5. The Genetics of Hair Color

How Hundreds of Genes Paint the Spectrum on Your Head

If you have ever wondered why your hair is a different shade from your sibling’s hair, or why your child’s hair changed color as they grew, you have stumbled onto one of the most fascinating facts about human genetics: hair color is not controlled by a single gene.

There is no “blonde button” or “brunette switch” hidden in your DNA. Instead, hair color is influenced by hundreds of genetic positions across the human genome . Some of these genes affect how much eumelanin (dark pigment) your melanocytes produce. Others affect how much pheomelanin (red-yellow pigment) they produce. Some control the shape and function of the melanosomes — the tiny packets that carry pigment into the growing hair shaft. And others regulate the activity of the first group.

This polygenic complexity is why human hair color forms a spectrum, not a set of neat boxes. It is why two brown-haired parents can have a blonde child. It is why red hair can skip generations. And it is why predicting a person’s hair color from their DNA — while possible — is still an imperfect science.

This article explores the major genes that scientists have identified as playing a role in human hair color, how they work together, and what their distribution across populations tells us about human history.

Heritability: How Much of Hair Color Is Genetic?

Before we look at specific genes, it is worth asking a basic question: how much of hair color is actually determined by genetics versus environment?

The answer is: a lot.

Twin studies have consistently shown that hair color is one of the most heritable human traits. A large study of over 20,000 twins, parents, and siblings from the Netherlands Twin Register estimated the broad-sense heritability of hair color between 73% and 99% . This means that the vast majority of variation in hair color between people is explained by genetic differences, not by sun exposure, diet, or other environmental factors.

The same study found that the genetic component included non-additive genetic variance — meaning that interactions between genes (epistasis) play an important role . This is why hair color genetics is not as simple as adding up the effects of individual genes.

The study also found evidence of assortative mating for hair color: people tend to partner with others who have similar hair colors, except for red and black hair, which did not show the same pattern .

The Major Players: Genes Known to Influence Hair Color

Over the past two decades, genome-wide association studies (GWAS) have identified dozens of genetic loci associated with hair color. A recent review noted that hair color has been linked to 123 autosomal loci and 1 locus on the X chromosome .

Here are the most important genes identified so far, what they do, and which hair colors they affect.

Gene	Function	Associated Hair Colors	Key Variants
MC1R	Controls switch between eumelanin and pheomelanin	Red, brown, black	R151C, R160W, D294H
HERC2	Regulates OCA2 expression	Blonde, brown, light vs. dark	rs12913832
OCA2	Controls melanosome pH and function	Brown, blue eyes (indirectly)	rs1800407, rs1800401
SLC45A2	Melanosome membrane protein	Darker pigmentation	rs16891982
KITLG	Melanocyte development and survival	Blonde	rs12821256
IRF4	Regulates melanin production	Blonde, hair graying	rs12203592
TPCN2	Calcium channel in melanosomes	Blonde, brown	rs3829241
SLC24A4	Potassium-dependent sodium/calcium exchanger	Blonde, brown	rs12896399
TYR	Tyrosinase — key enzyme in melanin production	Brown, skin darkness	rs1393350, rs1042602
TYRP1	Helps produce eumelanin	Brown, blonde (Melanesian)	rs1408799, R93C
ASIP	Agouti signaling protein — antagonizes MC1R	Brown, dark hair	rs1015362, rs619865

MC1R: The Master Switch for Red Hair

The MC1R gene (melanocortin-1 receptor) is the most famous player in hair color genetics. It sits on the surface of melanocytes and receives signals that tell the cell which pigment to produce . When MC1R is activated, the melanocyte produces eumelanin (dark pigment). When MC1R is less active — because of certain genetic variants — the melanocyte defaults to producing pheomelanin (red-yellow pigment) .

Variants in MC1R that reduce receptor activity are called RHC alleles (red hair color alleles). The three most common are R151C, R160W, and D294H .

