Hair Regrowth In Mice Research Articles

Promotion of hair growth by a conditioned medium from human umbilical cord mesenchymal stem cells cultivated in a 3D scaffold of gelatin sponge

BackgroundThis study aims to investigate the effects of a conditioned medium (CM) from human umbilical cord mesenchymal stem cells (HuMSCs) cultivated in gelatin sponge (GS-HuMSCs-CM) on hair growth in a mouse model.MethodsCM was collected from the HuMSCs cultivated in a monolayer or in a gelatin sponge. Vascular endothelial growth factor (VEGF), insulin-like growth factor-1 (IGF-1), keratinocyte growth factor (KGF), and hepatocyte growth factor (HGF) levels in CMs were measured by enzyme-linked immunosorbent assays (ELISAs). A hair loss model by a C57 BL/6J mouse was prepared. The effects of GS-HuMSCs-CM and HuMSCs on hair regrowth in mice were investigated by intradermal injection in the depilated back skin with normal saline (NS) as the control. The time for hair regrowth and full covering in depilated areas was observed, and the hair growth was evaluated histologically and by grossly measuring hair length and diameter.ResultsCompared with monolayer cultured cells, the three-dimensional (3D) culture of HuMSCs in gelatin sponge drastically increased VEGF, IGF-1, KGF, and HGF production. GS-HuMSCs-CM and HuMSCs injection both promoted hair regeneration in mice, while GS-HuMSCs-CM presented more enhanced effects in hair length, hair diameter, and growth rate. GS-HuMSCs-CM significantly promoted angiogenesis in injected skin areas, which might also contribute to faster hair regrowth.ConclusionGS-HuMSCs-CM exerted significant effects on inducing hair growth and promoted skin angiogenesis in C57BL/6J mice.

Ellagic acid inhibits dihydrotestosterone-induced ferroptosis and promotes hair regeneration by activating the wnt/β-catenin signaling pathway

Ethnopharmacological relevanceAndrogenic alopecia (AGA) is the most prevalent form of hair loss in clinical practice and affects the physical and psychological well-being of adolescents. Paeonia lactiflora Pallas (PL), which is widely used in traditional Chinese medicine, enhances blood function and promotes hair growth, and ellagic acid (EA), a polyphenol in PL extract, shows strong antioxidant, anti-aging, and anti-inflammatory properties and also plays a role in the treatment of various skin conditions. However, its role and mechanism of action in AGA remain unclear. Aim of the studyTo determine whether EA can rescue slow hair regeneration by regulating dihydrotestosterone (DHT)-induced ferroptosis in AGA mice and clarify the effect of EA on DHT-induced ferroptosis in dermal papilla cells (DPCs). Materials and methodsMale C57BL/6 mice were used to establish a DHT-induced AGA mouse model, whereas DPCs were used to establish a DHT-induced cellular model. Thereafter, we investigated the therapeutic mechanism of action of EA via immunofluorescence, western blot analysis, immunohistochemistry, electron microscopy, and molecular docking. ResultsEA stimulated hair regeneration in mice and reversed DHT-induced increases in iron content, lipid peroxidation, and DHT-induced mitochondrial dysfunction by activating the Wnt/β-catenin signaling pathway. Further, β-catenin knockdown suppressed the inhibitory effect of EA on DHT-induced ferroptosis in DPCs. ConclusionEA inhibits DHT-induced ferroptosis and promotes hair regrowth in mice by activating the Wnt/β-catenin signaling pathway. Thus, it has potential for use as a treatment option for AGA.

Promotion of Hair Regrowth in Androgenetic Alopecia with Supplemented Erzhi Wan: Exploring Its Mechanism Using Network Pharmacology and Molecular Docking.

