Why Does Human Hair Turn Gray

Gray hair isn't actually gray. There's no gray pigment anywhere in your body. So where does the color go? Scientists have found at least three ways a hair follicle loses its color: pigment stem cells that get stuck in the wrong place, a buildup of the same chemical found in hair bleach, and a stress signal from your nervous system that burns through the color reserve in days. We also look at the genes that set your graying timetable, the medical clues behind early gray, the Marie Antoinette "white overnight" legend, the plucking myth, and whether gray hair can ever be reversed. CHAPTERS 0:00 Where does the color go? 1:31 Gray hair isn't gray 3:15 Why a hair's color is locked in 4:52 The pigment factory inside your follicle 7:59 The hair cycle and the stem cell savings account 11:20 Stuck stem cells (NYU, 2023) 14:53 Hair that bleaches itself (2009) 18:38 The genes behind graying 22:11 Does stress really turn hair gray? 24:47 Stress and gray hairs that regain color 26:55 Medical clues: B12, thyroid, vitiligo, smoking 29:11 Marie Antoinette and "white overnight" 31:14 Myths: plucking and more 33:16 Can gray hair be reversed? 36:15 So where does the color go? PEOPLE MENTIONED Qi Sun and Mayumi Ito (NYU Langone Health), John M. Wood (University of Bradford), Kaustubh Adhikari and Andrés Ruiz-Linares (University College London), Ya-Chieh Hsu (Harvard University), Martin Picard and Ayelet Rosenberg (Columbia University), Noelia Rivera (dermatologist, Spain), Marie Antoinette, Thomas More SOURCES Background biology (0:00-11:20): Tobin D.J., Paus R. (2001). Graying: gerontobiology of the hair follicle pigmentary unit. Experimental Gerontology. https://doi.org/10.1016/S0531-5565(00... Nishimura E.K. et al. (2005). Mechanisms of hair graying: incomplete melanocyte stem cell maintenance in the niche. Science. https://doi.org/10.1126/science.1099593 (melanocyte stem cells, 9:17) 11:20 Sun Q. et al. (2023). Dedifferentiation maintains melanocyte stem cells in a dynamic niche. Nature. https://doi.org/10.1038/s41586-023-05... 14:59 Wood J.M. et al. (2009). Senile hair graying: H2O2-mediated oxidative stress affects human hair color by blunting methionine sulfoxide repair. The FASEB Journal. https://doi.org/10.1096/fj.08-125435 19:05 Adhikari K. et al. (2016). A genome-wide association scan in admixed Latin Americans identifies loci influencing facial and scalp hair features. Nature Communications. https://doi.org/10.1038/ncomms10815 21:28 Pandhi D., Khanna D. (2013). Premature graying of hair. Indian Journal of Dermatology, Venereology and Leprology. https://doi.org/10.4103/0378-6323.116733 21:47 Panhard S. et al. (2012). Greying of the human hair: a worldwide survey, revisiting the "50" rule of thumb. British Journal of Dermatology. https://doi.org/10.1111/j.1365-2133.2... 22:36 Zhang B. et al. (2020). Hyperactivation of sympathetic nerves drives depletion of melanocyte stem cells. Nature. https://doi.org/10.1038/s41586-020-19... 24:52 Rosenberg A.M. et al. (2021). Quantitative mapping of human hair greying and reversal in relation to life stress. eLife. https://doi.org/10.7554/eLife.67437 28:26 Mosley J.G., Gibbs A.C. (1996). Premature grey hair and hair loss among smokers: a new opportunity for health education? BMJ. https://doi.org/10.1136/bmj.313.7072.... 28:38 Zayed A.A. et al. (2013). Smokers' hair: Does smoking cause premature hair graying? Indian Dermatology Online Journal. https://doi.org/10.4103/2229-5178.110586 34:15 Rivera N. et al. (2017). Hair repigmentation during immunotherapy treatment with an anti-programmed cell death 1 and anti-programmed cell death ligand 1 agent for lung cancer. JAMA Dermatology. https://doi.org/10.1001/jamadermatol.... DISCLAIMER This video is for educational and entertainment purposes only and is not medical advice. It does not diagnose, treat, or recommend any product. If you notice graying very early or alongside other symptoms, talk to a qualified doctor. Several studies discussed were done in mice, and results may not apply to humans. Illustrations were created with the help of AI tools and are simplified cartoons, not accurate anatomy. All studies belong to their respective authors and publishers and are cited here for commentary and education. If questions like this are your thing, like, comment, and subscribe to Unsolved Sketch. #grayhair #science #biology