Mechanical epilation exerts complex biological effects on human hair follicles and perifollicular skin: An ex vivo study approach

ObjectiveElectrical epilation of unwanted hair is a widely used hair removal method, but it is largely unknown how this affects the biology of human hair follicles (HF) and perifollicular skin. Here, we have begun to explore how mechanical epilation changes selected key biological read-out parameters ex vivo within and around the pilosebaceous unit.MethodsHuman full-thickness scalp skin samples were epilated ex vivo using an electro-mechanical device, organ-cultured for up to 6 days in serum-free, supplemented medium, and assessed at different time points by quantitative (immuno-)histomorphometry for selected relevant read-out parameters in epilated and sham-epilated control samples.ResultsEpilation removed most of the hair shafts, often together with fragments of the outer and inner root sheath and hair matrix. This was associated with persistent focal thinning of the HF basal membrane, decreased melanin content of the residual HF epithelium, and increased HF keratinocyte apoptosis, including in the bulge, yet without affecting the number of cytokeratin 15+ HF epithelial stem cells. Sebocyte apoptosis in the peripheral zone was increased, albeit without visibly altering sebum production. Epilation transiently perturbed HF immune privilege, and increased the expression of ICAM-1 in the bulge and bulb mesenchyme, and the number of perifollicular MHC class II+ cells as well as mast cells around the distal epithelium and promoted mast cell degranulation around the suprabulbar and bulbar area. Moreover, compared to controls, several key players of neurogenic skin inflammation, itch, and/or thermosensation (TRPV1, TRPA1, NGF, and NKR1) were differentially expressed in post-epilation skin.ConclusionThese data generated in denervated, organ-cultured human scalp skin demonstrate that epilation-induced mechanical HF trauma elicits surprisingly complex biological responses. These may contribute to the delayed re-growth of thinner and lighter hair shafts post-epilation and temporary post-epilation discomfort. Our findings also provide pointers regarding the development of topically applicable agents that minimize undesirable sequelae of epilation. ObjectifL'epilation electrique des poils indesirables est une methode d'epilation largement utilisee, mais on ne connait pas l'ampleur de son effet sur la biologie des follicules pileux humains (FP) et de la peau perifolliculaire. Dans cette etude, nous avons commence a explorer comment l'epilation mecanique modifie certains parametres de mesures biologiques cles ex vivo a l'interieur et autour de l'unite pilo-sebacee.Des echantillons de peau du cuir chevelu humain de pleine epaisseur ont ete epiles ex vivo a l'aide d'un dispositif electromecanique, cultives biologiquement pendant un maximum de 6 jours dans un milieu complet sans serum, et evalues a differents moments par (immuno-)histomorphometrie quantitative pour certains parametres de mesures pertinents dans des echantillons avec epilation et des echantillons temoins avec epilation simulee.ResultatsL'epilation a enleve la plupart des poils, souvent avec des fragments de la gaine de la racine externe et de la matrice pileuse. Cela a ete associe a un amincissement focal persistant de la membrane basale du FP, a une diminution de la teneur en melanine de l'epithelium residuel du FP et a une augmentation de l'apoptose des keratinocytes du FP, y compris dans la surface arrondie, mais sans affecter le nombre de cellules souches epitheliales du FP positives pour la cytokeratine 15. L'apoptose des sebocytes de la zone peripherique etait augmentee, sans pour autant alterer visiblement la production de sebum. L'epilation a temporairement perturbe l'immunoprivilege du FP et a augmente l'expression de l'ICAM-1 dans la surface arrondie et le mesenchyme du bulbe, ainsi que le nombre de cellules perifolliculaires du CMH de classe II et des mastocytes autour de l'epithelium distal, et a favorise la degranulation des mastocytes autour de la zone supra-bulbaire et bulbaire. En outre, par rapport aux echantillons temoins, plusieurs acteurs cles de l'inflammation neurogene cutanee, de la demangeaison et/ou de la thermosensation (TRPV1, TRPA1, NGF et NKR1) ont ete exprimes de maniere differentielle dans la peau apres l'epilation.Ces donnees generees dans la peau du cuir chevelu humain denervee et cultivee biologiquement demontrent que le traumatisme du FP induit par l'epilation mecanique provoque des reponses biologiques etonnamment complexes. Celles-ci peuvent contribuer a retarder la repousse des poils plus fins et plus clairs apres l'epilation, et a provoquer une gene temporaire apres l'epilation. Nos resultats fournissent egalement des pistes concernant le developpement d'agents applicables par voie topique qui minimisent les sequelles indesirables de l'epilation. Human hair follicles experience epilation-induced mechanical trauma that elicits complex biological responses, which might contribute both to the delayed re-growth of thinner and lighter hair shafts post-epilation and to temporary post-epilation discomfort.image