How Hair Color Works

Hair has a simple structure composed of three critical parts: hair shaft, hair cuticle, and hair bulb. The hair shaft is the visible part of the hair that protrudes from the skin. The hair shaft is anchored just beneath the scalp surface thanks to the hair follicle. At the base of the hair follicle sits the hair bulb, which is where living cells divide and create the hair shaft. One type of cell inside the hair bulb directly impacts permanent hair color:

• Melanocytes – Melanocytes are melanin-producing cells that affect bodily pigments including skin, eye, and hair color. As people age, the melanocytes in their hair bulb die, leaving hair shafts gray.

Melanocytes inject the melanin (or pigment) into keratinocytes, which are cells that create keratin. Keratin is the protein that makes up hair, skin, and nails. The melanin that’s inside the hair’s keratin is how hair gets its color.

There are different types of melanin that can change the color of hair:

• Eumelanin is the most prevalent melanin in the human body. This results in black and brown tones and gives pigment to both skin and hair.
• Pheomelanin results in red tones. This melanin is present not only in hair but also gives our lips their pink hue.

What Makes Hair Color What It Is?

What determines hair color is the amount and type of melanin produced by melanocytes. While eumelanin dictates how dark the hair is, pheomelanin controls how red the hair is.

• Someone with dark brown or black hair has up to 95% eumelanin in their hair follicles. However, that doesn’t mean they lack pheomelanin. This lighter, red pigment may be covered up entirely under dark hair, or it may give brown hair a reddish hue in some lights.
• Blonde hair occurs in people who have little eumelanin—but don’t have much pheomelanin, either.
• A red haired person has more pheomelanin than eumelanin. The amount of eumelanin does affect what type of red hair. Auburn hair, for example, has more eumelanin than strawberry blonde hair, which has more eumelanin than fiery red hair.

The whole spectrum of human hair color from champagne blonde to fiery red to charcoal black can be explained by the levels of these two varieties of melanin.

Genetics and Their Role in Hair Color

Put simply, genes impact how much of each type of melanin is produced within the hair follicles.

The melanocortin 1 receptor(MC1R) is a key protein that determines which kind of melanin (eumelanin or pheomelanin) melanocytes produce at the root of the hair bulb.

As you may recall from high school biology, genes come in alternate forms (called alleles). These MCR1 alleles work together to form hair color:

• Most people have two functioning MC1R genes (one from each parent). When this gene is “on,” it stimulates the production of eumelanin. Having two functioning alleles is so common, 90% of people have brown hair.
• Some people have one MC1R gene that is “off.” This deactivated gene results in less production of eumelanin. This can result in lighter shades of hair, like blonde hair.
• If both copies of the MC1R gene are off, this results in little to no eumelanin production. Should there be an abundance of pheomelanin, people with this genetic profile will have red hair.

Mentioned above, this is just one gene out of many that determine hair color. Scientists have found up to a dozen genes that play some role in a person’s locks—though the individual gene’s level of involvement is still being understood.

Why Does a Baby’s Hair Color Change?

After birth, baby hair is now exposed to a new source of energy. The sun. This new source may affect baby’s eye color[MS1], skin tone (e.g., tanning), and his hair color.

While the sun directly impacts vitamin D production, it’s not straightforward why sunlight would cause your baby’s hair to darken over time. After all, sunlight’s UV radiation is known to bleach hair by oxidizing melanin and stripping its color.

While we don’t fully understand the reasons why light hair tends to darken over time, scientists theorize that changing hormone levels regulate the production of both eumelanin and pheomelanin, increasing the amount of eumelanin produced over time.

When Does a Baby’s Hair Color Change?

Similar to when a baby’s hair texture changes, when a baby’s hair color will change can depend on a few factors. Both baby boy and girl hair can change color through their first few birthdays. Though, by the age of 5, most children will have their adult hair color. However, in some cases, continued eumelanin production can increase over time, darkening hair well into adolescence.

So when does a baby’s hair change color? It’s hard to say exactly when. But the factors involved include: hair color genetics, sun exposure, and nutrition (though genetics play the most significant role). As your child’s hair changes over months and years, you’ll go on a journey of discovery together.

The Truth About Dominant and Recessive Genes

You may have learned in high school that traits like hair color, eye color, and more are determined by dominant and recessive genes. For hair color, the theory goes:

• Each parent carries two alleles (gene variants) for hair color. Blonde hair is a recessive gene and brown hair is a dominant gene.
• A brunette may have two brown hair alleles or one brown allele and one blonde allele. However, a blonde person must have two recessive blonde genes.
• If two brunette parents both have a recessive blonde gene, there’s a 25% chance they’ll each pass down their recessive gene, resulting in a blonde child.
• Because blonde people carry only the recessive blonde genes, they can only have blonde children.

However, as you now know, it’s more complicated than that. After all, this “Punnett Square” model only considers the alleles that regulate the amount of eumelanin produced (MC1R). It doesn’t acknowledge the SLC7A11 gene which controls pheomelanin production and red hair, or any other genes.

Because more than one gene is involved in hair color, a simple theory of dominant and recessive traits doesn’t quite capture the whole picture. You might not know your baby’s hair color yet, but you may find more answers than you ever thought possible with SneakPeek. For a deeper dive into the fascinating traits inherited from your mother, check out our detailed genetics blog.

Does Hair Color Correlate with Eye Color?

Hair and eye color are often linked because they are influenced by some of the same genetic pathways. Both traits depend on the production and distribution of melanin, a pigment that determines the darkness or lightness of hair, skin, and eyes. Genes like OCA2 and HERC2, which play a key role in determining eye color, can also impact melanin levels in hair, leading to a correlation between the two traits. For instance, lighter hair colors are more likely to accompany blue or green eyes, while darker hair often correlates with brown eyes. However, the genetic interplay is complex, and variations in other genes can result in unexpected combinations. Questions such as ‘What color eyes will my baby’s hair be?‘ are common due to this genetic complexity.

The Influence of Ethnicity on Hair Color

Hair color is one of the many physical traits influenced by genetic diversity within and across ethnic groups. Variations in genes such as MC1R, which affects melanin production, lead to the wide range of hair colors observed globally. For example:

• Populations of European descent tend to exhibit the greatest variety of hair colors, ranging from blonde to red to dark brown, due to higher genetic diversity in melanin-related genes.
• Asian and African populations typically have darker hair shades, as genetic adaptations over time favored eumelanin, which provides increased UV protection.

These differences highlight how genetics and evolutionary pressures have shaped hair color across human populations. Genetic diversity plays a key role in the expression of physical traits, including hair color, reflecting each group’s unique evolutionary history.

Fun Facts About Hair Color

1. Red Hair Is the Rarest Natural Hair Color: Only about 1-2% of the world’s population has red hair, caused by mutations in the MC1R gene. Both parents must carry this recessive gene for their child to have red hair.
2. Blonde Hair in Melanesian Populations: In certain Melanesian communities, blonde hair occurs naturally due to a mutation in the TYRP1 gene, completely separate from the genes responsible for blonde hair in Europeans.
3. Black Hair Is the Most Common Hair Color Worldwide: Black hair is dominant globally due to high levels of eumelanin, especially in populations from Africa and Asia.
4. Natural White or Platinum Hair: Natural white or platinum blonde hair is extremely rare and most often associated with conditions like albinism, where melanin production is significantly reduced or absent.
5. Gray Hair Isn’t Just About Aging: The appearance of gray hair results from a reduction in melanin production over time. However, certain genetic factors can cause premature graying, even in young individuals.

These fascinating variations showcase the intricate interplay of genetics and environment in determining hair color.

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