hair hair hair is a protein filament that grows from follicles found in the dermis. hair is one of the defining characteristics of mammals. the human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fine vellus hair. most common interest in hair is focused on hair growth, hair types, and hair care, but hair is also an important biomaterial primarily composed of protein, notably alpha-keratin. haircross section of a hair strandscanning electron microscopy image of merino wool (top) and human hair (bottom) showing keratin scalesdetailssystemintegumentary systemidentifierslatincapillummeshd006197ta98a16.0.00.014ta27053thh3.12.00.3.02001 fma53667anatomical terminology attitudes towards different forms of hair, such as hairstyles and hair removal, vary widely across different cultures and historical periods, but it is often used to indicate a person's personal beliefs or social position, such as their age, sex, or religion. overview anatomy of the hair shaft and bulb. the word "hair" usually refers to two distinct structures: the part beneath the skin, called the hair follicle, or, when pulled from the skin, the bulb or root. this organ is located in the dermis and maintains stem cells, which not only re-grow the hair after it falls out, but also are recruited to regrow skin after a wound. the hair shaft, which is the hard filamentous part that extends above the skin surface. a cross section of the hair shaft may be divided roughly into three zones. hair fibers have a structure consisting of several layers, starting from the outside: the cuticle, which consists of several layers of flat, thin cells laid out overlapping one another as roof shingles the cortex, which contains the keratin bundles in cell structures that remain roughly rod-like the medulla, a disorganized and open area at the fiber's center description hair follicle of felidae. each strand of hair is made up of the medulla, cortex, and cuticle. the innermost region, the medulla, is an open and unstructured region which is not always present. the highly structural and organized cortex, or second of three layers of the hair, is the primary source of mechanical strength and water uptake. the cortex contains melanin, which colors the fiber based on the number, distribution and types of melanin granules. the melanin may be evenly spaced or cluster around the edges of the hair. the shape of the follicle determines the shape of the cortex, and the shape of the fiber is related to how straight or curly the hair is. people with straight hair have round hair fibers. oval and other shaped fibers are generally more wavy or curly. the cuticle is the outer covering. its complex structure slides as the hair swells and is covered with a single molecular layer of lipid that makes the hair repel water. the diameter of human hair varies from 0.017 to 0.18 millimeters (0.00067 to 0.00709 in). some of these characteristics in humans' head hair vary by race: people of mostly african ancestry tend to have hair with a diameter of 60-90 μm and a flat cross-section, while people of mostly european or middle eastern ancestry tend to have hair with a diameter of 70-100 μm and an oval cross-section, and people of mostly asian or native american ancestry tend to have hair with a diameter of 90-120 μm and a round cross-section. there are roughly two million small, tubular glands and sweat glands that produce watery fluids that cool the body by evaporation. the glands at the opening of the hair produce a fatty secretion that lubricates the hair. hair growth begins inside the hair follicle. the only "living" portion of the hair is found in the follicle. the hair that is visible is the hair shaft, which exhibits no biochemical activity and is considered "dead". the base of a hair's root (the "bulb") contains the cells that produce the hair shaft. other structures of the hair follicle include the oil producing sebaceous gland which lubricates the hair and the arrector pili muscles, which are responsible for causing hairs to stand up. in humans with little body hair, the effect results in goose bumps. root of the hair root of the hairsection of skin, showing the epidermis and dermis; a hair in its follicle; the arrector pili muscle; sebaceous glands.detailsidentifierslatinradix pilimeshd006197ta98a16.0.00.014ta27053thh3.12.00.3.02001 fma53667anatomical terminology the root of the hair ends in an enlargement, the hair bulb, which is whiter in color and softer in texture than the shaft and is lodged in a follicular involution of the epidermis called the hair follicle. the bulb of hair consists of fibrous connective tissue, glassy membrane, external root sheath, internal root sheath composed of epithelium stratum (henle's layer) and granular stratum (huxley's layer), cuticle, cortex and medulla. natural color human hair contains melanin which provides dark coloration and protection from uv radiation. human hair can absorb and emit light across a wide range of wavelengths. the image above depicts melanin autofluorescence at 365-400 nm excitation from a strand of dark brown human hair. a woman with dark blonde hair. the basal color appears brown due to higher levels of brownish eumelanin. all natural hair colors are the result of two types of hair pigments. both of these pigments are melanin types, produced inside the hair follicle and packed into granules found in the fibers. eumelanin is the dominant pigment in brown hair and black hair, while pheomelanin is dominant in red hair. blond hair is the result of having little pigmentation in the hair strand. gray hair occurs when melanin production decreases or stops, while poliosis is white hair (and often the skin to which the hair is attached), typically in spots that never possessed melanin at all, or ceased for natural reasons, generally genetic, in the first years of life. human hair growth main article: human hair growth hair grows everywhere on the external body except for mucus membranes and glabrous skin, such as that found on the palms of the hands, soles of the feet, and lips. hair follows a specific growth cycle with three distinct and concurrent phases: anagen, catagen, and telogen phases; all three