Human Hair Graying Revisited: Principles, Misconceptions, And Key Research Frontiers

In this study, researchers found that the human hair follicle microbiota vary by anatomical compartment and donor age, with specific microbes like S. epidermidis potentially influencing hair follicle functions, which suggests new avenues for therapeutic targeting.

This ex vivo study reported that melatonin significantly improved certain aging biomarkers in aged human skin, including reduced mTORC1 activity, increased fibrillin-1, and enhanced collagen and elastic fiber organization, though other key biomarkers remained unchanged.

This study observed unexpected heterogeneity among pigment cells in human scalp hair follicles, identifying immature melanocyte populations outside traditional pigment production zones, raising questions about their potential roles beyond melanin synthesis.

In this study with organ-cultured human scalp hair follicles, high mTORC1 activity correlated with gray/white hair and reduced pigmentation, while inhibiting mTORC1 with rapamycin increased hair growth and pigmentation, suggesting mTORC1 inhibition could be a strategy for treating hair depigmentation and loss.

This review highlights the possibility of safely altering hair color through innovative cosmetics by targeting key biological processes in hair follicles, using insights from mammalian pigmentation studies and drug-induced hair color changes as potential pathways.

This article discusses the role of human scalp hair follicles in neurohormone production and their model potential for studying neuroendocrine signaling, reporting no experimental results.

This study used single-cell RNA sequencing to create a detailed atlas of human scalp hair follicles and found that early-stage hair graying involves matrix hair progenitor depletion linked to P53 pathway activation.

This review discusses the molecular mechanisms driving hair follicle degeneration in skin aging and emphasizes the role of the tissue microenvironment on stem cell function, but reports no new research findings.

This study found that premature hair greying may be associated with low serum ferritin and raised anti-TPO levels.

This study found that hair greying is prevalent among adult traders in Lagos, Nigeria, typically onset at age 30, with premature greying considered uncommon.

This review discusses the role of various cells outside the hair follicle in regulating melanocyte stem cells and hair graying, but reports no new clinical results.

This review examines melatonin's potential effects on human skin and hair follicle pigmentation, highlighting the need to confirm findings from cell cultures in physiological tissue contexts.

This study found that human scalp hair follicles can internally operate a Cori cycle, synthesize glycogen in the presence of lactate, and modulate growth through glycogen phosphorylase activity.

This case report describes canities subita, characterized by sudden hair whitening without hair loss, in a patient following a stressful event, suggesting an immune system involvement.

GNPTAB gene is crucial for normal hair color in humans and mice.

This study using a humanized mouse model of androgenetic alopecia suggests that platelet-rich plasma may promote hair regrowth and improve hair characteristics in vivo.

This review discusses the role of telomere length dynamics in hair follicle biology and reports no new clinical findings, emphasizing the need for further research in humans.

This study demonstrates that dermal white adipose tissue regulates human hair growth and pigmentation through hepatocyte growth factor secretion, highlighting potential therapeutic targets for hair-related disorders.

This review summarizes evidence suggesting that smoking is associated with alopecia and premature hair graying, with smokers showing higher prevalence than nonsmokers.

This study found that ATM protein plays a crucial role in protecting human hair follicle melanocytes from oxidative stress, which is linked to the greying of hair.

In this study, premature hair graying in Egyptians was significantly linked to family history, stress, sedentary lifestyle, and low serum ferritin levels, but not to vitamin D deficiency.

This study found that while genetic variants contribute minimally to predicting hair greying in a Polish population, age remains the primary predictor, underscoring the complexity of hair greying as a genetic trait.

This review emphasizes the potential of repurposing topical L-thyroxine for skin ulcers and telogen effluvium and highlights the need for further exploration of its use in dermatology.

Stress can cause hair to turn gray by depleting stem cells.

This review discusses medication-induced gray hair repigmentation, highlighting that certain anti-inflammatory drugs and melanogenesis stimulators can cause diffuse repigmentation, though evidence remains low-quality and these medications are not currently indicated for this purpose.

