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.

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.[1]

Hair
Gray945
Cross section of a hair strand
CSIRO ScienceImage 8115 Human hair and Merino wool fibre
Scanning electron microscopy image of Merino wool (top) and human hair (bottom) showing keratin scales.
Details
SystemIntegumentary system
Identifiers
Latincapillum
MeSHD006197
TAA16.0.00.014
THH3.12.00.3.02001
FMA70752
Anatomical terminology

Overview

The word "hair" usually refers to two distinct structures:

  1. the part beneath the skin, called the hair follicle, or, when pulled from the skin, the bulb. 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.[2]
  2. the 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:

  1. the cuticle, which consists of several layers of flat, thin cells laid out overlapping one another as roof shingles
  2. the cortex, which contains the keratin bundles in cell structures that remain roughly rod-like
  3. the medulla, a disorganized and open area at the fiber's center[3]

Description

Each strand of hair is made up of the medulla, cortex, and cuticle.[4] The innermost region, the medulla, is not always present and is an open, unstructured region.[5] 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 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.[4] The diameter of human hair varies from 0.017 to 0.18 millimeters (0.00067 to 0.00709 in).[6] There are 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.[7]

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.[8] 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 hair
Gray944
Section of skin, showing the epidermis and dermis; a hair in its follicle; the Arrector pili muscle; sebaceous glands.
Details
Identifiers
Latinradix pili
MeSHD006197
TAA16.0.00.014
THH3.12.00.3.02001
FMA70752
Anatomical 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.[9]

Natural color

Brown 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 hair (and often the skin to which the hair is attached), typically in spots, that never possessed melanin at all in the first place, or ceased for natural genetic reasons, generally, in the first years of life.

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 - while one strand of hair may be in the anagen phase, another may be in the telogen phase. 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

OrangeCat hair
Orange American shorthair cat.

Hair exists in a variety of textures. Three main aspects of hair texture are the curl pattern, volume, and consistency. The derivations of hair texture are not fully understood. 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.[10]

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.[10] 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.[11] Fine hair has the smallest circumference, coarse hair has the largest circumference, and medium hair is anywhere between the other two.[11] Coarse hair has a more open cuticle than thin or medium hair causing it to be the most porous.[11]

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". This hair type is usually voluminous, "climate dependent (humidity = frizz), and damage-prone." 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, shiny, oily and poor at holding curls, but difficult to damage. 
1b Straight (Medium) Hair characterised by volume and body.
1c Straight (Coarse) Hair tends to be bone-straight and difficult to curl. Common in Asian women.
TYPE 2: Wavy
2a Wavy (Fine/Thin) Hair has definite "S" pattern and is usually receptive to a variety of styles.
2b Wavy (Medium) Can tend to be frizzy and a little resistant to styling.
2c Wavy (Coarse) Frizzy or very frizzy with thicker waves; often more resistant to styling.
TYPE 3: Curly
3a Curly (Loose) Curly hair that usually presents a definite "S" pattern and tends to combine thickness, fullness, body and/or frizziness. 
3b Curly (Tight) As 3a but with tighter curling like a spiral.
TYPE 4: Kinky
4a Kinky (Soft) Hair tends to be very fragile, tightly coiled and can feature curly patterning.
4b Kinky (Wiry) As 4a but with less visible (or no) curly patterning.
4c Kinky (Wiry) As 4a and 4b but with almost no defined curl pattern.
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; similar to hair found on many people of
Scandinavian descent. You can also try rolling a strand between your thumb and index finger.
Fine hair is difficult to feel or it feels like an ultra-fine strand of silk.

M Medium

Strands are neither fine nor coarse; similar to hair found on many Caucasians. You can also try
rolling a strand between your thumb and index finger. Medium hair feels like a cotton thread.
You can feel it, but it isn't stiff or rough. It is neither fine nor coarse.