occur simultaneously throughout the body. each has specific characteristics that determine the length of the hair. the body has different types of hair, including vellus hair and androgenic hair, each with its own type of cellular construction. the different construction gives the hair unique characteristics, serving specific purposes, mainly, warmth and protection. texture hair type 4c hair exists in a variety of textures. three main aspects of hair texture are the curl pattern, volume, and consistency. all mammalian hair is composed of keratin, so the make-up of hair follicles is not the source of varying hair patterns. there are a range of theories pertaining to the curl patterns of hair. scientists have come to believe that the shape of the hair shaft has an effect on the curliness of the individual's hair. a very round shaft allows for fewer disulfide bonds to be present in the hair strand. this means the bonds present are directly in line with one another, resulting in straight hair. the flatter the hair shaft becomes, the curlier hair gets, because the shape allows more cysteines to become compacted together resulting in a bent shape that, with every additional disulfide bond, becomes curlier in form. as the hair follicle shape determines curl pattern, the hair follicle size determines thickness. while the circumference of the hair follicle expands, so does the thickness of the hair follicle. an individual's hair volume, as a result, can be thin, normal, or thick. the consistency of hair can almost always be grouped into three categories: fine, medium, and coarse. this trait is determined by the hair follicle volume and the condition of the strand. fine hair has the smallest circumference, coarse hair has the largest circumference, and medium hair is anywhere between the other two. coarse hair has a more open cuticle than thin or medium hair causing it to be the most porous. classification systems there are various systems that people use to classify their curl patterns. being knowledgeable of an individual's hair type is a good start to knowing how to take care of one's hair. there is not just one method to discovering one's hair type. additionally it is possible, and quite normal to have more than one kind of hair type, for instance having a mixture of both type 3a & 3b curls. andre walker system the andre walker hair typing system is the most widely used system to classify hair. the system was created by the hairstylist of oprah winfrey, andre walker. according to this system there are four types of hair: straight, wavy, curly, kinky. type 1 is straight hair, which reflects the most sheen and also the most resilient hair of all of the hair types. it is hard to damage and immensely difficult to curl this hair texture. because the sebum easily spreads from the scalp to the ends without curls or kinks to interrupt its path, it is the most oily hair texture of all. type 2 is wavy hair, whose texture and sheen ranges somewhere between straight and curly hair. wavy hair is also more likely to become frizzy than straight hair. while type a waves can easily alternate between straight and curly styles, type b and c wavy hair is resistant to styling. type 3 is curly hair known to have an s-shape. the curl pattern may resemble a lowercase "s", uppercase "s", or sometimes an uppercase "z" or lowercase "z". lack of proper care causes less defined curls. type 4 is kinky hair, which features a tightly coiled curl pattern (or no discernible curl pattern at all) that is often fragile with a very high density. this type of hair shrinks when wet and because it has fewer cuticle layers than other hair types it is more susceptible to damage. andre walker hair types type 1: straight 1a straight (fine/thin) hair tends to be very soft, thin, shiny, oily, poor at holding curls, difficult to damage. 1b straight (medium) hair characterized by volume and body. 1c straight (coarse) hair tends to be bone-straight, coarse, difficult to curl. type 2: wavy 2a wavy (fine/thin) hair has definite "s" pattern, can easily be straightened or curled, usually receptive to a variety of styles. 2b wavy (medium) can tend to be frizzy and a little resistant to styling. 2c wavy (coarse) fairly coarse, frizzy or very frizzy with thicker waves, often more resistant to styling. type 3: curly 3a curly (loose) presents a definite "s" pattern, tends to combine thickness, volume, and/or frizziness. 3b curly (tight) presents a definite "s" pattern, curls ranging from spirals to spiral-shaped corkscrew type 4: kinky 4a kinky (soft) hair tends to be very wiry and fragile, tightly coiled and can feature curly patterning. 4b kinky (wiry) as 4a but with less defined pattern of curls, looks more like a "z" with sharp angles fia system this is a method which classifies the hair by curl pattern, hair-strand thickness and overall hair volume. fia hair classification curliness straight 1a stick-straight. 1b straight but with a slight body wave adding some volume. 1c straight with body wave and one or two visible s-waves (e.g. at nape of neck or temples). wavy 2a loose with stretched s-waves throughout. 2b shorter with more distinct s-waves (resembling e.g. braided damp hair). 2c distinct s-waves, some spiral curling. curly 3a big, loose spiral curls. 3b bouncy ringlets. 3c tight corkscrews. very ("really") curly 4a tightly coiled s-curls. 4b z-patterned (tightly coiled, sharply angled) 4c mostly z-patterned (tightly kinked, less definition) strands f fine thin strands that sometimes are almost translucent when held up to the light. shed strands can be hard to see even against a contrasting background. fine hair is difficult to feel or it feels like an ultra-fine strand of silk. m medium strands are neither fine nor coarse. medium hair feels like a cotton thread, but isn't stiff or rough. it is neither fine nor coarse. c coarse thick strands whose shed strands usually are easily identified. coarse hair feels hard and wiry. volumeby circumference of full-hair ponytail i thincircumference less than 2 inches (5 centimetres) ii normal... from 2 to 4 inches (5 to 10 centimetres) iii thick... more than 4 inches (10 centimetres) composition hair is