Why Does Hair Turn Grey?

Hair doesn't turn grey — it grows grey. Every strand leaves the follicle completely white, and the colour you see is actively added during growth. So greying isn't a fade. It's a failure of the system that was colouring your hair all along. In this episode, Jen, Chris, and Jamie unpack exactly what's happening beneath the surface. A landmark study published in Nature revealed that the stem cells responsible for hair colour don't die — they get physically stuck in the wrong part of the follicle and never receive the signal to produce pigment. There's also a second mechanism at work: hydrogen peroxide builds up inside the follicle as the enzyme that neutralises it declines, bleaching the hair from the inside out. Research from the University of Bradford confirmed that grey hair samples contain high levels of hydrogen peroxide while pigmented hair has none. The episode also covers the 2020 Harvard study linking stress to accelerated greying via the fight-or-flight system, the genetics research that identified the first gene specifically associated with greying, the ethnic patterns that affect timing, and the nutritional deficiencies — particularly B12 and copper — that are often overlooked as a cause of premature greying. And with recent research suggesting those stuck stem cells may be persuadable, the question of reversal is less far-fetched than it once seemed. Timestamps 00:00 - Why does hair turn grey? 01:03 - Hair grows grey, not turns grey 01:47 - The cells that colour your hair 02:32 - The stem cell discovery explained 03:56 - Hydrogen peroxide and internal bleaching 05:07 - Stress, genetics and the greying timeline 07:11 - Nutrition, reversal and what comes next Resources Mentioned 📌 Nature — melanocyte stem cell mobility study: https://www.nature.com/articles/s4158... 📌 University of Bradford — hydrogen peroxide and grey hair research: https://bradscholars.brad.ac.uk/entit... 📌 Harvard University — stress and greying mechanism study (2020): https://www.hsci.harvard.edu/news/sol... Connect & Continue Learning 🔔 Subscribe for weekly science-backed answers: ‪@sothatswhypodcast‬ 💬 When did you find your first grey hair — and how did you react? Tell us below. #SoThatsWhy #GreyHair #HairScience #HealthScience #SciencePodcast