Split-leg comparison of low fluence diode laser and high fluence intense pulsed light in permanent hair reduction in skin types III to IV

Background/Objectives: All the standard light‐based techniques for permanent hair reduction, like laser and intense pulsed light (IPL) employ the highest tolerable fluence with a single pass. As opposed to standard techniques, a new diode laser technique employs low fluence with multiple passes. Here we evaluate and compare the efficacy, treatment time, comfort and safety of the low fluence multiple pass diode laser with high fluence single pass IPL for permanent hair reduction in Type III to IV Asian patients. Methods: Thirty Asian patients with Type III to IV black hair were enrolled and received three sessions of treatments at 6‐weekly to 8‐weekly intervals. A split‐leg study was performed in which the IPL was applied to one leg of each patient while the laser was applied to the other. The patients were followed up for 12 months. Results: All patients were satisfied with the results of the long‐term hair reduction without long‐term side effects. There was no statistically significant difference in hair reduction and treatment time between the laser (76.85%, 21.39 min) and the IPL (74.53%, 22.17 min) (P > 0.05). The visual analogue scale (VAS) pain score of the IPL (5.96) was higher than that of the laser (3.10) (P < 0.01). Conclusions: A series of high fluence single pass IPL and low fluence multiple pass diode laser treatments were performed with similar efficacy, speed and safety for permanent hair reduction. However, low fluence multiple pass diode laser treatment was less painful than high fluence single pass IPL.     

Leptin of dermal adipose tissue is differentially expressed during the hair cycle and contributes to adipocyte‐mediated growth inhibition of anagen‐phase vibrissa hair

Adipose tissue encircles the lower portion of anagen hair follicles and may regulate hair cycle progression. As leptin is a major adipokine, its level of expression from the dermal white adipose tissue during hair cycle progression was studied. The result shows that leptin level is differentially expressed during hair cycle, the lowest in early anagen phase, upregulated in late anagen phase and the highest in the telogen phase. On the other hand, leptin receptor is detected in keratin 15‐positive hair bulge epithelium of both anagen‐ and telogen‐phase hair follicles of mice pelage and vibrissa hair, and hair from human scalp. Leptin contributes to adipocyte‐mediated growth inhibition of anagen‐phase vibrissa hair as demonstrated in organ culture and coculture system. Our data suggest that leptin of dermal white adipose tissue might regulate hair growth and, therefore, hair cycle progression via leptin receptor on the hair follicle epithelium.     

Anagen hair follicle repair: Timely regenerative attempts from plastic extra‐bulge epithelial cells

Anagen hair follicle repair (AHFR) is the regenerative scheme activated to restore the structure and hair growth following injuries to anagen hair follicles. Compared with telogen‐to‐anagen regeneration and hair follicle neogenesis, AHFR is a clinically important, yet relatively unexplored regenerative feature of hair follicles. Due to their highly proliferative character, germinative cells and matrix cells within hair bulbs are highly susceptible to injuries, such as chemotherapy and radiotherapy. Clinical and experimental observations suggest that damaged anagen hair follicles are able to repair themselves to resume anagen growth, bypassing premature catagen/telogen entry. Mechanistically, extra‐bulge epithelial cells in the outer root sheath and the lower proximal cup are quickly mobilized for regeneration. These cells acquire stem cell‐like properties, exhibiting high plasticity by breaking lineage restriction to regenerate all cell types in the lower segment of anagen hair follicles. Facilitating extra‐bulge epithelial cells’ mobilization ameliorates hair loss from chemo‐ and radiotherapy. On the other hand, quiescent bulge stem cells can also be activated, but only after more severe injuries and with slower activation dynamics. They show limited plasticity and regenerate part of the outer root sheath only. The dysrhythmic activation might render bulge stem cells susceptible to concomitant injuries due to their exit from quiescence.     

Expression of the L-fucose moiety on infrainfundibular follicular keratinocytes of terminal follicles, its decreased expression on vellus and indeterminate follicles of androgenetic alopecia, and re-expression in drug-induced hair regrowth.

