ArticleLiterature Review

The Biology, Structure, and Function of Eyebrow Hair

Authors:
To read the full-text of this research, you can request a copy directly from the author.

Abstract

Eyebrow hair serves many important biologic and aesthetic functions. This article reviews the structure and function of the hair follicle, as well as hair follicle morphogenesis and cycling. Eyebrow hair follicles share the same basic structure as hair follicles elsewhere on the body, but are distinguished by their shorter anagen (growing) phase. Knowledge of the hair follicle structure and cycle is important for understanding the pathophysiology of alopecia, as diseases affecting the stem cell portion of the hair follicle in the bulge region may cause permanent hair loss. Furthermore, therapeutic agents that target distinct phases and hormones involved in the hair cycle may be useful for promoting hair growth. J Drugs Dermatol. 2014;13(suppl 1):s12-s16.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the author.

... The eyebrow stays in the anagen phase for only 2 to 4 weeks, resulting in short hair. 12,13 Catagen is the regression phase of the hair follicles; it lasts 2 to 3 weeks. Apoptosis of follicular keratinocytes occurs during this phase and leads to the degeneration of the lower portion of hair follicles. ...
... At the end of the catagen phase, the dermal papilla moves upward and rests at the area close to the hair bulge. 13 Telogen is the resting phase of hair follicles; it lasts 2 to 3 months. Approximately 90% of eyebrow hairs are in the telogen phase. ...
... To start the new hair cycle, the dermal papilla stimulates follicular stem cells, known as the bulge activating theory, during late telogen, which leads to the re-entering of the anagen phase. 13 Distinguished hair shedding has been proposed as a separate phase called exogen. During this phase, the old hair is shed, and the new hair shaft grows. ...
Article
Full-text available
Nongsak Chanasumon, Tueboon Sriphojanart, Poonkiat Suchonwanit Division of Dermatology, Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand Abstract: Eyebrows serve as a key feature of the face and have many roles, including cosmetic appearance and social communication. Eyebrow hypotrichosis, which refers to reduction or absence of the eyebrow hair, could be a major problem that leads to negative functional, psychological, and social consequences. Bimatoprost is an ophthalmic prostamide analog that is approved by the United States Food and Drug Administration for the treatment of eyelash hypotrichosis. Its proposed mechanism is stimulation of the prostaglandin receptor in dermal papilla and melanocyte, thus leading to a prolonged anagen phase and increased melanogenesis. The hair follicle then increases in thickness, length, and darkness. The efficacy of bimatoprost for the treatment of eyebrow hypotrichosis has been supported by well-controlled studies. Bimatoprost, which is noninvasive, effective, and well tolerated, is worth considering as a treatment option for eyebrow hypotrichosis. Keywords: bimatoprost, eyebrow, hair, hypotrichosis, prostaglandin, prostamide
... The importance of eyebrows, in general, is well established, and studies show that eyebrows are fundamentally important in emotional expression, communication, facial attractiveness, and facial recognition (Neely et al., 2014;Nguyen, 2014;Sadr et al., 2003). However, there are no studies that specifically investigate the importance of eyebrows to patients with AA. ...
Article
Alopecia areata affects not only scalp hair but also other sites of body hair, including eyebrows. Our objective was to investigate the importance of eyebrows in the treatment goals of patients with alopecia areata. Through an online questionnaire, subjects were asked to assess satisfaction with the visually depicted level of response to treatment, using edited photographs depicting a range of eyebrows and scalp hair growth. The questionnaire was completed by 1,741 adults. Absent or partial growth of eyebrows and scalp hair elicited <25% satisfaction. Images depicting either complete eyebrows or complete scalp hair achieved satisfaction in >50% of participants. More participants were satisfied with complete eyebrows and no scalp hair (69%) than complete eyebrows and partial scalp hair (51%). Only when both eyebrows and scalp hair were completely regrown did extreme satisfaction levels reach 90.4%. Limitations include the online nature of the survey, lack of control group, and self-reported severity of alopecia areata in participants. These results suggest that eyebrows may be as important as scalp hair for patients assessing theoretical responses to treatment for alopecia areata. Future clinical studies should consider growth of eyebrows as an outcome measure on par with scalp hair growth.
