Interesting article :
Bald scalp in men with androgenetic alopecia retains hair follicle stem cells but lacks CD200-rich and CD34-positive hair follicle progenitor cells. This is exciting because this means that the critical elements for creating the mature hair follicle is in the scalp and once the progenitor cell defect is solved, we should produce gobs of good hair bringing back what was lost.
https://www.jci.org/articles/view/44478