What Makes Hair Gray?

Hair turns gray when the pigment-producing cells inside each follicle gradually stop working. Those cells, called melanocytes, inject pigment into the hair shaft as it grows. Over time they slow down, produce less pigment, and eventually shut down. The result is a hair that still grows normally but has no color left in it — which is what we see as gray or white.

That process is real and well understood. What causes it to start at 25 for one person and 55 for another is where the science gets more interesting, and where a lot of popular claims fall apart.

What Makes Hair Gray?

Each hair follicle contains a small reservoir of melanocyte stem cells. During the growth phase of a hair, these stem cells mature into melanocytes, which then manufacture two pigments: eumelanin (brown to black) and pheomelanin (red to yellow). The mix determines your natural hair color.

Graying happens when that stem cell reservoir becomes depleted or stops producing mature melanocytes. Without fresh melanocytes, the follicle keeps building hair but has no pigment to add. The hair comes out transparent, which reads as gray against dark hair and white against light hair.

Research published in Nature in 2023 identified one mechanism behind this: melanocyte stem cells can get stuck in a state where they stop maturing but also do not die off. They remain lodged in the follicle without doing their job. The study authors described this as stem cells becoming “stuck” rather than simply running out. That is a meaningful distinction, though it does not yet translate into a way to reverse graying.

Another line of research points to oxidative stress. Hair follicles accumulate hydrogen peroxide over time, and the enzyme that normally breaks it down (catalase) becomes less active. Hydrogen peroxide damages the melanocytes and interferes with pigment production. This has been measured in graying hair follicles, though whether it is a cause or a consequence of the process is still debated.

Why Does Graying Start at Different Ages for Different People?

Genetics is the single biggest factor. If your parents went gray early, you likely will too. Researchers have identified specific genes linked to hair graying, including one called IRF4, which also influences hair, skin, and eye color. This is why graying patterns tend to run in families.

For people of European descent, graying often begins in the early 30s. For people of African or Asian descent, it typically starts later, often in the late 30s or early 40s. These are general patterns, not rules. Some people in their 20s have significant gray, and some people in their 50s have very little.

Men and women gray at roughly similar rates, though men often notice it first at the temples and women often notice it first at the part line. The order in which hair grays is fairly consistent: temples and sides first, then the top, then the back. Body hair, eyebrows, and eyelashes usually hold their color much longer.

Can Stress Turn Hair Gray?

Yes, but the effect is probably smaller and slower than most people assume. The “someone went gray overnight” story is a myth — hair that has already grown out of the follicle cannot change color. What can happen is a condition called telogen effluvium, where a stressful event causes a large number of pigmented hairs to shed at once, leaving the gray hairs behind. That creates the appearance of sudden graying.

That said, stress does appear to affect the process. A study published in Nature in 2020 found that stress activates the sympathetic nervous system, which in turn depletes melanocyte stem cells in mice. The researchers also analyzed human hair and found evidence consistent with stress-related pigment loss. The effect in humans was real but modest — not the dramatic overnight change people describe.

Chronic stress also contributes to oxidative stress, which as noted above can damage melanocytes over time. So stress likely plays a supporting role. It is not the main driver for most people.

What About Nutrition and Vitamin Deficiencies?

Severe deficiencies in vitamin B12, iron, copper, or thyroid hormone can cause premature graying. This is well documented in clinical case reports, particularly for B12 deficiency and pernicious anemia. When the deficiency is corrected, some people regain pigment — but this is not guaranteed, and it depends on how long the deficiency lasted and whether the melanocytes are still functional.

For people who are not deficient, there is no strong evidence that taking supplements prevents or reverses graying. Some small studies have looked at vitamin B12, folic acid, and zinc in people with premature graying, but the results are mixed and the studies are small. No large trial has confirmed that supplementation helps in people with normal levels.

Copper is worth a specific mention. Copper is required for tyrosinase, the enzyme that produces melanin. Very low copper can affect hair color. But copper deficiency is rare in people eating a normal diet, and excess copper is toxic. Taking copper supplements without a diagnosed deficiency is not a good idea.

Does Smoking or Illness Cause Gray Hair?

Smoking is consistently associated with premature graying in observational studies. The mechanism is likely oxidative stress — cigarette smoke generates free radicals that damage melanocytes. The association is real, though the effect size is moderate and hard to separate from other lifestyle factors.

Several medical conditions are linked to early graying:

• Thyroid disorders — both hypothyroidism and hyperthyroidism have been associated with premature graying
• Vitiligo — an autoimmune condition that destroys melanocytes in skin and hair
• Alopecia areata — can cause regrowing hair to come in white or gray
• Pernicious anemia — B12 deficiency from poor absorption
• Progeroid syndromes — rare genetic conditions that cause accelerated aging

If graying happens suddenly, is accompanied by other symptoms like fatigue, hair loss, or skin changes, or starts unusually early with no family history, it is worth talking to a doctor. These conditions are treatable, and in some cases the pigment loss can be partially reversed.

Can Gray Hair Be Reversed?

Sometimes, but rarely, and not reliably. Documented cases exist where people with B12 deficiency, thyroid disease, or alopecia areata regained hair color after treatment. These cases are the exception, not the rule.

The 2023 Nature study on stuck stem cells has raised interest in whether graying could eventually be reversed pharmacologically. But that research is at an early stage. No treatment currently exists that reliably restores pigment to gray hair, and any product claiming to do so should be viewed with skepticism.

What does not work: topical dyes that claim to “restore” melanin production, most supplements marketed for gray hair, and “anti-gray” shampoos. None of these have clinical evidence supporting their claims. Hair dye covers gray hair effectively, but it does not change what the follicle is doing.

Is Gray Hair Different From Pigmented Hair?

Gray hair is structurally different in a few ways that people often notice. It tends to be coarser and drier because the follicle produces less sebum as it ages, and the cuticle — the outer layer — is often thinner. Gray hair also tends to be more resistant to styling and can feel wiry.

The texture changes are not caused by the loss of pigment itself. They come from the same aging process affecting the follicle. Some people with gray hair find it behaves differently than their pigmented hair did, which is why hair care routines often need adjusting.