... 1,2) Hair basically have biological protective function from its external environments as well as influence social interaction. 3,4) Therefore, hair loss or baldness, correctively known as alopecia, directly distresses self-confidence affecting our daily life. 5) The growing and shape of hair fiber is strictly controlled and generated by the specialized mini-organ, hair follicle (HF) anchoring each hair into the skin. ...
Article
Dermal papilla (DP) is a pivotal part of hair follicle, and the smaller size of the DP is related with the hair loss. In this study, we investigated the effect of titrated extract of Centella asiatica (TECA) on hair growth inductive property on 3D spheroid cultured human DP cells (HDP cells). Significantly increased effect of TECA on cell viability was only shown in 3D sphered HPD cells, not in 2D cultured HDP cells. Also, TECA treatment increased the sphere size of HDP cells. The luciferase activity of STAT reporter genes and the expression of STAT-targeted genes, SOCS1 and SOCS3, were significantly decreased. Also, TECA treatment increased the expression of the hair growth-related signature genes in 3D sphered HDP cells. Furthermore, TECA led to downregulation of the level of phosphorylated STAT proteins in 3D sphered HDP cells. Overall, TECA activates the potential of hair inductive capacity in HDP cells.
... Furthermore, the cycle's length varies within different parts of the body. For eyebrows, the cycle is completed in about four months (6), while it takes the scalp up to 6 years to finish. ...
Article
Objective: A preliminary study was conducted in 17 female volunteers (mean age 29.8 years) to gain deeper insights into the characteristics of terminal Caucasian female body hair of different body parts. The focus on Caucasian women was driven by the high number of different scalp hair phenotypes in this ethnicity and intended to identify relevant differences between body areas to improve body hair removal approaches. Methods: Multiple growth parameters and structural parameters were assessed for hair on the upper arm, forearm, upper leg, lower leg, axilla, and intimate area and compared to scalp data. Results: Especially macroscopic and much less microscopic or hair surface properties differ strikingly in the investigated body areas. Hair density on the body is much lower than on scalp with the highest hair density in the axilla and intimate area. Multi-hair follicular units are described for scalp but were also found to a smaller proportion in the axilla and the intimate area. Substantial percentates of hair triplets are only found on the scalp and intimate area. Hair diameter is highest in the intimate area, followed by axillary and lower leg hair and correlates with a faster hair growth rate. The angle of emerging hair is smallest in the intimate area, axilla and on the lower leg. Hair shafts on the lower leg and in the axilla have most overlapping cuticle layers, but independent of body region no significant differences in the mean thickness of cuticle layers was detectable. In addition, no differences were found in the mean distance between cuticle layer edges along the hair shaft and the hair surface roughness. Hair on the scalp, forearm, upper arm, and upper leg had an almost round shape, whereas hair of the lower leg, intimate area, and axilla had more elliptical shape. Hairs on the arm showed the highest luminance values and no visible medulla. The darkest hairs were in the axilla and intimate area containing the highest level of visible medulla in hair shafts. Conclusion: To our knowledge this is the first systematic study comparing terminal hair properties in all cosmetically relevant body regions in Caucasian women. This article is protected by copyright. All rights reserved.
Article
Dermoscopy is becoming an indispensable tool in everyday practice, with an expanding range of applications. Trichoscopy is effective not only in establishing the diagnosis of scalp disorders but also in the follow‐up of treatment. The MEDLINE database was searched using the terms “dermoscopy” and “trichoscopy” in combination with each of the following: “axilla,” “pubic area,” “beard,” “eyebrows,” “eyelashes,” and “body hairs.” We included case reports, case series, and review articles mentioning the previous terms. By providing an updated review from the literature, we aimed to emphasize the potential uses of trichoscopy in detecting diseases in hairy locations other than the scalp. Various inflammatory conditions, infections, and infestations are discussed.
