What Causes Gray Hair? Can It Be Reversed? (2026 Research)

Quick answer: Gray hair happens when the pigment cells in your hair follicles stop making melanin, mostly because of genes and age. Stress can speed it up: a 2020 study in mice showed how stress nerves wipe out pigment stem cells, and a 2021 study found some gray hairs in people regained their color when stress eased. Smoking and low vitamin B12, iron or vitamin D are also linked to early graying. Fixing a real deficiency or reducing stress may slow it, but no supplement or serum has been shown to reverse established gray hair in people.

Gray (or grey) hair is one of the most searched beauty questions, and one of the most oversold. We went through the research on what causes it, whether it can be reversed, and which products are worth buying.

What Causes Gray Hair?

Each hair follicle has pigment cells called melanocytes that color the hair as it grows. They’re refilled by a small pool of melanocyte stem cells. When that pool runs out, or the cells stop working, new hair grows in without pigment and looks gray or white. These are the main reasons it happens.

Cause	What the research shows	Can you change it?
Genes and age	The biggest factor. Timing tends to run in families.	No
Stem cell damage	DNA damage pushes pigment stem cells to mature and disappear (2025, Nature Cell Biology, in mice)	Not yet
Stress	Stress nerves deplete pigment stem cells in mice; some human hairs regained color when stress eased	Partly
Hydrogen peroxide buildup	Gray hair follicles build up hydrogen peroxide as natural defenses decline	Not with current products
Low B12, iron, vitamin D	Linked to premature graying in observational studies	Yes, if you’re deficient
Smoking	Smokers were about 2.5 times more likely to gray before 30 in one study	Yes

Your Pigment Stem Cells Run Out

A 2025 study in Nature Cell Biology by researchers at the University of Tokyo found that when melanocyte stem cells suffer certain DNA damage, they mature and are lost instead of renewing. In mice, this protected against melanoma but led to graying. It helps explain why graying is usually permanent once the stem cell pool is gone.

Does Stress Cause Gray Hair?

Yes, it can speed it up. A 2020 Harvard study in Nature showed that in mice, stress activates sympathetic nerves that release noradrenaline into the hair follicle, which rapidly burns through the pigment stem cells. That was in mice, though.

In people, a 2021 study in eLife from Columbia University mapped pigment along single hairs and matched it to diaries of life stress. Some gray hairs regained their color at the root when stress went down. This only happened in some hairs and some people, and it’s most likely when graying has just started.

Hydrogen Peroxide Builds Up in the Follicle

A 2009 study in the FASEB Journal found that gray hair follicles contain high levels of hydrogen peroxide, along with lower levels of catalase, the enzyme that normally breaks it down. The peroxide interferes with pigment production. This finding is the basis for many “catalase” supplements, but taking catalase by mouth hasn’t been shown to reach the follicle or restore color.

Vitamin and Mineral Deficiencies

Several observational studies link premature graying to low nutrient levels. For example, a 2016 study of young adults in India found lower ferritin (iron stores) and vitamin B12 in people who grayed before 25. Low vitamin D, copper and calcium have also been reported. These studies show a link, not proof, and correcting a deficiency helps most when graying is early and caused by that deficiency.

Smoking

In a 2013 study of 207 people, smokers were about two and a half times more likely to start graying before age 30 than non-smokers. Smoking adds oxidative stress, which is one plausible reason.

Can Gray Hair Be Reversed?

Usually not, once it’s established. Here’s what the evidence supports:

• Possibly reversible: early graying linked to a real deficiency (B12, iron, vitamin D) once it’s corrected, and some stress-related graying when stress eases.
• Not reversible with current products: age-related and genetic graying, where the pigment stem cells are gone.
• Promising but untested in humans: in a 2025 Nagoya University mouse study, luteolin, an antioxidant found in celery, broccoli and peppers, kept mice bred to go gray from graying. No human trials yet.

If you’re graying before about 30, it’s worth asking your doctor about a blood test for B12, ferritin and vitamin D, and checking your thyroid, since thyroid problems are also linked to early graying.

Purple Shampoo for Gray Hair: What It Does

Check the current price of Clairol Shimmer Lights Purple Shampoo

Purple shampoo doesn’t stop or reverse graying. What it does is cosmetic: gray and white hair often picks up a yellow or brassy tint, and the violet pigment in purple shampoo cancels that out, because purple and yellow sit opposite each other on the color wheel. The result is brighter, cleaner-looking silver.

Clairol Professional Shimmer Lights is one of the longest-running and most-reviewed purple shampoos, made for blonde, silver and gray hair. There’s also a matching Shimmer Lights purple conditioner. Tips: use it once or twice a week rather than every wash, and rinse sooner if your hair is very light, because purple shampoo can leave a lilac tint if left on too long.

Gray Hair Supplements and Serums: What to Skip

• Vitamin B12: only helps if you’re deficient. If a blood test shows low B12, a basic supplement like Nature Made Vitamin B12 is inexpensive, but your doctor should guide the dose.
• Catalase pills: no good human evidence that oral catalase reaches the hair follicle or restores color.
• Biotin: no evidence it prevents or reverses gray hair.
• Fo-ti (He Shou Wu): often sold as a gray hair remedy, but the NIH’s LiverTox database lists it as a cause of acute liver injury, which can be severe. We recommend avoiding it.
• Anti-gray serums: we found no published human trials showing a topical serum restores pigment in established gray hair.

The PrimeDigger Verdict

Gray hair is mostly genes and time. You can’t stop that, but you can avoid speeding it up: don’t smoke, manage stress, and check for B12, iron and vitamin D deficiency if you’re graying early. Skip supplements and serums that promise to reverse it, and steer clear of fo-ti. If you like your gray, a purple shampoo once or twice a week keeps it bright.

Red light devices are marketed for thinning hair, not for gray hair. See our research on whether red light therapy devices work. Curious how supplement labels oversell? See our research on which creatine gummies are worth buying.

Want the deeper investigation? Our ebook The Supplement Scam Bible shows how supplement labels, dosage claims and “clinically proven” wording mislead, and how to read a label for what it actually says. Get the ebook ($19) → See all our ebooks →

This article is for general information, not medical advice. If you’re graying very early or suddenly, talk to your doctor. Read our Health Disclaimer.

Frequently Asked Questions

Sources

• Zhang et al. (2020), Nature: Hyperactivation of sympathetic nerves drives depletion of melanocyte stem cells
• Rosenberg et al. (2021), eLife: Quantitative mapping of human hair greying and reversal in relation to life stress
• Mohri et al. (2025), Nature Cell Biology: Antagonistic stem cell fates under stress govern decisions between hair greying and melanoma
• Wood et al. (2009), FASEB Journal: Senile hair graying, H2O2-mediated oxidative stress affects human hair color
• Daulatabad et al. (2016), International Journal of Trichology: premature graying and low ferritin, B12 and HDL
• Zayed et al. (2013), Indian Dermatology Online Journal: Smokers’ hair, does smoking cause premature hair graying?
• Nagoya University (2025): Luteolin may contribute to the prevention of hair graying (mouse study)
• NIH LiverTox: Polygonum multiflorum (fo-ti, He Shou Wu)