This study found that a novel peptide, FOL-005, derived from osteopontin, significantly inhibited hair growth in human hair follicles both ex vivo and in vivo, suggesting potential as a treatment for unwanted hair growth.

The researchers reported that Gambogic Amide may prevent hair greying and promote hair growth by maintaining follicle pigmentation in vitro through activation and migration of melanocytes.

This review discusses the changes in hair follicles with aging, particularly graying due to decreased melanocyte activity, and suggests potential for hair repigmentation under certain conditions, but reports no new results.

This study found that white hair fibers have lower lipid content and different water absorption dynamics compared to brown hair fibers, suggesting differences in their barrier functions.

This study found that ultraviolet radiation negatively affects hair follicle functions in human scalp skin, and caffeine application may provide some protective effects against this damage.

This study found that activating the Nrf2 pathway in human mast cells effectively suppresses degranulation and inflammation induced by substance P.

This study found that autophagy plays a novel role in human hair growth, with altered autophagic flux during hair development phases influencing hair follicle behavior in a preclinical model.

This review discusses melatonin's potential in dermatology, highlighting its antioxidative, immunomodulatory, and DNA repair properties, but reports no new clinical results.

This study observed that individuals with premature hair graying had lower levels of certain serum nutrients and lifestyle factors like stress and smoking may contribute; hair oiling appeared protective.

This review examines current understanding of hair graying and suggests it may be caused by depletion of melanocyte stem cells due to genotoxic stress or dysfunctional melanocytes from oxidative stress.

This study visualized mitochondrial metabolism in cultured bovine hair follicles and plucked human hairs, finding that ROS and mitochondrial polarization correlate in specific hair follicle regions, particularly near keratin deposition sites.

This study found that premature hair graying is strongly associated with a family history, Vitamin B12 deficiency, and hypothyroidism, with onset as early as 5 years in patients in Gurugram, India.

This study found that activating Nrf2 in human hair follicles significantly reduced oxidative stress, lipid peroxidation, and protected against hair growth inhibition, suggesting a protective role for Nrf2 against redox insult in this context.

In this study, researchers identified 18 genetic associations with scalp and facial hair traits in Latin Americans, including novel loci for hair greying and balding, with implications for understanding hair evolution.

This research found that Foxc1 transcription factor and COL17A1 are critical in regulating quiescence and hair thinning in hair follicle stem cells, with aging-related DNA damage leading to hair loss.

This review considers oxidative stress effects on hair aging and emphasizes the need for dermatologists to recognize and treat factors affecting scalp and hair health, but it provides no new clinical findings.

This article presents a comprehensive guide for classifying human hair follicle cycle stages in vivo using scalp xenografts on immunocompromised mice, offering valuable resources for researchers in the field.

This review provides a comprehensive guide to serum-free human hair follicle organ culture methods, highlighting research opportunities, standardization efforts, and potential applications without reporting new empirical findings.

This report describes a patient experiencing hair repigmentation linked to adalimumab therapy, a TNF inhibitor, a phenomenon not previously associated with this class of drugs.

This study found that smoking, obesity, and family history are significant risk factors for premature hair graying in young men.

This study found that silencing clock genes BMAL1 or PER1 in human hair follicles increased melanin content and melanocyte activity, suggesting these genes influence pigmentation.

This article discusses the role of human hair follicles in neuroendocrinology and suggests potential new therapeutic targets by examining how neuromediators influence hair growth, pigmentation, and stem cell biology in organ cultures.

This study found that compromised antioxidant activity in gray hair follicles affects both mature melanocytes and their immature precursors, linked to down-regulation of melanogenesis-related genes.

This case report describes repigmentation and curling of hair in a patient undergoing acitretin therapy.

This study found that peripheral clock genes, particularly BMAL1 and Period1, modulate human hair follicle cycling, suggesting their potential as therapeutic targets for affecting hair growth.