Chapter
Article
It has long been known that there is a special affinity of psoriasis for the scalp: Here, it occurs most frequently, lesions terminate sharply in frontal skin beyond the hair line and are difficult to treat. Yet, surprisingly, scalp psoriasis only rarely causes alopecia, even though the pilosebaceous unit clearly is affected. Here, we systematically explore the peculiar, insufficiently investigated connection between psoriasis and growing (anagen) terminal scalp hair follicles (HFs), with emphasis on shared regulatory mechanism and therapeutic targets. Interestingly, several drugs and stressors that can trigger/aggravate psoriasis can inhibit hair growth (e.g. beta-blockers, chloroquine, carbamazepine, interferon-alpha, perceived stress). Instead, several anti-psoriatic agents can stimulate hair growth (e.g., cyclosporine, glucocorticoids, dithranol, UV irradiation), while skin/HF trauma (Köbner phenomenon/depilation) favors the development of psoriatic lesions and induces anagen in “quiescent” (telogen) HFs. On this basis, we propose two interconnected working models: a) the existence of a bidirectional “hair follicle-psoriasis axis”, along which keratinocytes of anagen scalp HFs secrete signals that favor the development and maintenance of psoriatic scalp lesions and respond to signals from these lesions, and b) that anagen induction and psoriatic lesions share molecular “switch-on” mechanisms, which invite pharmacological targeting, once identified. Therefore, we advocate a novel, cross-fertilizing and integrative approach to psoriasis and hair research that systematically characterizes the “HF-psoriasis axis”, focused on identification and therapeutic targeting of selected, shared signaling pathways in the future management of both, psoriasis and hair growth disorders.
Article
Background: Differences in growth patterns among the various parts of the eyebrow have been observed. Aims: We aimed to investigate changes in the hair density and diameter and analyze the eyebrow growth pattern of each eyebrow part (head, body, and tail) in patients with eyebrow hypotrichosis over a 24-week course of topical treatment. Patients/methods: A retrospective study of 48 patients who received treatment with bimatoprost 0.01% was conducted. Patient demographic data were collected; measurements of hair density and diameter in the different parts of the eyebrow were collected and statistically evaluated. Results: The tail of the eyebrow revealed the lowest baseline eyebrow density and diameter. Significant changes in eyebrow density (P = .01) and diameter (P = .01) were first detected in the tail at 4 and 16 weeks of treatment, respectively. The head and body showed a comparable growth pattern. Conclusions: This study confirms the previous observations that hair density, diameter, pattern of growth, and hair growth cycle vary according to their anatomical location within the eyebrow. A better understanding of eyebrow growth pattern could provide the precise pathomechanism of eyebrow hypotrichosis leading to a standardized treatment protocol.
Article
Background: Previous studies have proven the efficacy and safety of 0.01% and 0.03% bimatoprost for the treatment of eyebrow hypotrichosis; however, there is no comparison study between both concentrations. Aims: To compare the efficacy and safety between 0.01% and 0.03% bimatoprost for the treatment of eyebrow hypotrichosis. Patients/methods: This prospective, randomized, double-blind, split-face clinical study was conducted in 30 patients with eyebrow hypotrichosis. Each side of eyebrow of individual patients was randomly assigned for 0.01% and 0.03% bimatoprost, applied on each eyebrow once daily. Eyebrow density, diameter, the Global Eyebrow Assessment scale, 7-point rating scale, and patient satisfaction were evaluated. Side effects were also recorded. Results: Both 0.01% and 0.03% bimatoprost significantly improved eyebrow density and diameter (P < .05), although there were no statistically significant differences in changes in eyebrow density and diameter from baseline between both concentrations (P = .96 and .84, respectively). Additionally, patients significantly preferred 0.03% bimatoprost in terms of clinical improvement and satisfaction (P = .04 and .003, respectively). Conclusions: Both 0.01% and 0.03% bimatoprost are effective and safe for the treatment of eyebrow hypotrichosis. Bimatoprost 0.03% is superior to its 0.01% counterpart, albeit without statistical significance.
