Hair

Hair
Name	Hair
Caption	Hair fibers (schematic)
Latin	pilus
System	Integumentary system

Hair Hair is a keratinous filament produced in follicles in the dermis of mammals and present on many human populations. It exhibits variation in color, texture, density, and distribution across individuals and populations, with roles spanning thermoregulation, sensory input, signaling, and culture. Research encompasses molecular biology, genetics, anthropology, medicine, and cosmetology.

Structure and Composition

The shaft and follicle of hair are composed primarily of keratin proteins synthesized by follicular epithelial cells in the bulb, interacting with melanocytes responsible for pigmentation; studies often reference institutions like National Institutes of Health, Harvard University, Massachusetts Institute of Technology, Stanford University for molecular details and protein studies. Structural analyses draw on methods developed at Max Planck Society, Karolinska Institute, Imperial College London, and University of Cambridge while genetic regulation is investigated at centers such as Broad Institute, Cold Spring Harbor Laboratory, and Wellcome Trust Sanger Institute. The follicle includes the medulla, cortex, and cuticle layers; keratin crosslinking involves disulfide bonds characterized by researchers at Rockefeller University, University of Oxford, and Johns Hopkins University. Pigmentation pathways implicate genes characterized through projects led by European Molecular Biology Laboratory, National Human Genome Research Institute, UC Berkeley, and University of Tokyo.

Growth and Life Cycle

Hair growth follows anagen, catagen, and telogen phases; endocrinological control involves androgenic signals elucidated in studies from Mayo Clinic, Cleveland Clinic, University College London, and University of Pennsylvania. Clinical trials reported in journals associated with American Medical Association, New England Journal of Medicine, and institutions like Karolinska Institute and University of California, San Francisco examine interventions that modulate cycle duration. Age-related changes were characterized in longitudinal cohorts from Framingham Heart Study, Baltimore Longitudinal Study of Aging, and research groups at Columbia University, Yale University, and Duke University. Seasonal and nutritional influences are investigated by teams at Wageningen University, University of British Columbia, and Australian National University.

Types and Distribution

Hair types include vellus and terminal varieties with distinct distribution across body regions and populations studied by anthropologists at University of Chicago, University of Oxford, University of Cambridge, and London School of Economics-affiliated demographic research. Population genetics and phenotypic diversity are mapped in projects by 1000 Genomes Project, Human Genome Diversity Project, National Human Genome Research Institute, and universities such as University of California, Los Angeles, University of Michigan, and Australian National University. Dermatological prevalence data are compiled by societies including American Academy of Dermatology, European Academy of Dermatology and Venereology, and International Society of Hair Restoration Surgery. Forensic applications leverage databases developed at FBI, Interpol, and forensic groups at University of Lausanne, University of Bologna, and McGill University.

Functions and Evolutionary Significance

Thermoregulatory, tactile, and social signaling roles are explored in evolutionary biology contexts by researchers at Smithsonian Institution, American Museum of Natural History, Royal Society, and universities including University of Oxford, University of Cambridge, and Princeton University. Comparative studies across mammals are conducted at institutions like San Diego Zoo Global, Max Planck Institute for Evolutionary Anthropology, University of California, Davis, and University of Wisconsin–Madison. Hypotheses about hair reduction in humans and persistence of scalp and pubic coverage are debated in literature involving contributors from Harvard University, Stanford University, Yale University, and University of Copenhagen. Behavioral ecology and sexual selection models referencing work by Charles Darwin are reexamined in modern syntheses from Royal Society Publishing, Proceedings of the National Academy of Sciences, and research groups at University of California, San Diego.

Hair Disorders and Diseases

Common conditions include alopecia areata, androgenetic alopecia, telogen effluvium, and folliculitis; clinical guidelines are issued by World Health Organization, National Health Service (UK), American Academy of Dermatology, and specialty centers at Mayo Clinic, Cleveland Clinic, and Johns Hopkins Hospital. Autoimmune and genetic causes are investigated in laboratories at NIH, Broad Institute, University of Pennsylvania, and University College London. Therapeutic approaches incorporate pharmaceuticals evaluated in trials run by Food and Drug Administration, European Medicines Agency, and companies such as Pfizer, Johnson & Johnson, and Novartis as well as surgical interventions practiced by clinicians affiliated with International Society of Hair Restoration Surgery and major hospitals like Mount Sinai Hospital and Massachusetts General Hospital.

Cultural, Social, and Cosmetic Aspects

Hair styling, grooming, and symbolic practices feature prominently in histories documented by museums and cultural institutions such as Smithsonian Institution, British Museum, Louvre Museum, Museum of Modern Art, and ethnographic research from University of Cape Town, University of Nairobi, University of Delhi, and Peking University. Fashion houses and designers including Chanel, Dior, Gucci, and Vogue (magazine) have influenced trends alongside media institutions like BBC, CNN, New York Times, and The Guardian. Hair care and cosmetic industries are led by corporations such as L'Oréal, Procter & Gamble, Unilever, and Estée Lauder Companies with standards set by organizations like International Organization for Standardization and regulatory bodies including Food and Drug Administration and European Commission. Social movements and politics involving appearance have been addressed in legal and cultural arenas in cases and debates involving institutions like United Nations, European Court of Human Rights, Supreme Court of the United States, and national legislatures in India, France, and South Africa.

Category:Mammalian integumentary system