The distribution of various glycoprotein molecules on the surface of follicular keratinocytes was studied with a panel of lectins with specificity for various sugar moieties on biopsy specimens from both bald/balding scalp and normal occipital scalp, of 23 patients with androgenetic alopecia as well as on biopsies of normal forearm skin of four patients. The most significant differences between bald and normal scalp biopsy were noted with Ulex europaeus agglutinin I (UEA I). We noted an increased (91.8% +/- 3.1; mean +/- SE) expression of UEA I binding sites on the infra-infundibular follicular keratinocytes in anagen terminal scalp hairs, compared to 28.5% +/- 5.2 in the indeterminate (anagen) hairs of balding scalps, and 23.2% +/- 6.3 in the anagen follicles of vellus fore-arm hairs. By contrast, the telogen hairs demonstrated minimal UEA I staining: 4.0% +/- 0.8, mean +/- SE in telogen scalp hairs, 1.8% +/- 0.5 in telogen hairs of balding scalps (0% in completely bald scalps, in which all the hairs were in the telogen phase), and 1.9% +/- 0.2 in telogen forearm hairs. The percentage of UEA I staining correlated with the length of the infra-infundibular follicles in all cases studied. In three cases of hair regrowth after hair growth promotors, the UEA I staining increased to 80.6% +/- 6.1 in anagen hairs and correlated with increased length of infra-infundibular follicles. Our data indicate that there are 1) marked differences between anagen and telogen follicles in UEA I binding to infra-infundibular follicular keratinocytes; 2) the percentage of UEA I staining reflects the size (length) of the infra-infundibular hair follicle; and 3) the anagen follicles of balding scalps (indeterminate hairs) show UEA I staining resembling that exhibited by anagen follicles of vellus hairs.     

Expression of Ras homologous B protein in the human scalp skin and hair follicles: hair follicle cycle stages‐associated changes

Background: RhoB belongs to the Ras homologous (Rho) subfamily which consists of low molecular weight mass GTP‐binding proteins. Rho proteins are regulatory molecules that mediate changes in cell shape, contractility, motility and gene expression. Aim: To test the hypothesis that ‘RhoB protein is expressed in the human skin and its expression undergoes hair follicle cycle dependent changes'. To test this hypothesis, we examined the expression of RhoB in the normal human skin and hair follicles (HFs) using immunohistochemical methods. Methods: A total of 50 normal human scalp skin specimens were obtained from 50 females (age: 53–57 years) undergoing elective cosmetic plastic surgery. The specimens were obtained from both frontal and temporal regions of the scalp. A total of 50 HF, (35 anagen, 10 catagen and 5 telogen) were examined in each case using immunohistologic staining methods. Semiquantitative analysis was done. Results: RhoB protein was strongly expressed in the various elements of the human scalp skin and hair follicles. In the epidermis, a moderate RhoB immunoreactivity was found in all layers except stratum corneum where RhoB protein was completely absent. In sebaceous glands, a strong RhoB immunoreactivity was detected in all sebaceocytes. In the hair follicles, the expression of RhoB protein showed hair follicle cycle stages‐associated changes, i.e. strong expression during anagen, but weak and completely absent expressions during catagen and telogen phases, respectively. Semiquantitative analysis revealed statistically significant high expression values (staining intensity, percentage of positive cells and immunoreactivity scores) in the anagen VI hair follicles compared to either cantagen or telogen ones (p < 0.05). Similarly, RhoB protein expression was significantly high in the stratum basale, stratum spinosum and sebaceous glands compared to stratum granulosum (p < 0.05). Conclusions: Here we report, for the first time, the distribution of RhoB protein in the human scalp skin and hair follicles. We also provide the first indication that there are variations in the expression of this protein in the different stages of the hair cycle. Adly M.A, Assaf H.A, Hussein M.R.A. Expression of Ras homologous B protein in the human scalp skin and hair follicles: hair follicle cycle stages‐associated changes     