Supplemented Erzhi Wan (SEZW) is a Traditional Chinese Medicine commonly used in the treatment of androgenetic alopecia (AGA). This study aims to verify the effectiveness of SEZW for the treatment of AGA in mice and explore the potential molecular mechanisms underlying its function using network pharmacology and molecular docking. Forty mice were divided into five groups: Control, AGA-model, AGA-Positive, SEZW Low Dose, and SEZW High Dose. Hair regrowth in mice was evaluated by scoring hair on days 0, 14, and 28 post-treatment and weighing mouse hair on day 28 post-treatment. The targets of the active compounds of SEZW were obtained using the Traditional Chinese Medicine Database. AGA-related targets were downloaded from five databases. Then, the overlapping genes were identified. A protein-protein interaction network was constructed using the STRING database. Hub targets were determined through analysis. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed. Finally, molecular docking of active compounds and hub targets was performed. Hair regrowth in mice in the SEZW treatment groups was significantly enhanced relative to that in the AGA-model mice. A total of 59 potential drug-disease targets were identified. Based on the GO/KEGG analysis results, oxidative stress and gland development were identified as potential mechanisms of action of SEZW in AGA treatment. The PI3K-Akt and AGE-RAGE signaling pathways and seven hub targets were identified as the potential underlying mechanism of SEZW function. Molecular docking results showed that the most active SEZW compounds bind stably to several of the candidate disease targets. SEZW is effective in the treatment of AGA in a mouse model. Combined with network pharmacological analysis, the potential mechanisms, signaling pathways, and hub targets of SEZW in the treatment of AGA were identified, providing new ideas for further studies.

Heat-Killed Enterococcus faecalis EF-2001 Induces Human Dermal Papilla Cell Proliferation and Hair Regrowth in C57BL/6 Mice.

Minoxidil is the most widely used treatment for hair growth, but has been associated with several side effects. In this study, we investigated the effects of heat-killed Enterococcus faecalis EF-2001 on hair loss prevention and regrowth using human dermal papilla cells and male C57BL/6 mice. To examine the effects of EF-2001, we used minoxidil as the positive control. In the in vitro experiments, EF-2001 treatment (75–500 μg/mL) led to the proliferation of human dermal papilla cells in a concentration-dependent manner. In the in vivo experiment, the topical application of 200 µL EF-2001 on the dorsal surface of C57BL/6 male mice led to hair growth. Changes in hair regrowth were examined by visual comparison and hematoxylin and eosin staining of skin sections. We also determined the expression levels of marker genes (Wnt) and growth factors (fibroblast growth factor, insulin growth factor 1, and vascular endothelial growth factor) in the skin tissues of the back of each mouse using a quantitative polymerase chain reaction. EF-2001 accelerated the progression of hair regrowth in mice and promoted hair-follicle conversion from telogen to anagen, likely by increasing the expression levels of growth factors and marker genes.

Potential of Colostrum-Derived Exosomes for Promoting Hair Regeneration Through the Transition From Telogen to Anagen Phase.

Human hair dermal papillary (DP) cells comprising mesenchymal stem cells in hair follicles contribute critically to hair growth and cycle regulation. The transition of hair follicles from telogen to anagen phase is the key to regulating hair growth, which relies heavily on the activation of DP cells. In this paper, we suggested exosomes derived from bovine colostrum (milk exosomes, Milk-exo) as a new effective non-surgical therapy for hair loss. Results showed that Milk-exo promoted the proliferation of hair DP cells and rescued dihydrotestosterone (DHT, androgen hormones)-induced arrest of follicle development. Milk-exo also induced dorsal hair re-growth in mice at the level comparable to minoxidil treatment, without associated adverse effects such as skin rashes. Our data demonstrated that Milk-exo accelerated the hair cycle transition from telogen to anagen phase by activating the Wnt/β-catenin pathway. Interestingly, Milk-exo has been found to stably retain its original properties and efficacy for hair regeneration after freeze-drying and resuspension, which is considered critical to use it as a raw material applied in different types of alopecia medicines and treatments. Overall, this study highlights a great potential of an exosome from colostrum as a therapeutic modality for hair loss.

Engineered extracellular vesicle mimetics from macrophage promotes hair growth in mice and promotes human hair follicle growth

Recent studies clearly show that cell-derived extracellular vesicles (EVs, including exosomes) can promote hair growth. However, large-scale production of EVs remains a big hurdle. Recently, extracellular vesicle mimetics (EMs) engineered by extrusion through various membranes are emerging as a complementary approach for large-scale production. In this study, to investigate their ability to induce hair growth, we generated macrophage-engineered EMs (MAC-EMs) that activated the human dermal papilla (DP) cells in vitro. MAC-EMs intradermally injected into the skin of C57BL/6 mice were retained for up to 72 h. Microscopy imaging revealed that MAC-EMs were predominately internalized into hair follicles. The MAC-EMs treatment induced hair regrowth in mice and hair shaft elongation in a human hair follicle, suggesting the potential of MAC-EMs as an alternative to EVs to overcome clinical limitation.

KY19382, a novel activator of Wnt/β-catenin signalling, promotes hair regrowth and hair follicle neogenesis.

