Why does hair turn white or grey? Last updated: 1 March 2026

Why Does Hair Turn White or Grey? The Real Science Behind Silver Strands

Grey hair is one of the most visible signs of aging, but the biology behind it is far more intricate than “getting old” or “being stressed.” In each strand, stem cells, pigment chemistry, genetics and oxidative stress all intersect to decide when colour fades — and whether it might come back.

Grey hair appears when pigment cells inside each follicle stop delivering melanin to the growing hair shaft over successive growth cycles.

How Hair Gets Its Colour

Each hair grows from a follicle that contains specialized pigment‑making cells called melanocytes.​

• Melanocytes sit next to the hair matrix and pump melanin pigment into the shaft during the anagen (growth) phase.​

• A nearby reservoir of melanocyte stem cells (McSCs) continually replenishes working melanocytes across multiple hair cycles.​

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As long as this mini “pigment factory” is supplied with healthy stem cells and the enzymes to make melanin, hair retains its natural colour.

Aging: Stem‑Cell Exhaustion and Oxidative Stress

With age, two linked processes gradually undermine the follicle’s pigment system.

1. Melanocyte stem cells lose function or disappear

   • Ageing and DNA damage reduce the pool of McSCs, so fewer new melanocytes are available each growth cycle.​

   • Mouse and human studies show that defects in McSC self‑maintenance, rather than the death of mature melanocytes alone, are a key driver of greying.​

2. Oxidative stress builds up inside the follicle

   • Melanin production naturally generates reactive oxygen species (ROS); over time, the follicle’s antioxidant defences weaken.

   • Grey/white hairs accumulate high levels of hydrogen peroxide while antioxidant enzymes such as catalase decline, allowing peroxide to damage tyrosinase, the rate‑limiting enzyme for melanin synthesis.

Even if some melanocytes survive, this oxidative environment can “bleach” the hair shaft from within and impair pigment production.

Can Stress Really Turn Hair Grey?

Specialised melanocytes at the base of each follicle transfer melanin into the hair shaft; when their stem cells are depleted, new hairs emerge grey or white.

For decades, stress‑induced greying was folklore; now it has a mechanistic explanation.

• A landmark Nature study in mice showed that acute stress activates sympathetic nerves that innervate the follicle niche.

• These nerves release a burst of norepinephrine, which drives quiescent melanocyte stem cells to rapidly proliferate, differentiate and then vacate the niche, permanently depleting the stem‑cell pool.

Complementary human work suggests the story is nuanced:

• Human “hair pigmentation profiling” has shown that individual hairs can lose and later regain colour in step with major life stressors, indicating that some early greying is reversible while the pigmentary unit remains structurally intact.​

• Once stem cells are fully exhausted or niches are structurally damaged, however, later hairs grow in white and stay white.

In short: severe or repeated stress can accelerate greying by draining the stem‑cell reservoir, but milder, early changes may sometimes be reversible.

Genetics: Why Some People Grey Earlier Than Others

When your first grey appears is strongly influenced by your genes.

• Large genome‑wide association studies have identified multiple loci linked to greying, including variants in IRF4, a transcription factor that helps regulate melanin production and storage.

• A UCL‑led study estimated that one common IRF4 variant explains roughly 30% of the variation in greying timing, with the rest shaped by age, environment and other genes.​

Population data also reveal consistent ethnic patterns:

• On average, people of European ancestry tend to notice greys in their mid‑30s, people of Asian ancestry in their late‑30s, and people of African ancestry in their mid‑40s, reflecting differences in genetic background and follicular resilience.​

These are averages, not rules — but they help clinicians define “premature greying” relative to a person’s ancestry.

Lifestyle Factors: What Really Influences Greying?

Lifestyle cannot completely override genetics and time, but certain factors are associated with earlier greying.

Smoking

• A systematic review of observational studies found that smokers are roughly two to four times more likely to show premature greying than non‑smokers, likely due to added oxidative stress and vascular effects on the follicle.

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Health Conditions and Deficiencies

Clinical reviews link some medical issues to premature greying:​

• Vitamin B12 deficiency

• Thyroid dysfunction

• Certain cardiometabolic conditions and autoimmune diseases

In these cases, treating the underlying condition can sometimes slow progression or allow partial re-pigmentation, particularly if the hair follicle’s pigmentary unit is still structurally intact.​

Psychological stress can activate sympathetic nerves and increase oxidative damage in the follicle, accelerating the loss or dysfunction of pigment‑producing stem cells in some people.

Myths to Treat Cautiously

• Occasional poor sleep, a single argument, or one stressful week are unlikely on their own to cause permanent white hair.

• Extreme claims that specific supplements, topical products, or diets can “reverse all grey hair” are not supported by controlled human trials; current evidence suggests only limited, context‑dependent reversibility.

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For most people, grey hair reflects a long‑running interplay of genetic predisposition, cumulative oxidative damage, stem‑cell exhaustion and life‑course stress, not a simple verdict on lifestyle.

Is Grey Hair Reversible?

Based on current evidence, there are three broad scenarios:

1. Early, reversible greying in intact follicles

   • Some hairs can regain pigment after stressors resolve or metabolic issues are treated.

2. Functional impairment with surviving melanocytes

   • Targeted antioxidants or future therapies might recover some pigment, but data are still emerging.

3. Complete stem‑cell depletion and structural ageing

   • Once melanocyte stem cells are lost and niches remodelled, regrowth is typically permanently white.

Researchers are exploring topical antioxidants, stem‑cell supportive strategies and gene‑targeted approaches, but these remain experimental.

Key Takeaways: Why Hair Turns White or Grey

• Melanocyte stem cells and melanin enzymes keep hair coloured; ageing, genetics and damage gradually undermine both.

• Oxidative stress and hydrogen peroxide buildup inside the follicle can chemically bleach hair and disable pigment enzymes.

• Stress links to greying through sympathetic‑nerve activation and norepinephrine, which can deplete pigment stem cells in animal models and correlate with pigment changes in human hairs.

• Genes such as IRF4 strongly influence when greying begins, while ancestry shapes average timelines across populations.

• Smoking, some deficiencies and systemic disease can shift greying earlier, but they explain only a fraction of cases.

  
  

Grey hair is, above all, a visible record of how your follicles’ pigment systems have navigated time, genetics and stress — not a simple on/off switch or a verdict on personal choices.

Beth Thompson

© 2026 LUX SYMBOLICA®

Citations

1. Rosenberg AM et al. Quantitative mapping of human hair greying and reversal in relation to life stress. eLife. 2021.

2. Hsu Y‑C et al. Hyperactivation of sympathetic nerves drives depletion of melanocyte stem cells. Nature. 2020.

3. Schallreuter KU et al. Senile hair graying: H₂O₂‑mediated oxidative stress affects human hair color. FASEB J. 2009.

4. University of Bradford/Mainz press materials on hydrogen peroxide, catalase and greying.

5. Ito M et al. Aging melanocyte stem cells and gray hair; NYU/NIH coverage of “stuck” McSCs.

6. Zhang Y et al. Gray Hair: From Preventive to Treatment. 2025.​

7. Reddy S et al. Premature Graying of Hair: A Comprehensive Review and Recent Updates. 2024.​

8. Tobin DJ. The biology of human hair greying. Exp Dermatol. 2019.​

9. Trüeb RM et al. Hair Aging in Different Races and Ethnicities. J Clin Aesthet Dermatol. 2020.

10. Adhikari K et al. Discovery of a gray hair gene (IRF4) in humans. UCL/Mayo summaries.

11. Pratt CH et al. The Effects of Smoking on Hair Health: A Systematic Review.