Misplaced cells prevent hair regrowth

This hypothesis asks why aging human skin may close wounds yet later struggle to regrow hair: capable cells may be in the wrong place. It rebuilds paired skin samples with the same number of barcoded epithelial cells, cells that form the skin surface and hair follicles, labelled to track origin. One sample moves cells between the epidermis, outer skin, and follicular niches, where hair grows. A sham retains original locations. Both have the same cell roster and matched stroma, support tissue. Hair production after a delayed functional challenge is the deciding readout. Recovery only after reassignment would support misplaced competent cells; persistent impairment after verified engraftment and compatibility would favor impaired repeated division or immune attack.