Background and PurposeThe promotion of hair regeneration and growth heavily depends on the activation of Wnt/β‐catenin signalling in the hair follicle, including dermal papilla (DP). KY19382, one of the newly synthesized analogues of indirubin‐3′‐monoxime (I3O), was identified as a Wnt/β‐catenin signalling activator via inhibition of the interaction between CXXC‐type zinc finger protein 5 (CXXC5) and dishevelled (Dvl). Given the close relationship between the Wnt/β‐catenin signalling and hair regeneration, we investigated the effect of KY19382 on hair regrowth and hair follicle neogenesis.Experimental ApproachIn vitro hair induction effects of KY19382 were performed in human DP cells. The hair elongation effects of KY19382 were confirmed through the human hair follicle and vibrissa culture system. In vivo hair regeneration abilities of KY19382 were identified in three models: hair regrowth, wound‐induced hair follicle neogenesis (WIHN) and hair patch assays using C57BL/6 mice. The hair regeneration abilities were analysed by immunoblotting, alkaline phosphatase (ALP) and immunohistochemical staining.Key ResultsKY19382 activated Wnt/β‐catenin signalling and elevated expression of ALP and the proliferation marker PCNA in DP cells. KY19382 also increased hair length in ex vivo‐cultured mouse vibrissa and human hair follicles and induced hair regrowth in mice. Moreover, KY19382 significantly promoted the generation of de novo hair follicles as shown by WIHN and hair patch assays.Conclusion and ImplicationsThese results indicate that KY19382 is a potential therapeutic drug that exhibits effective hair regeneration ability via activation of the Wnt/β‐catenin signalling for alopecia treatments.

Oral ruxolitinib induces hair regrowth in patients with moderate-to-severe alopecia areata.

BACKGROUND. Alopecia areata (AA) is a common autoimmune disease with a lifetime risk of 1.7%; there are no FDA-approved treatments for AA. We previously identified a dominant IFN-γ transcriptional signature in cytotoxic T lymphocytes (CTLs) in human and mouse AA skin and showed that treatment with JAK inhibitors induced durable hair regrowth in mice by targeting this pathway. Here, we investigated the use of the oral JAK1/2 inhibitor ruxolitinib in the treatment of patients with moderate-to-severe AA. METHODS. We initiated an open-label clinical trial of 12 patients with moderate-to-severe AA, using oral ruxolitinib, 20 mg twice per day, for 3-6 months of treatment followed by 3 months follow-up off drug. The primary endpoint was the proportion of subjects with 50% or greater hair regrowth from baseline to end of treatment. RESULTS. Nine of twelve patients (75%) demonstrated a remarkable response to treatment, with average hair regrowth of 92% at the end of treatment. Safety parameters remained largely within normal limits, and no serious adverse effects were reported. Gene expression profiling revealed treatment-related downregulation of inflammatory markers, including signatures for CTLs and IFN response genes and upregulation of hair-specific markers. CONCLUSION. In this pilot study, 9 of 12 patients (75%) treated with ruxolitinib showed significant scalp hair regrowth and improvement of AA. Larger randomized controlled trials are needed to further assess the safety and efficacy of ruxolitinib in the treatment of AA. TRIAL REGISTRATION. Clinicaltrials.gov NCT01950780. FUNDING. Locks of Love Foundation, the Alopecia Areata Initiative, NIH/National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), and the Irving Institute for Clinical and Translational Research/Columbia University Medical Center Clinical and Translational Science Award (CUMC CTSA).

The Success of Thread-embedding Therapy in Generating Hair Re-growth in Mice Points to Its Possibly Having a Similar Effect in Humans.

