That is a good point, but I'm still not sure how wounding would be able to undo the irreversible changes that take place. Research shows that over time, miniaturized hairs lose contact with the Arrector Pili muscle, and once this contact has been lost, hair loss is irreversible. Also, bald scalps in men with Androgenetic Alopecia retain hair follicle stem cells, but have lost the progenitor cells that are believed to be necessary for hair growth.
Here are a few studies:
This one from 2012:
Miniaturized Hairs Maintain Contact with the Arrector Pili Muscle in Alopecia Areata but not in Androgenetic Alopecia: A Model for Reversible Miniaturization and Potential for Hair Regrowth
"Contact between the APM and the bulge in AA may be required for reversal of hair follicle miniaturization. Maintenance of contact between miniaturized follicles in AA could explain the complete hair regrowth while loss of contact between the APM and the bulge in MPHL and FPHL may explain why the hair loss is largely irreversible. This loss of contact may reflect changes in stem cell biology that also underlie irreversible miniaturization."
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Three-dimensional reconstructions of AA (a) and FPHL (b) demonstrating the loss of contact of the APM with the ORS of the vellus hair follicle in FPHL which is largely irreversible compared with maintenance of this contact of the APM with ORS in AA which is potentially completely reversible
And a second study from 2014:
Destruction of the arrector pili muscle and fat infiltration in androgenic alopecia.
"Hair loss is caused by follicle miniaturization, which is largely irreversible beyond a certain degree of follicular regression."
"APM degeneration and replacement with fat in Androgenetic Alopecia has not previously been described. The underlying mechanism remains to be determined. However, we speculate that this phenomenon might be related to depletion of stem or progenitor cells from the follicle mesenchyme, explaining why Androgenetic Alopecia is treatment resistant."
And another study from 2011:
Bald Scalp in Men With Androgenetic Alopecia Retains Hair Follicle Stem Cells but Lacks CD200-rich and CD34-positive Hair Follicle Progenitor Cells
"Androgenetic alopecia (Androgenetic Alopecia), also known as common baldness, is characterized by a marked decrease in hair follicle size, which could be related to the loss of hair follicle stem or progenitor cells. To test this hypothesis, we analyzed bald and non-bald scalp from Androgenetic Alopecia individuals for the presence of hair follicle stem and progenitor cells. Cells expressing cytokeratin15 (KRT15), CD200, CD34, and integrin, α6 (ITGA6) were quantitated via flow cytometry. High levels of KRT15 expression correlated with stem cell properties of small cell size and quiescence. These KRT15(hi) stem cells were maintained in bald scalp samples. However, CD200(hi)ITGA6(hi) and CD34(hi) cell populations--which both possessed a progenitor phenotype, in that they localized closely to the stem cell-rich bulge area but were larger and more proliferative than the KRT15(hi) stem cells--were markedly diminished. In functional assays, analogous CD200(hi)Itga6(hi) cells from murine hair follicles were multipotent and generated new hair follicles in skin reconstitution assays. These findings support the notion that a defect in conversion of hair follicle stem cells to progenitor cells plays a role in the pathogenesis of Androgenetic Alopecia."