№ 01 · Journal

Why hair turns grey.

Hair greying is not a single event. It is a cascade across the hair follicle's biology — and only at that resolution does the logic of a real response become legible.

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The cascade of greying.

Hair greying — canities, in clinical shorthand — has long been filed away as an inevitable sign of age, or blamed on stress, or simply time. Recent research tells a more specific story. Greying is not caused by a single event. It is a cascade: a network failure in which multiple biological systems in the hair follicle break down in parallel. A problem of systems biology.

What is happening, at the microscopic level, for a strand to lose its colour? A set of failures compound. The reservoir of pigment stem cells is depleted and paralysed. Stress signalling surges. Oxidative bleach accumulates. And the underlying machinery collapses — from missing pigment building blocks to metabolic errors to a weakening of the hair structure itself.

The pigment factory.

The central cause is the failure of the follicle's pigment stem-cell reservoir — the melanocyte stem cells, or MSCs. To understand why, start with how hair colour is made.

The factory.

Each hair follicle is a microscopic pigment factory, running a complex production line every minute, for decades.

The workers.

Inside the factory, specialised cells called melanocytes create the pigment. They are short-lived and die off after every hair cycle.

The paint.

The workers produce melanin, which is continuously infused into the growing hair shaft, locking in its colour.

The seed bank.

To replace the dead workers, the follicle relies on a protected reservoir of stem cells (MSCs) that must mobilise to restock the factory floor.

The central cause of hair greying is the critical failure of this seed bank.

When the bank stops delivering new workers, the hair grows unpigmented — grey, then white. The latest research shows this failure is not random. Six interconnected biological drivers govern the cascade.

§ 01.

Stem-cell depletion & signalling failure.

The foundational driver. The MSC reservoir is designed to renew pigment throughout life. With age, the system can fail in two ways.

Depletion.

The finite reservoir of MSCs gradually runs out through accumulated DNA damage and replicative stress [1].

Dysfunction.

In 2023, researchers in Nature showed that many MSCs become “stuck” in their niche [2]. They remain alive but lose the mobility and responsiveness needed to reach the pigment-production zone. The cells no longer receive the key molecular cues — Wnt and Endothelin-1 — that normally coordinate their activation. As this signalling balance deteriorates, MSCs stay locked in an immature state, unable to regenerate colour [8], [9].

Go deeper

Primary sources

[1]
Nishimura, E. K., et al. (2005) — ScienceShowed greying results from melanocyte stem-cell depletion.
[2]
Sun, Q., et al. (2023) — NatureIdentified the “stuck” MSC dysfunction mechanism.
[8]
Chen, J., et al. (2022) — Frontiers in PhysiologyReviewed Wnt/β-catenin imbalance and its role in MSC homeostasis and greying.
[9]
Iida, M., et al. (2024) — AntioxidantsShowed luteolin restores Endothelin-1 signalling in keratinocytes.

Chronic stress-hormone load.

This is not a myth. A 2020 Harvard study showed exactly how intense stress can cause permanent greying. The step that empties the pigment reserve is not cortisol, as long assumed — it is a direct consequence of the fight-or-flight response itself, via noradrenaline released from sympathetic nerves. Cortisol may contribute at the margins; it is not what drives the depletion.

Acute stress.

Activates the sympathetic nerves wrapped around every hair follicle.

Noradrenaline burst.

The nerves release a burst of noradrenaline directly into the MSC niche.

Overactivation.

This flood forces the dormant stem-cell population to activate and differentiate all at once.

Depletion.

The “bank run” rapidly empties the stem-cell reservoir [3].

Go deeper

Primary sources

[3]
Zhang, B., et al. (2020) — NatureThe foundational paper on stress-induced MSC depletion via noradrenaline.

Substrate & co-factor insufficiency.

Even with a healthy seed bank, the factory cannot make paint without a supply chain. Two bottlenecks matter.

Missing raw material.

The core building block for melanin is the amino acid L-Tyrosine. Without it, the factory has nothing to make pigment from [4].

Missing key.

The enzyme that turns L-Tyrosine into melanin — tyrosinase — is copper-dependent. Without Copper, the machine will not turn on. Low serum copper is directly linked to premature greying [5].

Go deeper

Primary sources

[4]
Slominski, A. T., et al. (2004) — Physiological ReviewsDetails L-tyrosine's role in melanogenesis.
[5]
Fatemi Naieni, F., et al. (2012) — Biological Trace Element ResearchLinks low copper to premature greying.

§ 04.

Impaired methylation & metabolic support.

Hair follicles are among the most metabolically active tissues in the body. Two processes govern that activity — energy metabolism, and methylation. Both can stall.

Energy metabolism.

Driven by B-vitamins — particularly Pantothenic Acid (B5) and B6 — which fuel the cellular energy needed for pigment production.

Methylation.

The process that reads DNA and toggles genes. Depends entirely on B12 and Folate (B9). When it fails, pigment-making falters and homocysteine builds up — adding cellular stress. B12 and Folate deficiencies are strongly linked to pigmentation issues [6], [7].

Go deeper

Primary sources

[6]
Daulatabad, D., et al. (2017) — International Journal of TrichologyLinks low B12, folate, and biotin to premature canities.
[7]
Nair, D., Prathap, P., & Asokan, N. (2022) — Pigment InternationalLinks high homocysteine and low B12 or folate to melanocyte dysfunction.

§ 05.

Structural integrity deficits.

If the factory building is weak, the pigment cannot be properly transferred or held.

Keratin supply.

The hair shaft is made of the protein keratin. Nutrients like Biotin (B7) and Pantothenic Acid (B5) are essential for producing sound, strong keratin.

Pigment retention.

A weakly formed hair structure is less able to receive and hold pigment — contributing to loss of colour, and to overall hair quality [6].

Go deeper

Primary sources

[6]
Daulatabad, D., et al. (2017) — International Journal of TrichologyLinks low B12, folate, and biotin to premature canities.

§ 06.

Oxidative stress.

The original suspect, and a confirmed one. Oxidative stress is cumulative damage from unstable molecules (reactive oxygen species). In hair greying, the primary villain is hydrogen peroxide (H₂O₂).

H₂O₂ byproduct.

A natural byproduct of metabolism. Normally, the enzyme catalase acts as a “mop” and neutralises it on contact.

Catalase decline.

With age, the catalase mops wear out and their levels drop [10].

The double damage.

H₂O₂ builds up. It bleaches the melanin already made, and damages the tyrosinase enzyme — preventing new pigment from forming. An internal bleaching that floods the entire follicle.

Go deeper

Primary sources

[10]
Wood, J. M., et al. (2009) — FASEB JournalThe foundational paper on the H₂O₂ mechanism in senile hair greying.

Bottom line.

Taken together, these six drivers show greying as a sequence of interconnected failures rather than a single event. The pigment stem-cell reserve becomes depleted or dysfunctional; stress can accelerate that loss; pigment inputs and metabolic support become less reliable; structural integrity weakens; and oxidative damage adds further wear across the system.

Naming those six failures — and how they compound — is where any serious response to hair greying has to begin. Everything downstream follows from the resolution of the map.

Single-pathway treatments have struggled because the problem is not single-pathway.

Research is where Hair Labs shows how this map becomes a formulation problem: which drivers must be answered, which compounds survive, and which claims the evidence will not carry.

Read the Research

The map is the starting point, not the end of the argument. The next chapter asks the question that follows from it: once these failures have occurred, how much of the loss is actually fixed — and how much is still open?

№ 02Is hair greying permanent?