Objectives:Recently, thread-embedding therapy (TET) has been widely applied in Korean medicine for cosmetic purposes such as reducing skin wrinkles. An inserted thread was reported to have induced continuous stimulation, followed by support for connective tissue regeneration. However, the potential role of TET in hairgrowth has not yet been reported.Methods:We designed this study to evaluate whether TET has a hair-growth-promoting effect. C57 black 6 (C57BL/6) mice were divided into three groups: normal saline-treated, minoxidil-treated, and thread-embedded groups. Normal saline or 5% minoxidil was topically sprayed on the dorsal skin of the mice once a day for 16 days. Medical threads were embedded into the dorsal skin of the mice in a single application. Hair growth activity was evaluated by using dermoscopic and microscopic observations. Sections of the dorsal skin were stained with hematoxylin and eosin. Expressions of bromodeoxyuridine (BrdU), proliferating cell nuclear antigen (PCNA), fibroblast growth factor-7 (FGF-7), and fibroblast growth factor-5 (FGF-5) were detected by using immunohistochemical staining. A reverse transcription-polymerase chain reaction (RT-PCR) analysis was adopted to measure the messenger RNA (mRNA) expressions of FGF-7 and FGF-5.Results:TET enhanced anagen development in the hair follicles of C57BL/6 mice. The expressions of BrdU and PCNA, both of which imply active cellular proliferation, were increased by using TET. Moreover, TET increased the expression of FGF-7, an anagen-inducing growth factor, while decreasing the expression of FGF-5, an anagen-cessation growth factor, both at the protein and the mRNA levels.Conclusion:TET enhanced hair re-growth in C57BL/6 mice. TET regulated the expressions of anagen-associated growth factors and activated the proliferation of hair follicular cells in depilated skin lesions. Considering its long-lasting effect, TET may be a good alternative therapeutic for the treatment of alopecia.

Colorimetry provides a rapid objective measurement of de novo hair growth rate in mice

Depilated mice have been used as a test platform for hair growth-regulating agents. However, currently available assessment tools for hair growth in mice are less than ideal. Tristimulus colorimetry of the fur color of depilated agouti, albino, and black mice with L*, a*, and b* values were performed daily until the full growth of pelage. Using light-emitting diode (LED) irradiation (650 and 890 nm) with a daily dose of 3.5 J/cm(2) as hair growth regulators, the hair growth rates observed by the global assessment were compared with those derived from colorimetry. In contrast to a* and b* values, L* values changed more drastically over time in the anagen phase regardless of fur color. Unlike the inhibitory effect of 650 nm irradiation, LED of 890 nm promoted de novo hair regrowth in mice. The difference in hair growth rates detected by colorimetry paralleled the observation made by the global assessment. The L* value of fur color obtained by tristimulus colorimetry was a sensitive yet quantitative indicator of de novo hair growth, and could be used to project the hair growth rate in mice.

Increased Rate of Hair Regrowth in Mice with Constitutive Overexpression of Del1

Developmental endothelial locus (Del)1 is a secreted extracellular matrix-associated protein that stimulates angiogenesis through integrin binding and is implicated in vasculogenesis. We hypothesized that increased expression of an angiogenic factor would lead to enhanced wound healing. Transgenic mice had Del1 cloned behind a keratin 14 promoter (K14-Del1) to drive constitutive expression in basal keratinocytes. Transgenic animals and wild-type litter mates underwent excisional wounding or depilation, and tissues were harvested at various time points. Wound healing and hair regrowth were assessed by photography, histology, and immunohistochemistry. For injection experiments, purified Del1 protein was injected in the flanks of wild-type mice with carrier on the contralateral flank as a control. Del1 expression during hair development was performed using transgenic mice with a LacZ cassette introduced downstream from the native promoter. K14-Del1 animals appeared normal and healed excisional wounds normally but demonstrated an increased rate of hair regrowth after wound healing. Using depilation experiments to specifically address hair follicle growth, we found increased hair regrowth was independent of wounding. This was confirmed by injection of purified Del1 protein. During normal hair anagenesis, Del1 is expressed in the root of the hair follicle. Constitutive expression of Del1 in skin does not affect skin vascularity or improve wound healing. Surprisingly, we found the primary effect of constitutive Del1 expression in the basal keratinocytes was increased hair growth following induction of anagenesis. During normal hair anagenesis, we see expression of Del1 in the root of the hair follicle suggesting it may function there to stimulate hair growth.

Prolactin delays hair regrowth in mice

Mammalian hair growth is cyclic, with hair-producing follicles alternating between active (anagen) and quiescent (telogen) phases. The timing of hair cycles is advanced in prolactin receptor (PRLR) knockout mice, suggesting that prolactin has a role in regulating follicle cycling. In this study, the relationship between profiles of circulating prolactin and the first post-natal hair growth cycle was examined in female Balb/c mice. Prolactin was found to increase at 3 weeks of age, prior to the onset of anagen 1 week later. Expression of PRLR mRNA in skin increased fourfold during early anagen. This was followed by upregulation of prolactin mRNA, also expressed in the skin. Pharmacological suppression of pituitary prolactin advanced dorsal hair growth by 3.5 days. Normal hair cycling was restored by replacement with exogenous prolactin for 3 days. Increasing the duration of prolactin treatment further retarded entry into anagen. However, prolactin treatments, which began after follicles had entered anagen at 26 days of age, did not alter the subsequent progression of the hair cycle. Skin from PRLR-deficient mice grafted onto endocrine-normal hosts underwent more rapid hair cycling than comparable wild-type grafts, with reduced duration of the telogen phase. These experiments demonstrate that prolactin regulates the timing of hair growth cycles in mice via a direct effect on the skin, rather than solely via the modulation of other endocrine factors.