Variant	Effect	Notes
R151C	Impaired MC1R function	One of the most common red hair variants
R160W	Impaired MC1R function	Strongly associated with red hair
D294H	Severely impaired — almost complete loss-of-function	Associated with very strong red phenotypes

A person needs two copies of RHC alleles — either homozygous (two of the same) or compound heterozygous (two different variants) — to have pure red hair . When a person has two RHC alleles, up to 96% exhibit classic red hair.

However, the genetics are not fully simple. People can carry one RHC allele and still have reddish hair, though often lighter or mixed with other shades. And some redheads carry none of the common RHC variants — suggesting that other genes also play a role.

The effect size of MC1R on red hair is substantial. A study of eye, hair, and skin pigmentation found that the rs1805007 variant (T allele) had an odds ratio of 7.44 for red hair — meaning people with this variant are more than seven times more likely to have red hair than those without it .

HERC2 and OCA2: The Duo That Controls Brown and Blonde

If MC1R is the master switch for red hair, HERC2 and OCA2 are the master regulators for brown and blonde hair.

OCA2 (oculocutaneous albinism type II) encodes a protein that helps regulate the pH of melanosomes — the tiny organelles inside melanocytes where pigment is made . The pH of the melanosome affects how much eumelanin is produced. This gene is also the primary determinant of blue versus brown eye color.

HERC2 sits next to OCA2 on chromosome 15 and regulates its expression. The most important variant is rs12913832, which acts as an “enhancer” — it controls how much OCA2 protein is produced. People with one version of this variant have higher OCA2 expression, leading to more eumelanin and darker hair and eyes. People with the other version have lower OCA2 expression, leading to less eumelanin and lighter hair and eyes .

A study of the Polish population found that rs12913832 in HERC2 was highly associated with hair color across all categories — blond, dark, and red — making it one of the most important single predictors of hair color .

A 2009 study confirmed that HERC2 rs12913832 is associated not only with eye color but also with skin and hair color . The same study found evidence of an interaction between MC1R and HERC2 in determining skin and hair color — meaning that these genes do not work independently but influence each other’s effects .

KITLG: The Blonde Hair Gene

The KITLG gene (KIT ligand) plays a critical role in the development and survival of melanocytes . Variants near this gene have been strongly associated with blonde hair in populations of European descent.

The specific variant rs12821256 (C allele) is associated with lighter hair color. A study of hair color in a European population found that this variant had a significant effect on blonde versus non-blonde hair, with an effect size of -0.352 (meaning it pushed hair color toward the lighter end of the spectrum) .

The KITLG variant associated with blonde hair is most common in Northern European populations and shows evidence of recent positive selection — suggesting that it offered some advantage to the people who carried it.

IRF4: The Gene That Affects Both Hair Color and Graying

IRF4 (interferon regulatory factor 4) is a transcription factor that regulates the expression of other genes involved in melanin production . Variants in IRF4 have been associated with both hair color and hair graying .

The specific variant rs12203592 (T allele) is associated with lighter hair color and has also been linked to premature hair graying . This connection makes IRF4 particularly interesting: it is one of the few genes known to influence both the amount of pigment produced during a person’s youth and the timing of pigment loss as they age.

A study of over 5,000 individuals found that IRF4 was one of the genes that gave genome-wide significant hits for blond, brown, and light versus dark hair color .

SLC45A2 and SLC24A4: The Melanosome Transporters

SLC45A2 (solute carrier family 45, member 2) and SLC24A4 (solute carrier family 24, member 4) encode proteins that help transport substances into and out of melanosomes. They are involved in maintaining the correct environment for melanin synthesis.

Variants in SLC45A2 are associated with darker pigmentation. The rs16891982 variant (G allele) is associated with darker hair and has been shown to improve the predictive accuracy of hair color models, particularly for red hair .

SLC24A4 has been associated with blonde and brown hair in multiple studies. A large genome-wide association study found that the rs12896399 variant near SLC24A4 was significantly associated with both eye and hair color .

Notably, variants in SLC45A2 and SLC24A4 have also been associated with melanoma risk, suggesting that the same pigmentation pathways that determine hair color also influence skin cancer susceptibility .

