Viability of Hair Grafts Based upon Environment:
Rob
October 3, 2017 at 3:39 pm
Hey Tom,
It’s a great question. I’m currently in the process of submitting a hypothetical Androgenetic Alopecia pathogenesis model to an academic journal, and answering this question is part of the discussion section — because it’s one of the biggest pieces of evidence that stands against the hypothesis. To quote from the paper:
“Most hair transplant surgeries transplant more than just the hair follicle itself. Follicular unit grafts (FUG) procedures transplant “1–4 terminal hair follicles, one (or rarely two) vellus follicles, associated sebaceous lobules, insertion of erector pili muscle, [and the] perifollicular neurovascular network”… hair transplant donor hair and its surrounding tissues are not likely affected by the same perifollicular fibrosis or dermal sheath thickening observed in Androgenetic Alopecia-affected tissues. Comparably, Androgenetic Alopecia progression often takes decades until completion. If a majority of transplanted donor hairs survive for at least one year after hair transplantation, it’s possible that their supporting hair follicles have not yet had enough time to develop perifollicular fibrosis or dermal sheath thickening, and eventually the onset of hair follicle miniaturization…
“Interestingly, one study comparing hair characteristics of transplanted hairs to and from legs and balding scalps showed that “the recipient site influences the growth characteristics of transplanted hairs”, with “the thickness of the epidermis, dermis, or subcutaneous tissue, blood supply, or other factors play[ing] a role in survival and growth rate differences.” Another study showed that balding human vellus hair regenerates just as well, and sometimes better, on immunodeficient mice versus terminal human hair. This suggests that tissue environment impacts hair follicle growth capabilities, and that the tissue environment in balding scalps may be a limiting factor in Androgenetic Alopecia hair follicle recovery. This is in-line with our hypothetical model, and suggests the need for long-term (decades) studies to determine the true fate of transplanted donor hairs in Androgenetic Alopecia sites.”
The short answer: hair transplants also transplant the tissues around donor hairs, and these tissues are unaffected by fibrosis, which give the hairs that they support a significant cushion window until miniaturization. Since hair loss is often a decades-long process, more studies are needed to determine if transplanted hair follicles really do thin, or if they stay protected forever. From my experience, the majority of readers who’ve gotten a hair transplant and emailed me are emailing me because their transplanted hairs eventually thinned — so there’s also the possibility that donor hair miniaturization is much more common than we think.
Best,
Rob