Article
Eyebrows serve a key role in eye protection, communication, and self-expression. Trends in eyebrow grooming are constantly evolving, often requiring plucking, waxing, or laser hair removal to style. When combined with the natural thinning of the brow with aging, the result can be a sparse or even absent eyebrow hair over time. Follicular unit transplantation provides a means of restoring eyebrow fullness and architecture. With careful attention and augmentation of follicle transfer techniques, a natural end result is possible. © 2015 Wiley Periodicals, Inc.
Article
Parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) influence hair follicles through paracrine and intracrine routes. There is significant evidence that PTH and PTHrP influence the proliferation and differentiation of hair follicle cells. The PTH/PTHrP receptor signalling plays an important role in the hair follicle cycle and may induce premature catagen-telogen transition. Transgenic mice with an overexpression or blockade (PTH/PTHrP receptor knockout mice) of PTHrP activity revealed impaired or increased hair growth, respectively. Some findings also suggest that PTHrP may additionally influence the hair cycle by inhibiting angiogenesis. Antagonists of the PTH/PTHrP receptor have been shown to stimulate proliferation of hair follicle cells and hair growth. A hair-stimulating effect of a PTH/PTHrP receptor antagonist applied topically to the skin has been observed in hairless mice, as well as in mice treated with cyclophosphamide. These data indicate that the PTH/PTHrP receptor may serve as a potential target for new (topical) hair growth-stimulating drugs, especially for chemotherapy-induced alopecia. © 2015 S. Karger AG, Basel.
Article
Full-text available
β-Catenin, a key transducer molecule of Wnt signaling, is required for adult hair follicle growth and regeneration. However, the cellular source of Wnt ligands required for Wnt/β-catenin activation during anagen induction is unknown. In this study, we genetically deleted Wntless (Wls), a gene required for Wnt ligand secretion by Wnt-producing cells, specifically in the hair follicle epithelium during telogen phase. We show that epithelial Wnt ligands are required for anagen, as loss of Wls in the follicular epithelium resulted in a profound hair cycle arrest. Both the follicular epithelium and dermal papilla showed markedly decreased Wnt/β-catenin signaling during anagen induction compared with control hair follicles. Surprisingly, hair follicle stem cells that are responsible for hair regeneration maintained expression of stem cell markers but exhibited significantly reduced proliferation. Finally, we demonstrate that epidermal Wnt ligands are critical for adult wound-induced de novo hair formation. Collectively, these data show that Wnt ligands secreted by the hair follicle epithelium are required for adult hair follicle regeneration and provide new insight into potential cellular targets for the treatment of hair disorders such as alopecia.Journal of Investigative Dermatology advance online publication, 19 July 2012; doi:10.1038/jid.2012.230.
Article
Full-text available
The discovery of long-lived epithelial stem cells in the bulge region of the hair follicle led to the hypothesis that epidermal renewal and epidermal repair after wounding both depend on these cells. To determine whether bulge cells are necessary for epidermal renewal, here we have ablated these cells by targeting them with a suicide gene encoding herpes simplex virus thymidine kinase (HSV-TK) using a Keratin 1-15 (Krt1-15) promoter. We show that ablation leads to complete loss of hair follicles but survival of the epidermis. Through fate-mapping experiments, we find that stem cells in the hair follicle bulge do not normally contribute cells to the epidermis which is organized into epidermal proliferative units, as previously predicted. After epidermal injury, however, cells from the bulge are recruited into the epidermis and migrate in a linear manner toward the center of the wound, ultimately forming a marked radial pattern. Notably, although the bulge-derived cells acquire an epidermal phenotype, most are eliminated from the epidermis over several weeks, indicating that bulge stem cells respond rapidly to epidermal wounding by generating short-lived 'transient amplifying' cells responsible for acute wound repair. Our findings have implications for both gene therapy and developing treatments for wounds because it will be necessary to consider epidermal and hair follicle stem cells as distinct populations.