Pretreatment of epidermal growth factor promotes primary hair recovery via the dystrophic anagen pathway after chemotherapy‐induced alopecia

Epidermal growth factor (EGF) is not only a cell growth stimulant but also has a catagen‐inducing effect. Because chemotherapeutic agents primarily damage anagen hair follicles, it would be important to investigate whether catagen inducers have beneficial effects in chemotherapy‐induced alopecia (CIA). We pretreated hair follicles with topical EGF‐liposomal solution in the C57BL/6 mouse model of cyclophosphamide‐induced alopecia and observed the catagen‐inducing property and damage response pathway after CIA. We confirmed that topical EGF application induced a catagen‐like stage and found that these catagen‐like hairs were protected from chemotherapy‐mediated damage. Moreover, our results showed that EGF treatment favoured primary hair recovery via the dystrophic anagen pathway after CIA. Given that hair follicles subjected to less severe chemotherapeutic insult enter the dystrophic anagen pathway followed by primary recovery, the results of this study suggest that catagen inducers could be useful as a new alopecia‐protection strategy, especially in the context of CIA.     

HMB-45抗原在毛囊黑素细胞中的表达

用单克隆抗体ＨＭＢ－４５，以ＡＰＡＡＰ法对２０份头皮活检标本的９８个毛囊组织进行染色。其中２０个毛囊为生长早期，６３个为成熟生长期，７个为退行期和８个是休止期。结果，５２个成熟生长期及２０个生长早期毛囊的黑素细胞与单克隆抗体ＨＭＢ－４５显著结合。所有退行期、休止期及工１１个成熟生长期毛囊未被染色。结果提示；ＨＭＢ－４５在毛囊中的表达随毛发生过周期而变化，且与黑素细胞功能活性状态有关。     

Photoepilation with a diode laser vs. intense pulsed light: a randomized,intrapatient left‐to‐right trial

Background Safe and efficient options for removing unwanted hair are in great demand. Laser devices and intense pulsed light (IPL) sources are the most commonly used treatment modalities. Yet, only a few randomized controlled trials (RCTs) comparing laser and IPL devices are available, and RCTs with long‐term results are missing from the literature. Objectives To compare the safety and long‐term efficacy of diode lasers (DL) and IPL sources for axillary hair removal, we conducted an intrapatient, left‐to‐right, assessor‐blinded and controlled trial. Methods IPL (Ellipse Flex PPT; Danish Dermatological Development, Hoersholm, Denmark; λ_em = 600–950 nm) and DL (LightSheer XC system; Lumenis Inc., Santa Clara, CA, U.S.A.; λ_em = 800 nm) treatments were evaluated in 30 study participants (skin type II–III) with unwanted axillary hair growth. Six treatments with each device were carried out at 4‐week intervals. Final assessment was conducted 12 months after the last treatment by means of hair counts using close‐up photographs. The primary endpoint was reduction in hair growth, analysed on an intention‐to‐treat and last‐observation‐carried‐forward basis (n = 30), and secondary endpoints were patient‐rated efficacy, treatment‐related pain, adverse effects and treatment duration. Results Both devices significantly reduced hair counts. Mean reductions from baseline (3 and 12 months after the last treatment) were 59·7% and 69·2% for DL and 42·4% and 52·7% for IPL treatment (P < 0·01), respectively. DL treatment induced significantly more pain [3·7 ± 2·1 (DL) vs. 1·6 ± 1·4 (IPL); P < 0·01; visual analogue scale] but could be conducted faster [33·1 ± 3·8 s (DL) vs. 40·1 ± 5·0 s (IPL); P < 0·01]. No severe side‐effects were observed for either therapy. Conclusions Both DL and IPL treatments are highly effective, long lasting and safe. DL was found to be more effective than IPL treatment. DL treatment was more painful but less time‐consuming than IPL therapy.     