This review discusses the role of oxidative stress in hair greying and suggests that understanding melanocyte susceptibility at different follicular locations may help develop therapies for preventing and reversing the process; it reports no new experimental results.

HPT axis hormones boost mitochondrial function and growth in hair follicles, potentially aiding hair health.

This review discusses various genetic and acquired conditions associated with poliosis circumscripta and reports no new clinical results.

In this study, silencing P-cadherin in human scalp hair follicles reduced melanogenesis and associated protein expression, suggesting P-cadherin is crucial for normal hair pigmentation via GSK3β-mediated Wnt signaling.

In this study, knockout of B-raf and C-raf genes in mice showed they are not needed for early melanocyte development, but are crucial for maintaining melanocyte stem cells, as evidenced by hair graying due to stem cell depletion.

This study found that non-pigmented hair follicles have significantly lower expression of nucleotide excision repair genes, which may be associated with reduced melanin production capacity in these follicles.

Alopecia Areata is an autoimmune condition causing hair loss with no cure and treatments that often don't work well.

This case report describes an elderly multiple myeloma patient whose hair repigmentation was associated with lenalidomide use, suggesting hair graying may be reversible.

This study reveals that human hair follicles transition between active and dormant states stochastically, challenging the idea of a cyclical automaton controlling hair growth.

This study found that activation of cannabinoid 1 receptors in human scalp hair follicles may limit excessive mast cell activation and maturation, suggesting a potential therapeutic strategy for managing MC-dependent skin diseases.

This study found that white hair exhibits increased expression of genes and proteins linked to active hair growth compared to black hair, suggesting that hair greying is associated with enhanced hair growth activity.

This study found that Wnt signaling in the hair follicle is crucial for coordinating the behavior of epithelial and melanocyte stem cells, which drives hair regeneration and melanocyte differentiation in mice.

This review discusses the identification and characteristics of melanocyte stem cells, emphasizing their role in hair pigmentation, greying, and skin repigmentation, but reports no new research findings.

COL17A1 is crucial for preventing hair graying and loss by supporting hair and pigment stem cells.

This study suggests that the susceptibility of hair follicle melanocytes to oxidative stress as they age may be key in the graying of hair due to reduced catalase expression and activity.

This letter reports repigmentation of hair in patients receiving latanoprost therapy.

This article discusses the role of neurohormones and neuropeptides in hair follicle pigmentation and outlines promising neuroendocrinological strategies to address greying and damage, but reports no new clinical results.

This article discusses the challenges in hair follicle pigmentation research compared to epidermal melanocytes and highlights the limitations of relying on mouse models, but reports no new experimental findings.

This study found that both genetic and environmental factors influence appearance-related aging in women, with skin wrinkling, hair graying, and sun damage significantly affecting perceived age more than chronological age.

This study found that thyrotropin-releasing hormone (TRH) acts as a potent stimulator of hair growth in human scalp hair follicles, promoting elongation and prolonging the anagen phase.

This research highlights that psychological stress can adversely affect hair growth in mice, implicating potential pathways that may be relevant in understanding stress-induced hair growth inhibition in humans.

This review observes that trichomegaly, a newly described side effect of EGFR inhibitors causing excessive eyelash and scalp hair growth, persists in some patients whose tumors respond positively to the therapy.

This study found that hydrogen peroxide accumulation and reduced methionine sulfoxide repair play a significant role in the oxidative damage linked to senile hair graying.

This review summarizes fundamental concepts and recent advancements in hair follicle biology, including insights from mouse models into broader molecular and cellular processes relevant to regeneration and development.

In this study, UVB irradiation of organ-cultured human anagen hair follicles in vitro reduced hair elongation and increased cell death, affecting hair growth and regulatory processes.

This review examines the differential aging of melanocytes in hair follicles and skin, and reports no new findings; the authors suggest further research is needed to understand these processes.