TPCN2: The Calcium Channel

TPCN2 (two-pore channel 2) encodes a calcium channel in the membrane of melanosomes . The pH of melanosomes — and therefore the type and amount of melanin produced — is regulated in part by calcium signaling.

Variants in TPCN2 have been associated with blonde and brown hair in populations of European descent. Like many other hair color genes, TPCN2 variants show evidence of natural selection, suggesting they offered some advantage in the environments where they spread.

TYR and TYRP1: The Enzyme Genes

TYR (tyrosinase) is arguably the most important enzyme in melanin production. It catalyzes the first step in the melanin synthesis pathway: the conversion of tyrosine to dopaquinone . From there, the pathway splits toward eumelanin or pheomelanin.

Variants in TYR are associated with brown hair and skin darkness. The rs1393350 (A allele) is associated with lighter hair and eye color, while the rs1042602 (A allele) is associated with darker pigmentation and has also been linked to freckling .

TYRP1 (tyrosinase-related protein 1) is another enzyme involved in eumelanin synthesis. Variants in TYRP1 are associated with brown hair in European populations. But this gene has a more famous claim to fame: the R93C mutation in TYRP1 is the cause of blonde hair in the Solomon Islands . This is a powerful example of convergent evolution — the same visible trait (blonde hair) arising through completely different genetic paths in different populations.

Gene-Gene Interactions: The Complexity Multiplies

Here is where the story gets truly complex. Genes do not work in isolation. They interact.

Gene Pair	Interaction Type	Effect
MC1R and HERC2	Epistatic	Their combined effect on skin and hair color is different from the sum of their individual effects
MC1R and ASIP	Epistatic	ASIP antagonizes MC1R signaling; variants in both genes together have stronger effects than either alone
SLC45A2 and OCA2	Epistatic	These variants show significant statistical interaction in melanoma risk studies
HERC2 and OCA2	Regulatory	HERC2 controls OCA2 expression; this is not really an interaction but a direct regulatory relationship

A 2009 study confirmed that “there is an interaction between MC1R and HERC2 in determination of skin and hair colour in the studied population sample” . This means that the effect of having a certain MC1R variant depends on which HERC2 variant you also have — and vice versa.

Similarly, a study of melanoma risk found “significant epistatic interactions between SLC45A2 and OCA2 alleles, and MC1R and ASIP alleles” . These interactions accounted for a substantial proportion of the genetic risk for melanoma in the study population.

Tandem Repeats: A New Layer of Complexity

Most genetic studies of hair color have focused on single nucleotide polymorphisms (SNPs) — changes in a single DNA letter. But there is another type of genetic variation that is only now being explored: tandem repeats (TRs).

A 2024 preprint reported the discovery of 16 tandem repeats with effects on different models of hair color, plus two TRs associated with hair color in diverse ancestry groups . Several of these TRs expand or contract the amino acid coding regions of their localized proteins, meaning they could alter protein structure and function.

Importantly, these TRs can predict darker hair color independent of SNP variation. This means that traditional genetic studies that only looked at SNPs may have missed a significant portion of the genetic contribution to hair color.

The preprint notes that this work “adds to the growing body of evidence regarding TR influence on human traits with relatively large and independent effects relative to surrounding SNP variation” .

What These Genes Tell Us About Human History

The distribution of hair color-associated variants across populations tells a story of migration, adaptation, and chance.

The MC1R variants that cause red hair are most common in Northern and Western Europe — particularly in Scotland (13% redheads), Ireland (10%), and Wales. They are rare elsewhere. This suggests that these variants arose in European populations after the out-of-Africa migration and spread through a combination of relaxed selective pressure (less need for dark pigment in northern latitudes) and possibly sexual selection.

The HERC2/OCA2 variants that influence blonde and brown hair show a similar pattern. The “light” alleles are common in Northern Europe and rare elsewhere.

The KITLG variant associated with blonde hair shows clear evidence of recent positive selection in Northern Europe, suggesting it offered some advantage — possibly related to vitamin D synthesis or sexual selection.

The TYRP1 variant that causes blonde hair in the Solomon Islands is completely absent outside Melanesia. It arose independently, showing that evolution can find similar solutions (blonde hair) through different genetic paths in different populations.