Article
The adult hair follicle houses stem cells that govern the cyclical growth and differentiation of multiple cell types that collectively produce a pigmented hair. Recent studies have revealed that hair follicle stem cells are heterogeneous and dynamic throughout the hair cycle. Moreover, interactions between heterologous stem cells, including both epithelial and melanocyte stem cells, within the hair follicle are just now being explored. This review will describe how recent findings have expanded our understanding of the development, organization, and regeneration of hair follicle stem cells. At a basic level, this review is intended to help construct a reference point to integrate the surge of studies on the molecular mechanisms that regulate these cells.
Article
Wnt/beta-catenin and NF-kappaB signaling mechanisms provide central controls in development and disease, but how these pathways intersect is unclear. Using hair follicle induction as a model system, we show that patterning of dermal Wnt/beta-catenin signaling requires epithelial beta-catenin activity. We find that Wnt/beta-catenin signaling is absolutely required for NF-kappaB activation, and that Edar is a direct Wnt target gene. Wnt/beta-catenin signaling is initially activated independently of EDA/EDAR/NF-kappaB activity in primary hair follicle primordia. However, Eda/Edar/NF-kappaB signaling is required to refine the pattern of Wnt/beta-catenin activity, and to maintain this activity at later stages of placode development. We show that maintenance of localized expression of Wnt10b and Wnt10a requires NF-kappaB signaling, providing a molecular explanation for the latter observation, and identify Wnt10b as a direct NF-kappaB target. These data reveal a complex interplay and interdependence of Wnt/beta-catenin and EDA/EDAR/NF-kappaB signaling pathways in initiation and maintenance of primary hair follicle placodes.
Article
The mammalian hair follicle is a treasure waiting to be discovered by more molecular geneticists. How can a tiny cluster of apparently uniform epithelial cells, adjacent to a tiny cluster of uniform mesenchymal cells, give rise to five or six concentric cylinders, each of which is composed of cells of a distinctive type that synthesize their own distinctive set of proteins? There is now evidence that several growth factors, cell adhesion molecules and other molecules play important roles in the regulation of this minute organ.
Article
Inconsistent with the view that hair follicle stem cells reside in the matrix area of the hair bulb, we found that label-retaining cells exist exclusively in the bulge area of the mouse hair follicle. The bulge consists of a subpopulation of outer root sheath cells located in the midportion of the follicle at the arrector pili muscle attachment site. Keratinocytes in the bulge area are relatively undifferentiated ultrastructurally. They are normally slow cycling, but can be stimulated to proliferate transiently by TPA. Located in a well-protected and nourished environment, these cells mark the lower end of the "permanent" portion of the follicle. Our findings, plus a reevaluation of the literature, suggest that follicular stem cells reside in the bulge region, instead of the lower bulb. This new view provides insights into hair cycle control and the possible involvement of hair follicle stem cells in skin carcinogenesis.