A Short Peptide GPIGS Promotes Proliferation of Hair Bulb Keratinocytes and Accelerates Hair Regrowth in Mice

The aim of this study was to discover a novel agent that promotes hair growth. We carried out a screening test in 298 types of conditioned medium (CM) from cultures of bacteria by using a hair bulb keratinocyte (HBK) growth assay. As a result, we found a HBK growth factor in the CM of Bacillus sp. M18. This HBK growth factor was purified by collecting biologically active fractions in three steps, including HP-20 batch processing, LH-20 chromatography and C18 reverse-phase high-pressure liquid chromatography, and identified as a short peptide GPIGS. GPIGS increased Akt phosphorylation in HBKs. Moreover, the GPIGS-stimulated HBK growth was inhibited by the treatment with LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI-3K). These results suggest that GPIGS promotes HBK growth via the PI-3K/Akt pathway. In addition to in vitro tests, GPIGS was found to accelerate hair regrowth in telogen mice. Our results indicate that GPIGS is a potential agent to promote hair growth.

Increased rate of hair regrowth in mice with constitutive over expression of the angiogenic factor Del1 in basal keratinocytes

Abstract Introduction: Del1 is a secreted extracellular matrix-associated protein that stimulates angiogenesis through integrin binding and is implicated in vasculogenesis. We used transgenic mice engineered to over-express Del1 in the skin to examine the effect of increased Del1 in wound healing. No effect was found on wound healing, but we found an increased rate of hair regrowth. Methods: Del1 was cloned behind a keratin 14 promoter (K14-Del1) that drives constitutive expression in the basal keratinocytes and this construct was used to generate two separate transgenic mouse lines. 6–8 week old transgenic animals were shaved and depilated with Nair along the posterior midline. Wild-type littermates were used as controls, and tissues were harvested at 10, 12, 14, 15, and 18 days post-depilation. Progress of hair regrowth was followed by photography, histology, and immunohistochemistry. Results: K14-Del1 animals appear normal and heal excisional wounds normally. Immunohistochemistry confirmed increased Del1 expression, but indicated no increase in vascularity. Following depilation, hair regrowth was grossly visible by day 15 in littermates compared to day 18 for normals. Full-length hair follicles were visible by histology at post-depilation day 15 in K14-Del1 animals, while wild type animals showed very rudimentary hair-follicle regeneration. Conclusions: Constitutive expression of Del1 in skin does not appear to increase vascularity or improve wound healing. Surprisingly, we found this led to increased hair regrowth following depilation. Depilation is a known inducer of hair anagenesis and Del1 appears to speed this process. Future studies will elucidate a mechanism for this phenotype.

Topical Estrogen Accelerates Hair Regrowth in Mice After Chemotherapy-Induced Alopecia by Favoring the Dystrophic Catagen Response Pathway to Damage

Estrogen receptor ligands are important modulators of skin physiology and are involved in the control of normal hair follicle cycling. Here, we have studied the effects of topically applied 17-beta-estradiol on pathologic hair follicle cycling as seen during chemotherapy-induced alopecia, one of the major unresolved problems of clinical oncology. For this study we employed a well-established murine model that mimics chemotherapy-induced alopecia in humans. For precisely quantifying the area of hair loss and hair regrowth in this model in vivo, we developed a simple planimetric assay (dotmatrix planimetry). We show that topical 17-beta-estradiol significantly alters the cycling response of murine follicles to cyclophosphamide, whereas the estrogen antagonist ICI 182.780 exerted no such effects. Initially, topical 17-beta-estradiol enhanced chemotherapy-induced alopecia significantly by forcing the follicles into the dystrophic catagen response pathway to hair follicle damage, whereas follicles treated by ICI 182.780 or vehicle shifted into the dystrophic anagen response pathway. Consequently, the regrowth of normally pigmented hair shafts after chemotherapy-induced alopecia was significantly accelerated in the 17-beta-estradiol treated group. Our data encourage one to explore topical estrogens as a potential stimulant for hair re-growth after chemotherapy-induced alopecia.

