Melanin is the natural pigment that gives hair its color, from the deepest black to the lightest blonde. It’s produced by specialized cells in your hair follicles and deposited into each strand as it grows. The type and amount of melanin your body makes determines your exact shade, and changes in melanin production over time are what cause hair to go gray.
Two Types of Melanin, Countless Shades
Your hair color comes from a combination of two distinct forms of melanin: eumelanin and pheomelanin. Eumelanin is a dark pigment responsible for brown and black tones. Pheomelanin produces red and yellow tones. Every natural hair color is the result of these two pigments mixed in different ratios.
Black and dark brown hair contains large amounts of eumelanin with relatively little pheomelanin. Blonde hair has very small amounts of both. Red hair is the result of high pheomelanin and low eumelanin, which is why it’s the rarest natural color. Light brown and auburn shades fall somewhere in between, with moderate levels of both pigments working together.
How Melanin Gets Into Your Hair
Melanin is manufactured by cells called melanocytes, which sit deep in the hair follicle bulb, the rounded structure at the base of each strand. A relatively small number of these melanocytes produce extraordinary amounts of pigment, year after year, enough to color scalp hairs that can grow over a meter long. The pigment is made inside tiny packages called melanosomes, which are then physically transferred to neighboring cells (keratinocytes) that build the growing hair shaft.
This transfer happens only during the active growth phase of hair, known as anagen. The melanin ends up primarily in the cortex, the thick middle layer of the hair strand that gives it both strength and color. Very little pigment reaches the thin outer cuticle. Once melanin is locked into the hair fiber, it stays there. Your hair strand itself doesn’t change color on its own; any color change you see in a growing strand reflects what was happening inside the follicle at the time that section was produced.
Genetics Control the Color
The best-studied gene involved in hair color is MC1R, which provides instructions for a receptor on the surface of melanocytes. When this receptor is activated, it triggers a chain of chemical reactions that push the cell to produce eumelanin, the darker pigment. When the receptor is inactive or blocked, the cell defaults to making pheomelanin instead.
Variants in the MC1R gene are the primary reason some people have red hair. But MC1R is just one piece of the puzzle. Researchers have identified dozens of other genes that influence how much melanin is made overall, how it’s packaged, and how it’s distributed within the hair shaft. That’s why hair color runs in families but doesn’t always follow simple inheritance patterns. Two brown-haired parents can have a blonde child if both carry the right combination of gene variants.
What Melanin Does Besides Color
Melanin isn’t just decorative. Inside the hair shaft, it acts as a natural sunscreen by absorbing and filtering ultraviolet radiation. This protects the structural proteins in your hair from breaking down under sun exposure. Black hair experiences the least UV damage because its high eumelanin content absorbs the most radiation. Lighter hair, with less melanin, is more vulnerable to sun-related protein degradation and color fading.
There’s a tradeoff, though. Melanin itself gradually degrades as it absorbs UV light, which is why sun exposure can subtly lighten natural hair color over time. The pigment essentially sacrifices itself to protect the hair’s internal structure.
Why Hair Turns Gray
Graying happens when melanocytes in the follicle slow down or stop producing pigment. Without melanin being deposited, new hair grows in white. A mix of pigmented and unpigmented strands on your head creates the overall appearance of gray.
One well-established factor is oxidative stress within the follicle. Your body naturally produces hydrogen peroxide as a byproduct of cellular activity, and in younger people, an enzyme called catalase breaks it down into water and oxygen. As you age, catalase levels drop, and so do levels of repair enzymes that fix hydrogen peroxide damage. The resulting buildup of hydrogen peroxide inside the follicle interferes with melanin production, essentially bleaching the hair from the inside.
Genetics plays the largest role in determining when graying begins. If your parents went gray early, you likely will too. But lifestyle factors, particularly stress, also contribute.
Stress, Graying, and Reversal
A 2021 study from Columbia University provided some of the first concrete evidence that psychological stress can turn individual hairs gray, and that the process can sometimes reverse. Researchers analyzed individual hairs from 14 volunteers by slicing them into tiny segments, each representing roughly one hour of growth. This allowed them to pinpoint exactly when color changes occurred along a single strand.
Some gray hairs naturally regained their original color. In one striking case, a participant went on vacation and five separate hairs reverted from gray to dark during that same period. The researchers tracked changes in about 300 proteins that shifted when hair color changed, and their analysis pointed to stress-related changes in mitochondria (the energy-producing structures inside cells) as a likely mechanism.
There’s an important caveat. The researchers believe hair needs to be near a biological threshold before stress can push it over into graying. For someone in middle age whose follicles are already close to that tipping point, a stressful period might trigger gray hairs, and stress relief might bring color back. But reducing stress won’t restore color in a 70-year-old who has been gray for years, and adding stress to a 10-year-old’s life won’t be enough to overwhelm their robust melanin production.
What Happens to Melanin During Bleaching
Chemical hair bleaching works by breaking down melanin molecules through oxidation. The two types of melanin respond differently to this process. Eumelanin breaks down more easily than pheomelanin. As eumelanin’s chemical structure degrades, it shifts in the colors it reflects, moving from dark brown through red-orange and then to yellow tones.
Because pheomelanin resists breakdown longer, it holds onto its natural red and yellow hues even as eumelanin is being destroyed. This creates a stage during bleaching when the warm tones from degrading eumelanin overlap with the still-intact pheomelanin, producing an intense brassy, orange warmth that hairstylists sometimes call the “Ring of Fire.” It’s the reason dark hair almost always passes through an orange phase on its way to blonde, and why toning products are needed to neutralize that warmth.
This chemistry also explains why naturally dark hair is harder to lighten evenly. There’s simply more eumelanin to break down, and pheomelanin lingers stubbornly throughout the process. Repeated bleaching sessions are often necessary, each one degrading more pigment but also damaging the hair’s protein structure along the way.