A liposome‐based formulation containing equol,dihomo‐γ‐linolenic acid and propionyl‐l‐carnitine to prevent and treat hair loss: A prospective investigation

Hair loss is a common aesthetic disorder that can be triggered by genetic, inflammatory, hormonal, and environmental factors acting on hair follicles and their life cycle. There are several types of hair loss that differ in causes, symptoms, and spatial and temporal progression. Androgenic alopecia, a common form of hair loss, is the consequence of a decreased microcirculation of the scalp as well as the toxic action of elevated dihydrotestosterone levels on the hair bulbs. In the present study, the lotions TRINOV Lozione Anticaduta Uomo and TRINOV Lozione Anticaduta Donna, containing dihomo‐γ‐linolenic acid (DGLA), S‐equol, and propionyl‐l ‐carnitine, were tested on 30 men and 30 women (mean age of men was 46.6 ± 6.4 years; mean age of women was 49.5 ± 9.0) with signs of androgenic alopecia, respectively. DGLA is a precursor of the prostaglandin PGE1, which acts by improving microcirculation; S‐equol inhibits 5α‐reductases, thus preventing the transformation of testosterone into dihydrotestosterone; and propionyl‐l ‐carnitine promotes lipid metabolism, stimulating energy production. These three molecules are loaded into liposomes for their effective transdermal delivery. Daily topical applications of the lotions resulted in a hair count that significantly increased for women and marginally increased for men after 6 months of treatment. Furthermore, significant increase in anagen hair and a significant decrease in telogen hair were observed starting from 3 months in male and 1 month in female patients. Thus, the formulations under investigation were effective in attenuating androgenic alopecia‐related hair loss in men and women.     

Chronic telogen effluvium is due to a reduction in the variance of anagen duration

Background/Objectives: Chronic telogen effluvium and diffuse cyclical hair loss in women are well‐described clinical entities characterized by chronic and fluctuating increases in hair shedding without loss of hair volume. We sought to investigate the follicular dynamics of chronic telogen effluvium and diffuse cyclical hair loss using a previously validated computer simulation known as the follicular automaton. Methods: Using our model, we were able to simulate reductions in both the mean and variance of anagen duration and thus investigate their consequences with respect to both hair volume and hair shedding. Results: We showed that reducing the mean anagen duration results in a loss of hair volume without prominent fluctuations in hair fall: findings that reproduced the key features in androgenetic alopecia. In contrast, a reduction in the variance of anagen duration generated follicular dynamics that accurately reproduced the known key features of chronic telogen effluvium and diffuse cyclical hair loss: acute exacerbations, periodicity and only minimal reductions in long‐term hair volume. Conclusions: We provide evidence that suggests chronic telogen effluvium may be secondary to a reduction in the variance of anagen and suggest this pathological state represents a new functional type of recurrent hair shedding.     

Telogen skin contains an inhibitor of hair growth

We have investigated whether C57B1-6 mouse skin with all its follicles in the telogen stage of the hair cycle contains a hair-growth inhibitory activity, as opposed to skin with anagen follicles. Crude aqueous extracts of whole telogen mouse skin (TE), anagen skin (AE) or vehicle alone (V) were injected intraperitoneally into mice in which anagen had previously been induced by plucking of telogen hair follicles. Injection of TE, but not AE or V, significantly retarded the development of anagen follicles, as measured by macroscopic and quantitative microscopic hair growth parameters (skin pigmentation and thickness, appearance of trichohyaline granules) and the incorporation of tritiated thymidine into mouse skin from animals previously treated with either TE or V (skin organ culture). This inhibitory activity seemed to be localized to the epidermis and was also present in rat epidermis. We suggest that this apparently non-species-specific inhibitor present in telogen skin may play a role in regulating the hair cycle in rodents.     

