Curly, straight, or somewhere in between—what determines your natural 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^® + Traits test can tell you more about your natural hair type.

The Range of Hair Types and Hair Textures

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 very tightly coiled like a corkscrew.

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 variants 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 strands can be stick-straight, form loose ringlets, be as curly as a spring, or anything in between.

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

Ancestry scientists can predict how curly your hair is by looking at over 2000 DNA markers associated with the trait.

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. High humidity can make your hair frizzy or curly, while low-humidity and cold air can make hair dry and static-prone.

The hormonal changes that occur during pregnancy or menopause can also impact your hair’s texture. Pregnant women may notice that their hair seems thicker, while menopausal women may notice that their hair texture has become coarser.

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.

Certain medical treatments like chemotherapy may also change your hair texture. New, post-treatment hair growth may be curlier or straighter than usual because of changes that have impacted the hair follicles.

How you treat and style your hair can also 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 genes that control hair growth. 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.

Curious about the connection between your DNA and your type of hair? An AncestryDNA^® + Traits 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, Stephanie Jobling, et al. "Enhanced Edar Signalling Has Pleiotropic Effects on Craniofacial and Cutaneous Glands." PLoS ONE. October 2009. https://journals.plos.org/plosone/article?id=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 August 4, 2023. http://www.gbhealthwatch.com/Trait-Hair-Curl.php.

Herman-Axel, Paige. "Style Solutions: When Your Hair Texture Changes." Radiance by WebMD. Accessed August 14, 2023. https://www.webmd.com/beauty/features/texture-changes.

Loussouarn, Geneviève, et al. "Worldwide Diversity of Hair Curliness: A New Method of Assessment." International Journal of Dermatology. October 2007. doi:10.1111/j.1365-4632.2007.03453.x.

"Quick Dose: Why Does Your Hair Grow Back Differently After Chemotherapy?" Northwestern Medicine. Accessed August 14, 2023. https://www.nm.org/healthbeat/healthy-tips/Quick-Dose-Why-Does-Your-Hair-Grow-Back-Differently-After-Chemotherapy

Thibaut, Sebastien, et al. "Human Hair Keratin Network and Curvature." International Journal of Dermatology. October 2007. doi:10.1111/j.1365-4632.2007.03454.x.

Tirado-Lee, Leidamarie. "The Science of Curls." AskMags.com. Accessed August 4, 2023. https://askmags.com/the-science-of-curls/.