The Science of Hair Aging: Why Hair Turns Gray, Thin, and Fragile
Understanding the fundamentals is critical as hair restoration treatment options expand.
KEY TAKEAWAYS
- Hair aging is driven by complex biological changes—including mitochondrial dysfunction, oxidative stress, stem cell depletion, and shortened hair growth cycles—that contribute to graying, thinning, and increased fragility.
- Emerging evidence suggests systemic stressors such as COVID-19 infection, menopause, rapid weight loss, and GLP-1 receptor agonist use may accelerate hair shedding through metabolic stress and disruption of normal follicular function.
- New therapeutic strategies are shifting beyond traditional hair-loss treatments toward approaches that target mitochondrial health, oxidative balance, and regenerative pathways to support healthier follicular aging.
Hair aging is often one of the most apparent and emotionally striking indicators of the aging process. The earliest visible signs of biological aging include emerging silver strands, diminished density, increased shedding, and altered texture. These changes reflect more than cosmetic transformation. They represent shifts in follicular cycling, pigmentation, stem cell activity, oxidative stress, and cellular energy production.1,2
Hair aging and hair loss are becoming more common concerns in clinical practice. Many patients report sudden shedding, reduced density, altered texture, or accelerated thinning after systemic stressors such as COVID-19 infection, rapid weight loss, menopause, nutritional changes, or medication-related metabolic shifts. Telogen effluvium has been increasingly reported after COVID-19 infection, and emerging evidence suggests that GLP-1 receptor agonists (GLP-1 RA) associated with rapid weight loss may also contribute to shedding through metabolic stress and nutritional deficiencies.3,4
Hair follicles require a steady supply of energy to function properly. They depend on mitochondrial oxidative phosphorylation to activate stem cells, support keratinocyte growth, maintain pigmentation, and regulate normal hair cycling. Researchers now believe mitochondrial dysfunction is a central mechanism in hair aging. Dysfunctional mitochondria produce less ATP and more reactive oxygen species (ROS), increasing oxidative stress and promoting cellular senescence within the aging follicle.5,6,7
Hair follicles undergo a cyclical process consisting of anagen (growth), catagen (regression), telogen (rest), and exogen (shedding). With aging, the anagen phase shortens while the telogen phase lengthens, resulting in diminished density and slower follicular renewal.8 Follicular miniaturization also occurs, where thicker terminal hairs are gradually replaced by finer, weaker hairs.9,10
Table generated by ChatGPT based on data cited in the article.
Oxidative stress plays a major role in pigment loss and graying. Reactive oxygen species, particularly hydrogen peroxide (H₂O₂), accumulate in aging follicles and disrupt melanin production by damaging key enzymes involved in pigmentation.11,12 Catalase levels also decline with age, reducing the follicle’s ability to neutralize oxidative damage.13 Graying is associated with the depletion and dysfunction of melanocyte stem cells, resulting in less melanin transfer to the hair shaft.11,14 Psychological stress may accelerate this process through sympathetic nervous system activation and depletion of melanocyte stem cells.15 Stem cell exhaustion and telomere shortening further contribute to hair aging. Hair follicle stem cells and melanocyte stem cells accumulate DNA damage over time, reducing their ability to regenerate healthy hair and maintain pigmentation.16,17,18 Structural aging also affects the hair shaft itself, leading to finer, drier, rougher, and more fragile hair due to decreased keratin synthesis and reduced sebum production.13,19,20
Traditional therapies such as minoxidil, platelet-rich plasma (PRP), and low-level light therapy (LLLT) aim to improve follicular signaling and prolong the anagen phase. Emerging therapies are increasingly focused on mitochondrial function, oxidative stress reduction, and stem cell support.5,7,21 Photobiomodulation with red and near-infrared light may improve mitochondrial activity and ATP production, while regenerative compounds such as GHK-Cu are being studied for their antioxidant and tissue-repair effects.21-24 As the science of hair aging continues to evolve, visible changes in the hair are increasingly understood as signs of deeper biological changes involving stem cell function, oxidative balance, cellular metabolism, and regenerative decline within the follicle.1,2,15,25
1. Liang A, et al. Signaling pathways in hair aging. Front Cell Dev Biol. 2023;11. doi:10.3389/fcell.2023.1278278.
2. Adav SS, Ng KW. Recent omics advances in hair aging biology and hair biomarkers analysis. Ageing Res Rev. 2023;91:102041. doi:10.1016/S1568-1637(23)00200-3.
3. Patel S, Colavincenzo M. Greater susceptibility to telogen effluvium in the setting of severe COVID-19 infection: findings from a retrospective cohort study. Arch Dermatol Res. 2026;318:52. doi:10.1007/s00403-025-04490-7.