Histopathological insights into hair loss in Cronkhite–Canada syndrome: Diffuse anagen‐telogen conversion precedes clinical hair loss progression

Cronkhite–Canada syndrome (CCS) is a rare disorder characterised by gastrointestinal polyposis and ectodermal changes, represented by extensive alopecia. Detailed histopathological investigations of alopecic lesions in two female CCS patients with severe hair loss revealed a marked increase in telogen hair follicles with no sign of loss or of the minaturisation or atrophy of hair follicle structures and the absence of inflammatory change, despite severe inflammation in the gastrointestinal tract. These findings suggested that hair regrowth can be expected without systemic corticosteroids, if they are not necessary for treatment of the gastrointestinal tract, and that anagen‐telogen transition is an early event preceding clinical hair loss in CCS.     

Overexpression of skin protein kinase C-alpha in anagen hair follicles during induced growth of mouse hair

A role for protein kinase C (PKC)-alpha has been implicated in the growth of mouse hair. Topical application of PKC activators, hair plucking, allergic contact dermatitis and skin irritation can all enhance growth of mouse hair, and a significant increase in PKC-alpha level in whole mouse skin in mature anagen has been demonstrated in these processes. Overexpression of PKC-alpha in anagen hair follicles has also been reported in natural growth of mouse hair. It is known that overexpression of PKC-alpha is associated with the acceleration of cell growth. Therefore, we postulated that overexpression of PKC-alpha in mature anagen may relate to enhancement of hair growth. The distribution of PKC-alpha in hair follicles during induced growth of mouse hair has not previously been studied. In this study, hair growth in C57BL/6 mice was induced by plucking the telogen hairs on one side of the back. The undepilated contralateral side served as a control. Expression of PKC-alpha in hair follicles during the hair growth cycle induced was evaluated by immunohistochemistry using cryosections and a specific polyclonal anti-PKC-alpha immunoglobulin G (IgG) antibody. No PKC-alpha was detected in telogen hair follicles or in the hair follicles at 1 day post-depilation, when the induced hair cycle was in early anagen. At 4 days after plucking, when the induced hair cycle was in mid-anagen, intense staining for PKC-alpha was found in hair papillae. At 10 and 17 days after depilation, when the induced hair cycle was in mature anagen and early catagen, respectively, all outer root sheath (ORS) cells and outer connective sheaths of hair follicles were stained positive. Because no PKC-alpha was detected in telogen hair follicles in this study, down-regulation of PKC-alpha in early anagen could not be observed. However, consistent with our previous findings, overexpression of PKC-alpha was found in mid-anagen and mature anagen. As overexpression of PKC-alpha has been shown to be associated with acceleration of cell growth, our results support the notion that PKC-alpha may play an important role in growth of hair follicle cells in induced growth of hair. As PKC levels are known to increase in hyperglycaemia, overexpressed PKC-alpha in mature anagen hair follicles may be related to the putative function of the ORS in mobilizing glycogen stores for anagen growth.     

A systematic review of light-based home-use devices for hair removal and considerations on human safety

Background Hair removal with professional light‐based devices is established as an effective, mainstream treatment. The field of optical home‐based hair removal is evolving and movement from control by physicians into hands of consumers warrants understanding efficacy and human safety. Objectives To systematically review and evaluate the efficacy and human safety of currently available home‐based optical hair removal devices. Methods A comprehensive Pub Med literature search was conducted which systematically identified publications of relevance. Prospective clinical trials were included whether controlled, uncontrolled or randomized and with a sample size of at least 10 individuals. Results We identified a total of seven studies: one controlled (CT) and six uncontrolled trials (UCTs). No randomized controlled trials (RCT) were recognized. The best evidence was found for IPL (intense pulsed light) (three devices, one CT, five UCTs) and limited evidence for laser devices (one diode laser, one UCT). Most studies evaluated short‐term hair reduction up to 3 and 6 months following light exposure at different body sites. Hair reduction percentages ranged from 6% to 72% after repetitive treatments. The most frequently reported side‐effect was erythema, but oedema, blistering, crusting and pigment changes were also reported. Theoretical concerns about ocular damage and paradoxical hair growth have not been reported in any of the studies reviewed. Conclusions Available evidence from prospective, uncontrolled clinical trials indicates short‐term hair removal efficacy of currently available home‐use light‐based hair removal devices. Additional controlled trials will be helpful to substantiate the efficacy and to better predict the incidence of adverse events associated with optical home‐use hair removal.     

