What Determines Hair Curl and Texture

Straight, wavy, coiled, thick, fine - hair varies enormously between people, and it is tempting to imagine one gene sitting behind the difference. There is no single “curl gene.” Hair shape is polygenic, built from the combined nudges of many variants, and a couple of the best-known ones reveal how tangled the biology really is.

Hair shape is polygenic

The curliness and texture of your hair emerge from how the hair follicle is shaped and how the growing shaft bends as it forms. Many genes influence that process, each contributing a small amount, which is why hair does not fall into a few tidy categories but spreads across a smooth range. Two siblings can land in very different places because they inherited different combinations of the same shared variants.

Because the effect is spread across so many positions, no single letter in your DNA file decides whether your hair is straight or curly. Any one variant only tips the odds slightly. This is the same reason ancestry and appearance rarely map onto one gene.

The TCHH variant and straighter hair

One well-studied piece of the puzzle is a variant in the TCHH gene, rs11803731. In people of European ancestry, one version of this variant is associated with straighter hair. TCHH encodes a protein involved in the internal structure of the hair shaft, so it is plausible that changes here affect how the shaft holds its form.

Notice the careful wording: associated with straighter hair, in Europeans. The link has been observed most clearly in that population, and it shifts the probability rather than guaranteeing an outcome. Someone can carry the straight-associated version and still have wavy hair, because all the other contributing genes are voting too.

EDAR: one variant, several visible effects

The most striking example is the EDAR variant rs3827760. A particular version is common in East Asian and Indigenous American populations, and it does something remarkable - it influences several unrelated-looking traits at once:

• Thicker, straighter hair
• Shovel-shaped incisors (a scooped appearance on the back of the front teeth)
• More sweat glands

One variant, several visible effects. This is called pleiotropy, where a single genetic change ripples into multiple traits because the gene is active in more than one developmental process. EDAR is involved in the early formation of skin, hair, teeth, and glands, so a change to it leaves fingerprints across all of them.

It is a useful reminder that a variant is not labeled “for hair.” Genes do jobs, and those jobs can touch several parts of the body at once. If you have ever wondered why the genotype in a file rarely maps neatly to one trait, our piece on genotype versus phenotype unpacks exactly that gap.

Why there is no curl switch

Put the pieces together and the picture is clear. Hair texture is the sum of many small genetic contributions layered on top of factors like age, hormones, and even humidity on a given day. TCHH nudges toward straighter hair in some populations; EDAR reshapes hair while also touching teeth and sweat glands; and a long list of other variants each add their own small vote. No single one of them is in charge.

This is why looking up one marker cannot tell you your hairstyle, only add a little context to what you already see in the mirror. The same logic runs through other appearance traits, from eye color to freckling.

Exploring your own variants

If you are curious, markers like rs3827760 and rs11803731 often appear in consumer raw data, and you can look them up privately using on device DNA analysis that keeps your file in your browser rather than uploading it anywhere. Treat the results as one interesting thread in a much larger weave, not the final word on your hair.

This article is educational and is not medical advice.