C Coarse

Thick strands whose shed strands usually are easily identified against most backgrounds;
similar to hair found on many people of Asian or Native American descent. You can also try
rolling a strand between your thumb and index finger. Coarse hair feels hard and wiry.
As you roll it back and forth, you may hear it.

Volume
by circumference of full-hair ponytail
i Thin circumference 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)

Functions

Many mammals have fur and other hairs that serve different functions. Hair provides thermal regulation and camouflage for many animals; for others it provides signals to other animals such as warnings, mating, or other communicative displays; and for some animals hair provides defensive functions and, rarely, even offensive protection. Hair also has a sensory function, extending the sense of touch beyond the surface of the skin. Guard hairs give warnings that may trigger a recoiling reaction.

Warmth

Ursus maritimus Steve Amstrup
Polar bears use their fur for warmth and while their skin is black, their transparent fur appears white and provides camouflage while hunting and serves as protection by hiding cubs in the snow.

While humans have developed clothing and other means of keeping warm, the hair found on the head serves primarily as a source of heat insulation and cooling (when sweat evaporates from soaked hair) as well as protection from ultra-violet radiation exposure. The function of hair in other locations is debated. Hats and coats are still required while doing outdoor activities in cold weather to prevent frostbite and hypothermia, but the hair on the human body does help to keep the internal temperature regulated. When the body is too cold, the arrector pili muscles found attached to hair follicles stand up, causing the hair in these follicles to do the same. These hairs then form a heat-trapping layer above the epidermis. This process is formally called piloerection, derived from the Latin words 'pilus' ('hair') and 'erectio' ('rising up'), but is more commonly known as 'having goose bumps' in English.[12] This is more effective in other mammals whose fur fluffs up to create air pockets between hairs that insulate the body from the cold. The opposite actions occur when the body is too warm; the arrector muscles make the hair lie flat on the skin which allows heat to leave.

Protection

In some mammals, such as hedgehogs and porcupines, the hairs have been modified into hard spines or quills. These are covered with thick plates of keratin and serve as protection against predators. Thick hair such as that of the lion's mane and grizzly bear's fur do offer some protection from physical damages such as bites and scratches.

Touch sense

Displacement and vibration of hair shafts are detected by hair follicle nerve receptors and nerve receptors within the skin. Hairs can sense movements of air as well as touch by physical objects and they provide sensory awareness of the presence of ectoparasites.[13] Some hairs, such as eyelashes, are especially sensitive to the presence of potentially harmful matter.[14][15][16][17]

Eyebrows and eyelashes

Eyelashes
Eyelashes and eyebrows help to protect the eyes from dust, dirt, and sweat.

The eyebrows provide moderate protection to the eyes from dirt, sweat and rain. They also play a key role in non-verbal communication by displaying emotions such as sadness, anger, surprise and excitement. In many other mammals, they contain much longer, whisker-like hairs that act as tactile sensors.

The eyelash grows at the edges of the eyelid and protects the eye from dirt. The eyelash is to humans, camels, horses, ostriches etc., what whiskers are to cats; they are used to sense when dirt, dust, or any other potentially harmful object is too close to the eye.[18] The eye reflexively closes as a result of this sensation.

Evolution

Hair has its origins in the common ancestor of mammals, the synapsids, about 300 million years ago. It is currently unknown at what stage the synapsids acquired mammalian characteristics such as body hair and mammary glands, as the fossils only rarely provide direct evidence for soft tissues. Skin impression of the belly and lower tail of a pelycosaur, possibly Haptodus shows the basal synapsid stock bore transverse rows of rectangular scutes, similar to those of a modern crocodile.[19] An exceptionally well-preserved skull of Estemmenosuchus, a therapsid from the Upper Permian, shows smooth, hairless skin with what appears to be glandular depressions,[20] though as a semi-aquatic species it might not have been particularly useful to determine the integument of terrestrial species. The oldest undisputed known fossils showing unambiguous imprints of hair are the Callovian (late middle Jurassic) Castorocauda and several contemporary haramiyidans, both near-mammal cynodonts.[21][22][23] More recently, studies on terminal Permian Russian coprolites may suggest that non-mammalian synapsids from that era had fur.[24] If this is the case, these are the oldest hair remnants known, showcasing that fur occurred as far back as the latest Paleozoic.