4. Gupta AK, Teasell EM, Economopoulos V, Mirmirani P. GLP-1 therapies and hair loss: A systematic review of current evidence and implications for counseling. Sci Prog. 2026;109(2). doi:10.1177/00368504261444578.
5. Dong T, Li Y, Jin S, et al. Progress on mitochondria and hair follicle development in androgenetic alopecia: relationships and therapeutic perspectives. Stem Cell Res Ther. 2025;16(1). doi:10.1186/s13287-025-04182-z.
6. Feichtinger RG, Sperl W, Bauer JW, Kofler B. Mitochondrial dysfunction: a neglected component of skin diseases. Exp Dermatol. 2014;23(9):607-614. doi:10.1111/exd.12484.
7. Wang D, Jiang J, Wang M, et al. Mitophagy promotes hair regeneration by activating glutathione metabolism. Research. 2024;7. doi:10.34133/research.0433.
8. Courtois M, Loussouarn G, Hourseau C, Grollier JF. Ageing and hair cycles. Br J Dermatol. 1995;132(1):86-93. doi:10.1111/j.1365-2133.1995.tb08630.x.
9. Williams R, Pawlus AD, Thornton MJ. Getting under the skin of hair aging: the impact of the hair follicle environment. Exp Dermatol. 2020;29(7):588-597. doi:10.1111/exd.14109.
10. Fernandez-Flores A, Saeb-Lima M, Cassarino DS. Histopathology of aging of the hair follicle. J Cutan Pathol. 2019;46(7):508-519. doi:10.1111/cup.13467.
11. Sun Q, Lee W, Hu H, et al. Dedifferentiation maintains melanocyte stem cells in a dynamic niche. Nature. 2023;616:774-782. doi:10.1038/s41586-023-05960-6.
12. Wood JM, et al. Senile hair graying: H2O2-mediated oxidative stress affects human hair color by blunting methionine sulfoxide repair. FASEB J. 2009;23(7):2065-2075. doi:10.1096/fj.08-125435.
13. Monselise A, Cohen DE, Wanser R, Shapiro J. What ages hair? Int J Womens Dermatol. 2017;3(1 Suppl):S52-S57. doi:10.1016/j.ijwd.2017.02.010.
14. Matsumura H, et al. Hair follicle aging is driven by transepidermal elimination of stem cells via COL17A1 proteolysis. Science. 2016;351(6273):aad4395. doi:10.1126/science.aad4395.
15. Zhang B, et al. Hyperactivation of sympathetic nerves drives depletion of melanocyte stem cells. Nature. 2020;577(7792):676-681. doi:10.1038/s41586-020-1935-3.
16. Williams RS, Westgate GE, Pawlus AD, Sikkink SK, Thornton MJ. Age-related changes in female scalp dermal sheath and dermal fibroblasts: how the hair follicle environment impacts hair ageing. J Invest Dermatol. 2020;141(suppl 1). doi:10.1016/j.jid.2020.11.009.
17. Keyes BE, Segal JP, Heller E, et al. Nfatc1 orchestrates aging in hair follicle stem cells. Proc Natl Acad Sci U S A. 2013;110(51):E4950-E4959. doi:10.1073/pnas.1320301110.
18. Ji J, et al. Aging in hair follicle stem cells and niche microenvironment. J Dermatol. 2017;44(10):1097-1104. doi:10.1111/1346-8138.13897.
19. Trüeb RM. Aging of hair. J Cosmet Dermatol. 2005;4(1):60-72. doi:10.1111/j.1473-2165.2005.40203.x.
20. Baltenneck F, Genty G, Bou Samra E, et al. Age-associated thin hair displays molecular, structural and mechanical characteristic changes. J Struct Biol. 2022;214(4):107908. doi:10.1016/j.jsb.2022.107908.
21. Avci P, Gupta GK, Clark J, Wikonkal N, Hamblin MR. Low-level laser (light) therapy (LLLT) for treatment of hair loss. Lasers Surg Med. 2014;46(2):144-151. doi:10.1002/lsm.22170.
22. Chung H, Dai T, Sharma SK, Huang YY, Carroll JD, Hamblin MR. The nuts and bolts of low-level laser (light) therapy. Ann Biomed Eng. 2012;40(2):516-533. doi:10.1007/s10439-011-0454-7.
23. Pickart L, Margolina A. Regenerative and protective actions of the GHK-Cu peptide in the light of the new gene data. Int J Mol Sci. 2018;19(7):1987. doi:10.3390/ijms19071987.
24. Pickart L. The human tri-peptide GHK and tissue remodeling. J Biomater Sci Polym Ed. 2008;19(8):969-988. doi:10.1163/156856208784909435.
25. Jang H, Jo Y, Lee JH, Choi S. Aging of hair follicle stem cells and their niches. BMB Rep. 2023;56(1):2-9. doi:10.5483/BMBRep.2022-0183.
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