years ago. Because straight hair lays against the skin, it may have provided more protection from the cold. Straight hair also tends to be oilier, which protects it better during the cold.

Uncombable hair syndrome is a rare genetic disorder caused by mutations in the hair’s genes. It makes the hair very dry, frizzy, and hard to brush. The hair also grows outward from the scalp, so it sticks out in different directions. 

It’s not very common but hair can naturally become curly or straight later in life. Scientists don’t know exactly why this happens.

Curious about the connection between your DNA and your hair type? An AncestryDNA test can tell you more.

References

“Ask a Geneticist: Other Traits.” Stanford at the Tech Museum. August 27, 2004. http://genetics.thetech.org/ask/ask45.

Chang, Shie Hong et al. “Enhanced Edar Signalling Has Pleiotropic Effects on Craniofacial and Cutaneous Glands.” PLoS ONE 4, no. 10 (2009). doi:10.1371/journal.pone.0007591.

Engber, Daniel. “What Makes Hair Curly?” Popular Science. December 3, 2012. http://www.popsci.com/science/article/2012-11/fyi-what-maks-hair-curly.

“Genes and Hair Curl.” GB HealthWatch. Accessed July 13, 2016. http://www.gbhealthwatch.com/Trait-Hair-Curl.php.

Loussouarn, Geneviève et al. “Worldwide Diversity of Hair Curliness: A New Method of Assessment.” International Journal of Dermatology 46, no. S1 (2007): 2–6. doi:10.1111/j.1365-4632.2007.03453.x.

Thibaut, Sebastien et al. “Human Hair Keratin Network and Curvature.” International Journal of Dermatology 46, no. S1 (2007): 7–10. doi:10.1111/j.1365-4632.2007.03454.x.

Tirado-Lee, Leidamarie. “The Science of Curls.” Helix Magazine. May 20, 2014. https://helix.northwestern.edu/blog/2014/05/science-curls.