Why Hair Goes Grey From Inside the Follicle Outward

Grey hair is not hair that has lost its colour. It is hair that was never given any to begin with. The distinction sounds small, but it changes everything about how greying actually works, and why it cannot be reversed by anything applied to the strand itself.




The colour in your hair is produced by melanocytes, pigment-making cells that sit at the base of each follicle, clustered around the dermal papilla. Each time a new hair strand forms, these cells inject melanin granules directly into the keratinocytes, the cells that build the shaft. The strand grows upward already coloured, like a thread dyed at the source rather than painted at the end.


There are two types of melanin at work. Eumelanin produces brown and black tones. Pheomelanin produces red and yellow. The ratio between them, set by genetics, determines your natural shade. Blonde hair has low eumelanin. Black hair has high eumelanin. Red hair has high pheomelanin. Grey hair has neither, because by the time a grey strand forms, the melanocytes that would have provided the pigment are no longer doing so.



Melanocytes in the follicle are not permanent cells. They are replenished from a reservoir of melanocyte stem cells, called McSCs, that sit in a protected region of the follicle called the bulge. Each time the follicle cycles through a new growth phase, some of these stem cells migrate downward and mature into active melanocytes, ready to pigment the incoming strand.

Greying begins when this replenishment system starts to break down. The McSC pool depletes over time. Some stem cells lose the signals that tell them to migrate and differentiate correctly. Some are lost to the kind of low-level cellular damage that accumulates across decades. As the reservoir shrinks, fewer and fewer mature melanocytes are available at the start of each new growth cycle. The strands that form during those cycles receive less pigment, or none at all.

This is why greying is gradual rather than sudden. It is not that all the melanocytes in a follicle switch off at once. It is that the supply of replacement cells dwindles, and each new cycle has a slightly smaller workforce than the last. A follicle may produce a pigmented strand, then a partially pigmented one, then a white one, depending on how many functional melanocytes were available at the time that particular strand was built.


Once a strand has emerged from the scalp, it is dead tissue. The melanin it carries, or does not carry, was deposited during formation and is fixed. No oil, serum, supplement, or topical treatment can introduce pigment into a strand that has already grown. The colour a hair has when it leaves the follicle is the colour it will have for its entire life on your head.

This is also why the grey-to-coloured gradient sometimes visible near the root of a transitioning strand is not the hair changing colour as it grows. It is the follicle producing a strand with decreasing pigment density along its length, reflecting what the melanocytes were doing, or stopping doing, during that particular growth phase. The gradient is a record of the follicle's output, written in the strand from the inside out.



Genetics sets the broad timeline. When your follicles begin losing their McSC reserves is largely inherited. But several factors appear to move that timeline forward.

Oxidative stress is the most studied. Melanocytes are particularly sensitive to hydrogen peroxide, which the body produces as a natural byproduct of metabolism and which the follicle normally neutralises with an enzyme called catalase. As catalase activity declines with age, hydrogen peroxide accumulates inside the follicle and damages both active melanocytes and the stem cells that replenish them. Chronic psychological stress has been linked to accelerated greying in animal models, with one mechanism involving the rapid depletion of the McSC pool through overstimulation of the nervous system's stress response. Nutritional deficiencies, particularly in vitamin B12, copper, and ferritin, are associated with premature greying in younger people, likely because melanocytes depend on these for the biochemical steps that produce melanin. Smoking is independently associated with earlier onset, though the precise mechanism is still being studied.

None of these factors override genetics. They interact with an inherited baseline. Someone whose follicles were always going to grey early will grey earlier still under chronic stress or a B12 deficiency. Someone whose follicles were set to hold pigment into their sixties may see some acceleration but not a dramatic shift.

The honest answer is: partially, and only at the margins. Addressing a confirmed nutritional deficiency, through a blood test, not assumption, can sometimes pause premature greying in younger people whose McSC loss was being driven by that deficiency rather than by age-related depletion. Correcting a B12 or ferritin deficit is worth doing for reasons well beyond hair, and if it also preserves follicle function, that is a real benefit. Reducing chronic oxidative load through sleep, not smoking, and not chronically under-eating is reasonable advice for the same reason.

What does not work: topical melanin, melanin supplements, onion juice, curry leaves applied to the scalp, or any product that claims to reactivate dormant melanocytes. The follicle's pigment system is not dormant, it has lost the stem cells that would have kept it running. Stimulating the scalp surface does not reach the bulge region where McSC replenishment happens.

Research into actual reversal, restoring the McSC pool or reactivating depleted melanocytes, is active and genuinely interesting. Some early-stage findings suggest that certain cellular signals involved in follicle cycling could influence McSC behaviour. None of this has translated into a usable intervention, and timelines for anything that might are impossible to give honestly.

Greying is one of the few visible signs of ageing that maps almost directly to a specific, well-understood cellular mechanism. The follicle is not failing. It is running out of the raw material it needs to do one particular job. That is a different thing, and knowing the difference is the beginning of not being misled about what can change it.

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