Real-time in vivo structure-function study of scalp hair cycles: an experimental approach for monitoring living hair roots with a 20-year follow-up

Abstract

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.

Keywords

Isolated hair follicle / live observation of hair roots / hair cycle / hair growth / confocal microscopy / in vivo studies / trichoscopy / phototrichogram

References

[1] Nordström REA. Synchronous balding of scalp and hair-bearing grafts of scalp transplanted to the skin of the arm in male pattern baldness. Acta Derm Venereol. 1978;59:266-7. Available from: https://medicaljournalssweden.se/actadv/article/view/17137/20989. [Last accessed on 24 Feb 2025].

[2] Kim JC,Choi YC. Regeneration of the human scalp hair follicle after horizonal sectioning: implications for pluripotent stem cells and melanocyte reservoir. In: Van Neste DJJ, Randall V, Baden H, Ogawa H, Oliver R, Editors. Hair research for the next millenium. Elsevier; 1996. pp. 135-9. Available from: https://scholar.google.com/scholar?cluster=1427582052650609232&hl=zh-CN&as_sdt=0,48. [Last accessed on 28 Feb 2025]

[3] Hwang S,Ryu HS.Does the recipient site influence the hair growth characteristics in hair transplantation?.Dermatol Surg2002;28:795-9

[4] Van Neste D.Exhaustive analysis of scalp hair regression: subjective and objective perception from initial hair loss to severe miniaturisation and drug-induced regrowth.Plast Aesthet Res2021;8:16

[5] Van Neste D, Rushton DH, Westgate GE, Duteil L, Roegies K, Ronsse VV. A segmental approach to scoring hair density from global images: introducing the scalp coverage scoring method for clinical trials and practice.Nat Cell Sci2024;2:59-67

[6] Van Neste D. Cinq questions sur les récentes évolutions dans le domaine des techniques d’imagerie capillaire non invasives. Skin. 2010;13:144-9.

[7] Van Neste D. Natural scalp hair regression in preclinical stages of male androgenetic alopecia and its reversal by finasteride.Skin Pharmacol Physiol2006;19:168-76

[8] Van Neste D. Maintenance of optimised hair growth from viable terminal scalp hair follicles at baseline with oral finasteride in male pattern hair loss and first evidence of a “drug dependency” and a post-finasteride “rebound effect”.Skin Res Technol2019;25:712-9

[9] Van Neste D, Leroy T, Conil S. Exogen hair characterization in human scalp.Skin Res Technol2007;13:436-43

[10] Mlosek RK.Ultrasound image of the skin, apparatus and imaging basics.J Ultrason2013;13:212-21 PMCID:PMC4613587

[11] Denk W,Webb WW.Two-photon laser scanning fluorescence microscopy.Science1990;248:73-6

[12] König K.Multiphoton microscopy in life sciences.J Microsc2000;200:83-104

[13] Konig K.High-resolution multiphoton tomography of human skin with subcellular spatial resolution and picosecond time resolution.J Biomed Opt2003;8:432-9

[14] Leroy T.Contrast enhanced phototrichogram pinpoints scalp hair changes in androgen sensitive areas of male androgenetic alopecia.Skin Res Technol2002;8:106-11

[15] Beerens EG,van der Leun JC.Rapid regeneration of the dermal-epidermal junction after partial separation by vacuum: an electron microscopic study.J Invest Dermatol1975;65:513-21

[16] Lange-Asschenfeldt B,Krüger-Corcoran D.Effects of a topically applied wound ointment on epidermal wound healing studied by in vivo fluorescence laser scanning microscopy analysis.J Biomed Opt2009;14:054001

[17] Park JH,Manonukul K.A practical guide to hair graft placement using the sharp implanter method.Clin Cosmet Investig Dermatol2023;16:1777-85 PMCID:PMC10349607

[18] Messenger AG.Minoxidil: mechanisms of action on hair growth.Br J Dermatol2004;150:186-94

[19] Neste D. Placebo-controlled dose-effect studies with topical minoxidil 2% or 5% in male-patterned hair loss treated with oral finasteride employing an analytical and exhaustive study protocol.Skin Res Technol2020;26:542-57 PMCID:PMC7497182

[20] Tételin C. Linear hair growth rate and diameter of hairs grown in vitro: a relevant correlation. In: Van Neste D, Randall V, Baden H, Ogawa H, Oliver B, Editors. Hair research for the next millenium. Elsevier Scienc, Excerpta Medica, International Congress Series 1111; 1996. pp. 183-6.

[21] Jimenez F, Alam M. The proportion of catagen and telogen hair follicles in occipital scalp of male androgenetic alopecia patients: challenging the established dogma.Exp Dermatol2024;33:e70001

[22] Oh JW,Langan EA.A guide to studying human hair follicle cycling in vivo.J Invest Dermatol2016;136:34-44 PMCID:PMC4785090

[23] Brouwer B, Tételin C, Leroy T, Bonfils A, Van Neste D. A controlled study of the effects of RU58841, a non-steroidal antiandrogen, on human hair production by balding scalp grafts maintained on testosterone-conditioned nude mice.Br J Dermatol1997;137:699-702

[24] Van Neste D, Gillespie RC, Marshall A, Taieb, De Brouwer B. Morphological and biochemical characteristics of trichothiosdystrophy-variant hair are maintained after grafting of scalp specimens on to nude mice.Br J Dermatol1993;128:384-7