Why No Single “Curly Hair Gene” Tells the Whole Story
If you have ever wondered why your hair looks different from your sibling’s hair, or why your child’s hair changed after puberty, you have stumbled onto one of the most fascinating facts about human hair: hair texture is not controlled by a single gene.
There is no “curl button” and no “straight button” hidden in your DNA. Instead, hair shape is influenced by many genes working together. Some of these genes affect the shape of your hair follicle. Some affect the thickness of each strand. Some affect the angle at which hair grows from your scalp. And some affect the microscopic structure of the hair fiber itself.
This polygenic complexity is why human hair forms a spectrum, not a set of neat boxes. And it is why the same family — even identical twins — can have noticeably different hair.
This article explores the major genes that scientists have identified as playing a role in human hair texture, how they work, and what their distribution across different populations tells us about human history.
EDAR: The Gene for Thick, Straight Hair in East Asians
One of the most powerful genes affecting human hair texture is called EDAR (Ectodysplasin A Receptor). This gene is involved in the development of several ectodermal structures during embryonic development, including hair follicles, teeth, and sweat glands .
A specific variant of this gene, known as EDARV370A (often shortened to EDAR370A), is extremely common in East Asian and Native American populations. In these populations, the variant is found in nearly 95% of people. In contrast, it is very rare in people of African or European ancestry .
What does this genetic variant do? In simple terms, it makes hair thicker and straighter.
Researchers have confirmed this by creating genetically modified mice that carry the human EDAR370A variant. These mice grew thicker hairs in their fur than normal mice, matching the effect seen in humans .
But here is where the story gets even more interesting. The EDAR370A variant did more than just thicken hair. The same mice also developed more sweat glands, denser mammary glands, and smaller fat pads around those mammary glands . When researchers checked human volunteers in China, they found the same pattern: people carrying the EDAR370A variant had noticeably more sweat glands on their fingers .
So what was the actual evolutionary advantage? Did the thicker, straighter hair help with cold protection in northern climates? Or did the extra sweat glands help with cooling in humid environments? Or did the changes in mammary glands improve infant survival? The answer is not yet clear, and it is possible that multiple advantages worked together .
What scientists do know is when and where this variant appeared. By analyzing DNA from people around the world and running computer simulations of how the variant spread, researchers estimate that EDAR370A arose in central China approximately 30,000 years ago . From there, it spread rapidly through East Asian and Native American populations — a strong sign that it offered a survival advantage to the people who carried it.
TCHH: The Gene That Makes Hair Curly in Europeans
While EDAR is the major player in East Asian hair texture, a different gene takes center stage in people of European ancestry. That gene is called TCHH (Trichohyalin).
Trichohyalin is a protein produced in the inner root sheath of the hair follicle — the rigid “mold” that shapes the developing hair fiber before it emerges from the skin . If you think of the inner root sheath as a cookie cutter, trichohyalin is one of the main ingredients that gives that cookie cutter its structure.
A large genome-wide association study published in 2009 analyzed hair shape in over 5,000 people of European descent. The researchers found that common variants in the TCHH gene were strongly associated with hair curliness — specifically, with straighter hair .
| Finding | Detail |
|---|---|
| Gene identified | TCHH (Trichohyalin) |
| Variance explained | ~6% of hair shape differences in Europeans |
| Most significant SNP | rs11803731 (p = 1.5 × 10⁻³¹) |
| Highest frequency | Northern Europeans |
The TCHH variant associated with straighter hair is most common in Northern Europeans and reaches its lowest frequency in Southern European populations like Italians and Spaniards . This geographic pattern parallels the distribution of the EDAR variant in Asia — in both cases, a variant that promotes straighter hair is common where it is cold, and rarer where it is warm.
Unlike EDAR, however, the selective pressure on TCHH is less clear. The variant does not show the same unmistakable signature of recent positive selection that EDAR does . It may have spread through a combination of natural selection (perhaps for cold adaptation) and genetic drift.
PRSS53: A Player in Multiple Populations
Another gene involved in hair shape is PRSS53, which encodes a protein called serine protease 53. This protein is involved in the processing of other proteins in the hair follicle, particularly those that help form the inner root sheath .
Variants in PRSS53 have been associated with hair shape in multiple populations, including East Asians, South Asians, and Africans . This suggests that PRSS53 plays a fundamental role in hair biology that cuts across population boundaries — unlike EDAR and TCHH, which have stronger effects in specific geographic groups.
What makes PRSS53 particularly interesting is that two separate variants in this gene — called Q30R and G34S — show evidence of having been targets of natural selection in East Asian and South Asian populations, respectively . Both variants involve changes in just one amino acid in the protein sequence, yet they appear to have offered enough of an advantage to spread through entire populations.
The overlap between PRSS53 and EDAR is also notable. Both genes affect hair shape, both are under selection in East Asian populations, and both are active in the same region of the hair follicle . This suggests that hair shape has been shaped by natural selection not through a single genetic change, but through multiple independent changes that all pushed in the same direction.
KRT71, KRT74, and the Inner Root Sheath
The keratin genes KRT71 and KRT74 deserve special attention because they are expressed specifically in the inner root sheath (IRS) of the hair follicle . If you recall from Article 3, the IRS acts as a rigid mold that shapes the hair fiber as it grows. If the IRS is abnormal, the hair fiber will be abnormal.
In humans, mutations in KRT71 and KRT74 can cause a rare condition called woolly hair — hair that is fine, tightly curled, and grows more slowly than normal . These mutations are rare and cause obvious changes in hair texture.