Article
The opening of intracellular potassium channels is a common mechanism of action for a set of anti-hypertensive drugs that includes the hair-growth-inducing agent minoxidil. Recent work suggests potassium channel openers (PCOs) also influence hair growth. Correlative studies demonstrate that a series of PCOs including minoxidil, pinacidil, P-1075, an active pinacidil analog, RP-49,356, cromakalim, and nicorandil maintain hair growth in cultured vibrissa follicles. Studies using balding stumptail macaques verify that minoxidil, P-1075, and cromakalim but not RP-49,356 stimulate hair growth. The definition of potassium channels and documentation of drug effects on these channels is classically done using electrophysiologic techniques. Such studies require the identification and isolation of target cells. Both these are among the unsolved problems in the area of hair biology. Estimating K+ flux using 86Rb+ as a K+ tracer is an accepted method of assessing potassium channel conductance in other organ systems. Both pinacidil and RP-49,356 induce measurable Rb+ flux in isolated vibrissa follicles and a hair epithelial cell line whereas neither minoxidil nor minoxidil sulfate had measurable effects. Potassium channels have been studied successfully in other organ systems using specific pharmacologic blockers for the various channel subtypes. Blockers including glyburide, tetraethylammonium, and procaine failed to inhibit minoxidil stimulation of cultured follicles. The current explosion of knowledge on potassium channel biology, cloning of channels, and continued progress in hair biology promise to clarify the role of K+ ions in the control of hair follicles.
Article
Clinical conditions causing hair loss, such as androgenetic alopecia, alopecia areata, and scarring alopecia, can be psychologically devastating to individuals and are the target of a multimillion dollar pharmaceutical industry. The importance of the hair follicle in skin biology, however, does not rest solely with its ability to produce hair. Hair follicles are self-renewing and contain reservoirs of multipotent stem cells that are capable of regenerating the epidermis and are thought to be utilized in wound healing. Hair follicles are also the sites of origin of many neoplasias, including some basal cell carcinomas and pilomatricoma. These diseases result from inappropriate activation of signaling pathways that regulate hair follicle morphogenesis. Identification of the signaling molecules and pathways operating in developing and postnatal, cycling, hair follicles is therefore vital to our understanding of pathogenic states in the skin and may ultimately permit the development of novel therapies for skin tumors as well as for hair loss disease. The purpose of this review is to summarize recent progress in our understanding of the molecular mechanisms regulating hair follicle formation, and to discuss ways in which this information may eventually be utilized in the clinic.
Article
Minoxidil has been widely used to treat androgenetic alopecia, but little is known about its pharmacological activity or about the identity of its target cells in hair follicles. We hypothesized that minoxidil has direct effects on the proliferation and apoptosis of dermal papilla cells (DPCs) of human hair follicle. To elucidate the mechanism of topical minoxidil action in terms of stimulating hair growth. We evaluated cell proliferations in cultured DPCs by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and measured the expressions of extracellular signal-regulated kinase (ERK), Akt, Bcl-2, and Bax by Western blot. We also measured elongation of hair follicles in organ culture. Minoxidil significantly increased the proliferation of DPCs. The levels of ERK phosphorylation and of phosphorylated Akt increased significantly 1 h post-treatment; percentage increase of ERK phosphorylation was 287% at 0.1 microM and 351% at 1.0 microM of minoxidil, and that of Akt phosphorylation was 168% at 0.1 microM and 257% at 1.0 microM of minoxidil. 1.0 microM of minoxidil increased Bcl-2 expression over 150%, while 1.0 microM of minoxidil decreased Bax expression by more than 50%. Moreover, a significant elongation of individual hair follicles in organ culture was observed after adding minoxidil. Minoxidil promotes the survival of human DPCs by activating both ERK and Akt and by preventing cell death by increasing the ratio of Bcl-2/Bax. We suggest that minoxidil stimulates the growth of human hairs by prolonging anagen through these proliferative and anti-apoptotic effects on DPCs.