Effect of adenovirus-mediated expression of Sonic hedgehog gene on hair regrowth in mice with chemotherapy-induced alopecia.

The Sonic hedgehog (Shh) gene is involved in the initiation of hair growth. We have shown that localized, transient, enhanced expression of the Shh gene in mouse skin mediated by an adenovirus (AdShh) vector accelerates initiation of the anagen (i.e., growth) phase of hair follicle development. Because hair regrowth in chemotherapy-induced alopecia is associated with follicle cell proliferation and active melanogenesis similar to that observed in the anagen phase of normal hair growth, we examined whether AdShh-mediated Shh expression would accelerate hair regrowth in the skin of mice with chemotherapy-induced alopecia. After establishment of cyclophosphamide-induced alopecia, in either 3- or 7-week-old mice, AdShh or a control vector (AdNull) was delivered to dorsal skin by intradermal injection. Hair regrowth and melanogenesis were assessed by histology and gross morphology. Fisher's exact test was used to compare differences in outcomes between AdShh-treated and control (AdNull-treated or not injected with any vector [naive]) mice. All statistical tests were two-sided. Northern blot analysis confirmed enhanced Shh expression after AdShh administration in 7-week-old mice. Two weeks after AdShh administration, the injection site (all of five mice) showed large, anagen-phase hair follicles with a normal distribution of melanin. In contrast, both skin treated with AdNull (all of five mice) and skin from naive mice (all of five mice) showed dystrophic hair follicles with irregular distribution of melanin (P<.001 in both comparisons). Gross morphologic observations confirmed that AdShh-treated mice, but not naive mice or AdNull-treated mice, showed skin darkening at the injection site indicative of entry into anagen phase (P<.001 in both comparisons). AdShh treatment of 3-week-old mice with cyclophosphamide-induced alopecia was followed by accelerated hair follicle recovery (19 of 22 mice); such recovery was not observed at this rate in AdNull-treated or naive skin (P<.001 for both comparisons). Localized, transient, enhanced expression of Shh gene in skin, mediated by an adenovirus vector, might be a future strategy to accelerate hair follicle regrowth after chemotherapy-induced alopecia.

Delay of Hair Regrowth in Mice as a Possible Biological Dosimeter on the Skin in Case of Over Exposure.

The delay of hair regrowth of mice after irradiation was examined to investigate its possibility as a biological dosimeter in the cases of localized over exposure. Hairs on the dorsal skin of mice were shaved and irradiated with a 90Sr/90Y β-ray source in early anagen or midanagen stage of hair cycle. Skin doses were 0.5-10Gy and 1-4Gy, respectively. Hair regrowth was observed with a scaling loupe. Hair regrowth delay was dose dependent, fitting the linear-quadratic function and the linear function according to the stages of hair. Histological observations indicated that the hair matrix cells death was the main cause of hair regrowth delay in the midanagen stage. Dose estimation functions, derived from the dose-effect relationship curves, could be applied for the dosimetey of the skin over exposure. It could detect a dose over 1Gy, and as early as a few days after the exposure.

Biochemical analysis of hair growth from the aspects of aging and enzyme activities.

ABSTRACTThe dorsal resting hair of C3H mice was shaved, activating the hair into the anagen stage. Hair regrowth in mice of different ages (10–20 mice in each group), whose hair cycles were in the telogen stage, were compared after shaving. In both groups of mice, new hair growth was not uniform, but irregular on the shaved areas. Delay in hair regrowth increased as the mice became older (20 &lt; 66 &lt; 188 &lt; 312 day old mice). Furthermore, eighteen 59 day‐old mice were used for biochemical analysis. Nine days after shaving, 30–50% of the shaved skin area was covered with new hair. After sacrifice, the dorsal skins were separated into hair re‐growing, non‐growing, and non‐shaved control areas. Several enzyme activities in the extracts from the above‐named areas were compared in terms of “per g of wet weight tissue”, “per mg DNA” and “per mg of soluble protein”. The activities of ornithine decarboxylase (ODC), transglutaminase (TGase) and alkaline phosphatase (Al‐P) were remarkably high in the extract from the hair re‐growing area as compared with that from the non‐growing area. Comparison of the activities of the follicle‐rich fractions from the hair re‐growing area to those of the non‐shaved area showed that ODC, TGase and Al‐P activities were increased.