Hair turns grey or white when pigment-producing cells in the follicle stop supplying enough melanin to new hair shafts.
Where hair colour comes from
Hair itself is made mainly of keratin. Its colour is added while a new strand grows inside the follicle. Melanocytes produce pigments called melanins and transfer them into the growing hair shaft. Different amounts and types of melanin create black, brown, blond and red shades.
Why colour fades with age
Hair follicles rely on melanocyte stem cells to renew pigment-producing cells. With age, these stem cells can become depleted, damaged or unable to move and mature properly. A new strand then receives less pigment and appears grey; with very little pigment, it appears white.
Genetics, stress and nutrition
Genes strongly influence when greying begins. Research in animals shows severe stress can affect melanocyte stem cells, but one stressful day does not instantly bleach an existing strand. Vitamin B12, iron, thyroid or other medical problems may be associated with premature greying in some people, so sudden early changes should be discussed with a clinician rather than self-treated with supplements.
Can white hair be reversed?
For ordinary age-related greying, there is no established treatment that reliably restores every follicle's pigment. Correcting a diagnosed deficiency may help the underlying health problem, but cosmetic dye remains the predictable way to change visible colour. Claims of guaranteed reversal deserve caution.
Concept Map
Fast facts
| Pigment | Melanin. |
| Pigment cells | Melanocytes inside hair follicles. |
| Major timing factor | Genetics, together with ageing. |
| Medical note | Premature or sudden greying can be discussed with a qualified clinician. |
| Sources | NIH stress and grey-hair research and Nature melanocyte stem-cell study |
Did you know?
An existing strand does not usually lose pigment from tip to root overnight; the visible change mainly appears as newly grown hair emerges with less pigment.
Watch the short here: open the YouTube explanation.
Key takeaway
The chain is follicle -> melanocyte stem cell -> melanocyte -> melanin -> hair colour. Ageing and genetics can interrupt that chain, producing grey or white growth.
