Haira filamentous, often pigmented, outgrowth from the skinis found only on mammals and often in a high-density of filaments per unit area. These threadlike fibers protrude from the outer naked old women with gray hair
of the skin, the epidermisand grow from hair follicles in the inner portion of the skin, the dermis. Each fiber comprises nonliving cells whose primary component is long chains polymers of amino acids forming the protein keratin. The keratinized cells arise from cell division in the hair naked old women with gray hair
at the base of a hair follicle and are tightly packed together. Keratins also are a principle part of the cells in the nails, feathershooves, horny tissues, and tooth enamel of mammals.