Hair cycle resting phase is regulated by cyclic epithelial FGF18 signaling

Hair follicles repeatedly cycle through growth (anagen), regression (catagen), and resting (telogen) phases. Although the signaling molecules involved in the anagen and anagen-catagen transition have been studied extensively, the signaling that controls telogen is only partly understood. Here we show that fibroblast growth factor (Fgf)18 is expressed in a hair stem cell niche throughout telogen, and that it regulates the hair cycle through the non-growth phases. When the Fgf18 gene is conditionally knocked out in keratin 5-positive epithelial cells in mice, telogen becomes very short, giving rise to a strikingly rapid succession of hair cycles. In wild-type mice, hair follicle growth during anagen is strongly suppressed by local delivery of FGF18 protein. Our results demonstrate that epithelial FGF18 signaling and its reduction in the milieu of hair stem cells are crucial for the maintenance of resting and growth phase, respectively.     

Regulation of Hair Shedding by the Type 3 IP(3) Receptor

Here we showed that the type 3 IP(3) receptor (IP(3)R3) is specifically expressed in hair follicles of the skin and plays an important role in the regulation of the hair cycle. We found that IP(3)R3-deficient (Itpr3(-/-)) mice had prominent alopecia, which was characterized by repeated hair loss and regrowth. The alopecic stripe runs along the body axis like a wave, suggesting disturbed hair-cycle regulation. Indeed, the hair follicles of the alopecic region were in the early anagen stage. Although the hair growth and proliferation activity of the hair matrix cells in the anagen phase were normal in Itpr3(-/-) mice, telogen club hairs in the telogen-anagen transition phase were loosely attached to the hair follicles and were easily removed in contrast to the more tightly attached club hairs of Itpr3(+/+) mice. Itpr3(-/-) keratinocytes surrounding the telogen club hairs have sparse cytokeratin filaments extending in random directions, as well as less developed desmosomes. Furthermore, nuclear factor of activated T cells c1 (NFATc1) failed to translocate into the nucleus of keratin 6-positive bulge cells in Itpr3(-/-) telogen follicles. We propose that hair shedding is actively controlled by the IP(3)R3/NFAT-dependent signaling pathway, possibly through the regulation of cytokeratin filaments in keratinocytes.     

Effect of hair growth cycles on experimental cutaneous candidiasis in mice

Experimental cutaneous Candida albicans infections were produced in mice by inoculating the organisms onto areas of shaved flank skin where the hair follicles were in either the anagen (growing) or telogen (resting) phase of the growth cycle. Infection with Candida occurred in a majority of animals inoculated on either anagen or telogen skin, and the rate of clearance of the organisms was equivalent for infections on the 2 types of skin. Some of the animals inoculated on anagen skin developed foci of Candida infection in the well-developed hair follicles, below the skin surface. Deep foci of infection were not found after inoculation of the telogen areas. The infections resulted in increases in epidermal thickness and sensitization of the animals to Candida antigens, but these responses were not different between animals inoculated on the 2 types of skin. The results of these experiments indicate that although Candida albicans can infect skin containing either active or resting hair follicles, foci of infection below the skin surface occur only when well-developed hair follicles are present. These findings may have relevance to the consequences of human cutaneous candidiasis.     

Topical application of cyclosporin A induces rapid-remodeling of damaged anagen hair follicles produced in cyclophosphamide administered mice.