What This Means for Understanding Your Hair

The next time you look at your hair in the mirror, consider the genetic symphony playing beneath your scalp.

Hundreds of genetic positions across your genome are working together — some increasing eumelanin, some decreasing it, some shifting the balance toward pheomelanin, some controlling the pH of your melanosomes, some regulating the expression of others. The specific combination of variants you inherited from your parents produces your unique hair color.

If you have red hair, you likely carry two copies of MC1R variants. Your melanocytes are biased toward producing pheomelanin.

If you have black or dark brown hair, you likely carry multiple variants that promote high eumelanin production — in HERC2, OCA2, SLC45A2, and other genes.

If you have blonde hair, you may carry variants in KITLG, HERC2, or IRF4 that reduce eumelanin production.

If your hair is somewhere in between — light brown, dark blonde, auburn — you carry a mix of variants that produce an intermediate phenotype.

None of these combinations is better than another. They are just different. Different solutions to the same problem: how to produce a hair fiber with the right amount of pigment for the environment where your ancestors lived.

And that solution is written, not in a single gene, but in hundreds of them — scattered across your genome, each playing a small part in the symphony that produces the color on your head.

References

Branicki, W., Brudnik, U., & Wojas-Pelc, A. (2009). Interactions between HERC2, OCA2 and MC1R may influence human pigmentation phenotype. Annals of Human Genetics, 73(2), 160–170. https://pubmed.ncbi.nlm.nih.gov/19208107/

Fazzari, V., Moo-Choy, A., Panoyan, M. A., Abbatangelo, C. L., Polimanti, R., Novroski, N. M., & Wendt, F. R. (2024). Multi-ancestry tandem repeat association study of hair colour using exome-wide sequencing. bioRxiv, 2024.02.24.581865. https://pmc.ncbi.nlm.nih.gov/articles/PMC10925195/

Duffy, D. L., et al. (2010). Multiple pigmentation gene polymorphisms account for a substantial proportion of risk of cutaneous malignant melanoma. Journal of Investigative Dermatology, 130(2), 520–528. https://pubmed.ncbi.nlm.nih.gov/19710684/

Hottenga, J. J., et al. (2015). Heritability and genome-wide association studies for hair color in a Dutch twin family based sample. Genes, 6(3), 559–576. http://oa.las.ac.cn/oainone/service/browseall/read1?ptype=JA&workid=JA202211291462765ZK

Rayinda, T., & Tziotzios, C. (2025). The genetic and environmental architecture of human hair traits: a shift toward precision medicine in hair disorders. British Journal of Dermatology. https://www.biosino.org/humanphenomics/pdfView?id=65177444ff824a158fbb4f136ae98f19#1

Siewierska-Górska, A., et al. (2017). Association of five SNPs with human hair colour in the Polish population. Homo, 68(2), 134–144. https://pubmed.ncbi.nlm.nih.gov/28242083/

Fazzari, V., et al. (2024). Multi-ancestry tandem repeat association study of hair colour. openRxiv. https://ouci.dntb.gov.ua/en/works/98ezYgw7/

National Institutes of Health. (2013). Table 3: Association results for pigmentation traits. PMC. https://pmc.ncbi.nlm.nih.gov/articles/PMC3778125/table/tbl3/

Matheny, A. P., Jr., & Dolan, A. B. (1975). Sex and genetic differences in hair color changes during early childhood. American Journal of Physical Anthropology, 42(1), 53–56. https://pubmed.ncbi.nlm.nih.gov/1167738/

Desai, D. D., et al. (2025). Premature hair graying: a multifaceted phenomenon. International Journal of Dermatology, 64(5), 819–829. https://www.ovid.com/journals/ijderm/fulltext/10.1111/ijd.17580

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.

Previous: Red Hair

Next: Different Follicles, Same Body

Leave a comment Cancel reply

The Dragon Remembers

10. The Future of Hair Color

9. The Psychology of Hair Color

Trending

The Dragon Remembers

10. The Future of Hair Color

9. The Psychology of Hair Color

8. The History of Hair Dye