摘要Aim:This study presents an experimental approach for the long-term(16 years)in vivo observation of deeper structures in human scalp hair follicles,focusing on shortened hair cycles.When hair follicles entered a prolonged dormancy stage(3 years),rapid regrowth of thinning hair was stimulated by the topical application of a drug approved for promoting hair growth.Methods:While intra-epidermal chambers were ineffective as recipient sites,the most superficial dermal implantation proved successful for heterotopic transplantation of single scalp hair follicle grafts,enabling hair growth during successive cycles.Results:The study confirms the known reduction in daily hair growth rates while maintaining hair diameter.Notably,a unique and exceptional"non-correlation"was observed between scalp hair diameter and linear growth rates.While the initial shortening of the hair cycle duration was recorded in the first 3 years post-grafting,a further reduction eventually led to a"dormancy"phase in the long term(16 years post-grafting).Pharmacodynamics revealed that reactivation of hair production,following less than 3 months of topical application of a 5%minoxidil solution,suggested very slow daily growth rates and a substantial reduction in hair diameter.Conclusion:The initial findings suggest that non-invasive methods can be used for real-time structural-functional observation of scalp hair roots,enabling the study of cellular activity and movement during successive phases of the hair cycle,including aging and drug effects.