TLDR Hedgehog signaling helps keep hair follicle stem cells the same in both young and old human skin.
The study, involving scalp biopsies from 15 young individuals (below 40 years) and 13 aged individuals (above 70 years), examined the effects of aging on hair follicle stem cells (HFSCs) in human skin. Researchers found no significant differences in hair follicle density, bulge cell numbers, or the expression of HFSC markers such as KRT15, KRT19, and various others between young and aged individuals. Additionally, the study demonstrated that Hedgehog (Hh) signaling, which was activated in human bulge cells and down-regulated in differentiated hair follicle keratinocytes, plays a role in maintaining the bulge cell phenotype in both young and aged skin. Activation of Hh signaling through overexpression of the transcription factor Gli1 induced the transcription of HFSC markers in cultured keratinocytes, suggesting that Hh signaling is crucial for maintaining HFSC characteristics regardless of age.
835 citations,
October 2008 in “Nature Genetics” Lgr5 is a marker for active, long-lasting stem cells in mouse hair follicles.
143 citations,
September 2008 in “Experimental gerontology” Skin aging is due to impaired stem cell mobilization or fewer responsive stem cells.
190 citations,
July 2006 in “Experimental Dermatology” 
224 citations,
March 2006 in “Seminars in Cutaneous Medicine and Surgery” The document concludes that understanding hair follicle biology can lead to better hair loss treatments.
550 citations,
December 2005 in “The Journal of clinical investigation/The journal of clinical investigation” Researchers successfully isolated and identified key markers of stem cell-enriched human hair follicle bulge cells.
291 citations,
October 2005 in “Proceedings of the National Academy of Sciences of the United States of America” Adult stem cells from rat whisker follicles can regenerate hair follicles and sebaceous glands.
4 citations,
August 2005 in “Archives of Dermatological Research” Higher p63 and CD34 levels found in specific scalp areas may affect hair loss progression.
May 2023 in “Frontiers in Cell and Developmental Biology” The document concludes that using stem cells to regenerate hair follicles could be a promising treatment for hair loss, but there are still challenges to overcome before it can be used clinically.
7 citations,
February 2022 in “Stem cell reviews and reports” Skin cells show flexibility in healing wounds and forming tumors, with potential for treating hair disorders and chronic ulcers.
35 citations,
February 2019 in “Cell Communication and Signaling” BMP6 and Wnt10b control whether hair follicles are resting or growing.
2 citations,
November 2022 in “Oxidative Medicine and Cellular Longevity” Exosomes from dermal papilla cells help hair follicle stem cells grow and survive.
14 citations,
February 2014 in “Experimental Cell Research” The conclusion is that teeth, hair, and claws have similar stem cell niches, which are important for growth and repair, and more research is needed on their regulation and potential markers.