But what about normal variation in hair shape? It is likely that more subtle differences in the activity of KRT71 and KRT74 — caused by common genetic variants, not rare mutations — contribute to the normal range of hair curliness in the general population. Researchers are still working to identify exactly which variants matter and how much they contribute .
Other Genes: WNT10A, FRAS1, OFCC1, and Beyond
The list of genes associated with hair shape continues to grow. Here are some of the other confirmed players:
| Gene | Association | Notes |
|---|---|---|
| WNT10A | Hair shape + hair disorders | Variants near this gene are associated with straight hair; mutations cause syndromes with abnormal hair |
| FRAS1 | Straight hair in Europeans | First identified in a genome-wide association study, function in hair is still being studied |
| OFCC1 | Hair shape | Confirmed in multiple studies across European and other populations |
| FGFR2 | Hair thickness in East Asians | Works alongside EDAR to produce thick, straight hair |
| GATA3 | Hair shape | A transcription factor that regulates the expression of other genes in the hair follicle |
In total, genome-wide association studies have identified at least 12 genetic loci associated with human scalp hair shape . Some of these contain single genes. Others contain multiple genes working in the same pathway.
This number continues to grow as researchers analyze larger and more diverse datasets. A 2015 study of nearly 30,000 people identified 12 loci and also confirmed the roles of EDAR, PRSS53, and OFCC1 . A 2025 study in Han Chinese identified new variants associated with hair density and the number of hairs per follicular unit . Each new study adds pieces to the puzzle.
The Polygenic Reality: Why It Matters
Here is the most important thing to understand: your hair texture is the result of all of these genes working together.
You might inherit the EDAR variant for thick hair from one parent and the TCHH variant for straight hair from the other. Or you might inherit the ancestral version of all these genes, which tends to produce curlier hair (since tightly curled hair appears to be the ancestral state for modern humans).
This is why two siblings can have noticeably different hair. Each child inherits a different combination of genetic variants from their parents. And because so many genes contribute, the possible combinations are nearly endless.
It is also why hair texture can change with age, hormones, or health. Many of these genes are sensitive to signals from your body — including hormones like androgens and estrogens. This is why a child’s hair can change at puberty, and why hair texture sometimes shifts during pregnancy or menopause . The genes are still there, but their activity levels have changed.
From Genes to Follicles to Curls
The ultimate goal of all this genetic research is to understand the molecular mechanisms that determine hair shape. How does a change in a single amino acid in the EDAR protein lead to thicker, straighter hair? How do variants in TCHH affect the inner root sheath’s ability to mold the hair fiber?
Researchers are approaching these questions from multiple angles:
- Mouse models allow scientists to insert human genetic variants and observe their effects in a living animal
- Cell line experiments allow researchers to study how genetic variants affect protein function at the molecular level
- Hair follicle culture allows scientists to grow human hair follicles outside the body and study how they respond to different factors
- Transcriptomics (measuring which genes are turned on or off) allows researchers to compare straight and curly hair follicles at the molecular level
One recent study compared gene expression in very curly versus straight hair follicles and found differences in the transcription of genes involved in the inner root sheath, including CGA, FMO1, GSTM4, and FKBP2 . These genes had not previously been linked to hair shape, suggesting there is still much to discover.
A Note on Race and Genetics
It is important to be careful here. When scientists talk about EDAR being common in East Asians or TCHH variants being common in Europeans, they are describing patterns of genetic variation across geographic populations. These are real biological facts.
But these patterns do not mean that all East Asians have thick, straight hair (they do not). They do not mean that all Europeans have wavy or curly hair (many have straight hair). And they do not mean that people of African descent lack genetic variation in hair texture (Africa has the greatest genetic diversity on the planet, including in hair-related genes).
The genes described in this article are the ones that have been discovered so far. The vast majority of studies have been conducted on people of European or East Asian ancestry, meaning many relevant genes may have been missed simply because researchers have not looked in diverse enough populations .
Your hair is the product of your unique combination of genes — not your race, not your ancestry, not your family tree. Those things influence which genetic variants you are likely to have, but they do not determine your hair. Your specific mix of variants does.
What This Means for Understanding Your Hair
The next time someone asks you why your hair is the way it is, the honest answer is complex.
It is because of the shape of your follicles. It is because of the asymmetry of your inner root sheath. It is because of the specific combination of genetic variants you inherited in EDAR, TCHH, PRSS53, KRT71, KRT74, WNT10A, FRAS1, and a dozen other genes scientists are still discovering.
Each of those genetic variants has its own story — a story of where it arose, how it spread, and what advantage it may have offered to the people who carried it.
Some of those stories are about climate: thicker hair for cold protection, curlier hair for heat protection, extra sweat glands for humid environments.
Some of those stories are about chance: a random mutation that happened to spread because a small group of people carried it into a new land.
And some of those stories are about attraction: features that people found beautiful or meaningful, passed down through generations not because they helped survival, but because they helped belonging.
All of those stories are written in your DNA. And they all come together, in the follicles beneath your scalp, to produce the hair on your head.
Every curl, every wave, every straight strand is the product of thousands of genetic variants, thousands of generations, and thousands of miles of human migration.
That is not simple. That is not a single gene. That is the beautiful complexity of being human.
References
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Disclaimer: This article was researched and drafted with the assistance of AI. All sources are real and verifiable. Readers are encouraged to check the references themselves and draw their own conclusions.
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