Adult C3H mice which had either anagen IV or anagen VI hair follicles were given the anti-tumor drug cyclophosphamide, and cyclosporin A or minoxidil were topically applied to the mice daily from the 4th day after cyclophosphamide administration. In the mice that had anagen IV-hair follicles, 0.5% cyclosporin A induced very thick and long hairs after 21 days of cyclophosphamide administration, while vehicle and 1% minoxidil induced sparsely visible, short hairs. In the mice which received cyclosporin A, the injured hair follicles seemed to remodel themselves into intact anagen hair follicles and restart the production of hairs, instead of shifting to telogen. In the mice that had anagen VI-hair follicles at the time of cyclophosphamide administration, complete alopecia occurred within the first 7 days in all groups. After 14 days of cyclophosphamide administration, hair regrowth was observed in both the 0.5% cyclosporin A-group and the 1% minoxidil- group with the predominant effect over the vehicle. This study shows that anagen hair follicles respond to cyclophosphamide in different ways depending on their stages (IV and VI), and that the damaged anagen IV hair follicles have the potential of remodeling themselves, which is promoted by topical cyclosporin A administration.     

Hair cycle control by leptin as a new anagen inducer

Our purpose is to clarify the physiological role of leptin in hair cycle as leptin reportedly causes activation of Stat3, which is indispensable for hair cycling. While hair follicles in dorsal skin of 5‐week‐old C57/BL6 mice had progressed to late anagen phase, those in dorsal skin of 5‐week‐old leptin receptor deficient db/db mice remained in the first telogen and later entered the anagen at postnatal day 40, indicating that deficiency in leptin receptor signalling delayed the second hair cycle progression. Next, we shaved dorsal hairs on wild‐type mice at postnatal 7 weeks and injected skin with mouse leptin or a mock. After 20 days, although mock injection showed no effect, hair growth occurred around leptin injection area. Human leptin fragment (aa22–56) had similar effects. Although the hair cycle of ob/ob mice was similar to that of wild‐type mice, injection of mouse leptin on ob/ob mice at postnatal 7 weeks induced anagen transition. Immunohistochemically, leptin is expressed in hair follicles from catagen to early anagen in wild‐type mice, suggesting that leptin is an anagen inducer in vivo. Phosphorylation of Erk, Jak2 and Stat3 in human keratinocytes was stimulated by leptin and leptin fragment. In addition, RT‐PCR and ELISA showed that the production of leptin by human dermal papilla cells increased under hypoxic condition, suggesting that hypoxia in catagen/telogen phase promotes leptin production, preparing for entry into the next anagen. In conclusion, leptin, a well‐known adipokine, acts as an anagen inducer and represents a new player in hair biology.     

Proposal and evaluation of a Monte Carlo model for hair regrowth following plucking

Background/aims: The efficacy of single or multiple hair removal treatments reveals a number of properties of the hair follicle, such as the phase in the growing cycle and the hair growth speed. The aim of the present study was to provide a method to evaluate the results of hair removal treatments, in particular plucking, in order to obtain insight into some properties of the follicle and to propose a strategy for optimal treatment. Our hypothesis is that plucking of anagen hairs may result in either reset of the follicle to telogen, in mild damage to the follicle, resulting in a temporary reduction of the mitotic activity, or in an unaffected follicle, so that the hair continues to grow. Methods: The regrowth of hairs after plucking was measured as a function of time for a number of subjects. Individual leg hairs within the areas observed were followed over time. Besides this, the growth speed of leg hairs was measured, and the extracted anagen hair length was determined to obtain an estimate of the anagen follicle depth on the leg. Monte Carlo simulations of the hair plucking and regrowth process were performed after the experiments. Some parameters derived from the experiments were used as inputs; others were fitted to achieve a good correlation between the result of the simulations and the experiments. Finally, the Monte Carlo routine was used to investigate the influence of the time interval between multiple plucking treatments. Results: The regrowth of hairs after plucking, the growth speed and the extracted anagen hair length were measured. Both experiments and Monte Carlo simulations indicated that the result of plucking of an anagen hair is not limited to reset of the follicle to telogen or continued hair growth, but that a temporary reduction of the mitotic activity is very likely to occur. Finally, a linear relationship between the interval between epilation treatments and the average number of hairs on the skin was found using the Monte Carlo simulation. Conclusions: The combination of experiments and Monte Carlo simulations is a very successful strategy for studying hair removal and hair (re)growth in detail.