In this study, T3 and T4 were found to directly influence human hair follicles in vitro, enhancing keratinocyte proliferation, prolonging the hair growth phase, and affecting pigmentation.

This study found that in androgenetic alopecia, reduced stem cell factor production by dermal papilla cells may lead to decreased pigmentation in hair follicles.

In this study, researchers found that substance P triggered premature catagen development and immune changes in human scalp hair follicles, providing a possible biological link between stress and hair loss conditions like telogen effluvium and alopecia areata.

This study suggests that topical T3 can induce hair follicles to enter the growth phase and may reverse graying in mice, with in vitro results supporting enhanced hair shaft growth.

This study suggests that melatonin plays a role in hair follicle function by modulating growth and pigmentation, and it may act as a protective agent in active hair growth phases.

This study found that organ-cultured human scalp hair follicles can mimic chemotherapy-induced damage in vivo and serve as a model to explore molecular targets and protective agents for hair follicle preservation.

This study found that deleting the ATR gene in adult mice led to rapid onset of age-related traits such as hair graying and osteoporosis through reduced regenerative capacity.

This study found that oxidative stress in hair follicle melanocytes contributes to premature aging and apoptosis, providing insights into graying as a model for studying aging and testing antiaging therapies.

This study provides evidence that psychoemotional stress inhibits hair growth in mice by affecting the brain-hair follicle axis, with specific neuropeptides and treatments modulating this effect.

This study suggests that different melanocyte subpopulations in hair follicles have varying patterns of apoptosis and survival during the catagen phase, which may inform models for modulating melanocyte behavior in vivo.

This review discusses how the CRH/POMC systems may regulate human hair follicle pigmentation and highlights the concept of "self-similarity" in melanocortin systems at both local and systemic levels, without presenting new experimental results.

This study found that hair follicles in both mice and humans may serve as an important site for melatonin synthesis and signaling, potentially influencing hair cycle regulation by modulating keratinocyte apoptosis.

This review discusses the cutaneous serotoninergic/melatoninergic system's potential role in skin function and resilience against environmental and internal stresses, but does not report new experimental findings.

This article reviews follicular melanogenesis, detailing how melanin synthesis and its regulation in hair follicles depend on a complex interplay of cellular and molecular mechanisms, but reports no new clinical findings.

In this study, a superoxide dismutase gel prevented hair graying in mice exposed to photosensitization, suggesting that antioxidants can protect against oxidative damage involved in hair aging.

This study found that thyroid-stimulating hormone receptors are functionally expressed in various skin cells, implying potential physiological and pathological roles in skin, especially in conditions like autoimmune diseases.

This report describes two cases of sustained hair repigmentation related to porphyria cutanea tarda, though the underlying mechanism remains unclear.

This study found that VEGF significantly enhances perifollicular vascularization during the hair growth phase, accelerating hair regrowth and increasing follicle and hair size, while its inhibition retards hair growth.

This study observed that melanogenesis in human hair follicles is linked to anagen phases, with melanocyte activity and enzyme expression being region-specific to the nascent bulb.

This article discusses the biologic and psychosocial significance of hair, the current limitations in hair growth drugs, and anticipates future therapies based on advancing hair follicle research.

In this study, different types of catagen in the C57BL/6 mouse model exhibited varying effects on hair follicle melanocytes and melanin distribution, with spontaneous and dexamethasone-induced catagen showing pigment incontinence, while cyclophosphamide-induced catagen retained dendritic melanocytes but increased ectopic melanin.

This study found that the switch-off of melanogenesis during the hair cycle in C57 BL-6 mice is a gradual and stochastic process starting in mid anagen VI, with specific biochemical markers indicating the transition to catagen.

This review discusses the role of intrinsic skin signals, rather than serum signals, in regulating melanin synthesis and hair pigmentation, but reports no new experimental data.

This study observed that oral calcium pantothenate may reverse hair greying in some adolescent cases, as seen in two girls whose grey hairs turned black after treatment.