Article
The lowermost portion of the resting (telogen) follicle consists of the bulge and secondary hair germ. We previously showed that the progeny of stem cells in the bulge form the lower follicle and hair, but the relationship of the bulge cells with the secondary hair germ cells, which are also involved in the generation of the new hair at the onset of the hair growth cycle (anagen), remains unclear. Here we address whether secondary hair germ cells are derived directly from epithelial stem cells in the adjacent bulge or whether they arise from cells within the lower follicle that survive the degenerative phase of the hair cycle (catagen). We use 5-bromo-2'-deoxyuridine to label bulge cells at anagen onset, and demonstrate that the lowermost portion of the bulge collapses around the hair and forms the secondary hair germ during late catagen. During the first six days of anagen onset bulge cells proliferate and self-renew. Bulge cell proliferation at this time also generates cells that form the future secondary germ. As bulge cells form the secondary germ cells at the end of catagen, they lose expression of a biochemical marker, S100A6. Remarkably, however, following injury of bulge cells by hair depilation, progenitor cells in the secondary hair germ repopulate the bulge and re-express bulge cell markers. These findings support the notion that keratinocytes can "dedifferentiate" to a stem cell state in response to wounding, perhaps related to signals from the stem cell niche. Finally, we also present evidence that quiescent bulge cells undergo apoptosis during follicle remodeling in catagen, indicating that a subpopulation of bulge cells is not permanent.
Article
Substantial progress has been made regarding the elucidation of differentiation processes of the human hair follicle. This review first describes the genomic organization of the human hair keratin gene family and the complex expression characteristics of hair keratins in the hair-forming compartment. Sections describe the role and fate of hair keratins in the diseased hair follicle, particularly hereditary disorders and hair follicle-derived tumors. Also included is a report on the actual state of knowledge concerning the regulation of hair keratin expression. In the second part of this review, essentially the same principles are applied to outline more recent and, thus, occasionally fewer data on specialized epithelial keratins expressed in various tissue constituents of the external sheaths and the companion layer of the follicle. A closing outlook highlights issues that need to be explored further to deepen our insight into the biology and genetics of the hair follicle.
Article
Hair follicle stem cells sustain growth and cycling of the hair follicle and are located in the permanent portion of the follicle known as the bulge. In this issue of the JCI, Ohyama et al. report the characterization of global gene expression patterns of human hair follicle stem cells after their isolation using sophisticated laser capture techniques to microdissect out bulge cells. They discovered a panel of cell surface markers useful for isolating living hair follicle stem cells, a finding with potential therapeutic implications since isolated stem cells in mice can generate new hair follicles when transplanted to other mice. The findings of Ohyama et al. validate the use of the mouse for studying hair follicle biology but also underscore critical differences between mouse and human stem cell markers. In particular, CD34, which delineates hair follicle stem cells in the mouse, is not expressed by human hair follicle stem cells, while CD200 is expressed by stem cells in both species. Ultimately, this information will assist efforts to develop cell-based and cell-targeted treatments for skin disease.
Article
Putative epithelial stem cells were identified in the hair follicle bulge as quiescent "label retaining cells". The study of these cells was hindered until the identification of bulge cell molecular markers, such as CD34 expression and K15 promoter activity. This allowed for the isolation and characterization of bulge cells from mouse follicles. Bulge cells possess stem cell characteristics, including multipotency, high proliferative potential, and their cardinal feature of quiescence. Lineage analysis demonstrated that all epithelial layers within the adult follicle and hair originated from bulge cells. Bulge cells only contribute to the epidermis during wound healing, but after isolation, when combined with neonatal dermal cells, they regenerate new hair follicles, epidermis, and sebaceous glands. Bulge cells maintain their stem cell characteristics after propagation in vitro, thus ultimately they may be useful for tissue engineering applications. Understanding the signals important for directing movement and differentiation of bulge cells into different lineages will be important for developing treatments based on stem cells as well as clarifying their role in skin disease.
Article
Drugs may cause hair loss, stimulate hair growth, or induce changes in the hair shape and color. Drug-induced hair loss is, in most cases, a consequence of a toxic effect of the drug on the hair matrix. Although a large number of drugs have been occasionally reported to produce hair loss, the relationship between drug intake and hair loss has been proven only for a few agents. Type of hair loss (telogen effluvium, anagen effluvium, or both) depends on the drug, its dosage, and patient's susceptibility. Drug-induced hair loss is usually reversible.