Some modern mammals have a special gland in front of each orbit used to preen the fur, called the harderian gland. Imprints of this structure are found in the skull of the small early mammals like Morganucodon, but not in their cynodont ancestors like Thrinaxodon.[25]

The hairs of the fur in modern animals are all connected to nerves, and so the fur also serves as a transmitter for sensory input. Fur could have evolved from sensory hair (whiskers). The signals from this sensory apparatus is interpreted in the neocortex, a chapter of the brain that expanded markedly in animals like Morganucodon and Hadrocodium.[26] The more advanced therapsids could have had a combination of naked skin, whiskers, and scutes. A full pelage likely did not evolve until the therapsid-mammal transition.[27] The more advanced, smaller therapsids could have had a combination of hair and scutes, a combination still found in some modern mammals, such as rodents and the opossum.[28]

The high interspecific variability of the size, color, and microstructure of hair often enables the identification of species based on single hair filaments.[29][30]

Nacktmull
Naked mole-rat (Heterocephalus glaber) in a zoo.

In varying degrees most mammals have some skin areas without natural hair. On the human body, glabrous skin is found on the ventral portion of the fingers, palms, soles of feet and lips, which are all parts of the body most closely associated with interacting with the world around us,[31] as are the labia minora and glans penis.[32] There are four main types of mechanoreceptors in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini corpuscles.

The naked mole-rat (Heterocephalus glaber) has evolved skin lacking in general, pelagic hair covering, yet has retained long, very sparsely scattered tactile hairs over its body.[31] Glabrousness is a trait that may be associated with neoteny.[33]

Human hairlessness

The general hairlessness of humans in comparison to related species may be due to loss of functionality in the pseudogene KRTHAP1 (which helps produce keratin) in the human lineage about 240,000 years ago.[34] On an individual basis, mutations in the gene HR can lead to complete hair loss, though this is not typical in humans.[35] Humans may also lose their hair as a result of hormonal imbalance due to drugs or pregnancy.[36]

In order to comprehend why humans are essentially hairless, it is essential to understand that mammalian body hair is not merely an aesthetic characteristic; it protects the skin from wounds, bites, heat, cold, and UV radiation.[37] Additionally, it can be used as a communication tool and as a camouflage.[38] To this end, it can be concluded that benefits stemming from the loss of human body hair must be great enough to outweigh the loss of these protective functions by nakedness.

Humans are the only primate species that have undergone significant hair loss and of the approximately 5000 extant species of mammal, only a handful are effectively hairless. This list includes elephants, rhinoceroses, hippopotamuses, walruses, some species of pigs, whales and other cetaceans, and naked mole rats.[38] Most mammals have light skin that is covered by fur, and biologists believe that early human ancestors started out this way also. Dark skin probably evolved after humans lost their body fur, because the naked skin was vulnerable to the strong UV radiation as explained in the Out of Africa hypothesis. Therefore, evidence of the time when human skin darkened has been used to date the loss of human body hair, assuming that the dark skin was needed after the fur was gone. It was expected that dating the split of the ancestral human louse into two species, the head louse and the pubic louse, would date the loss of body hair in human ancestors. However, it turned out that the human pubic louse does not descend from the ancestral human louse, but from the gorilla louse, diverging 3.3 million years ago. This suggests that humans had lost body hair (but retained head hair) and developed thick pubic hair prior to this date, were living in or close to the forest where gorillas lived, and acquired pubic lice from butchering gorillas or sleeping in their nests.[39][40] The evolution of the body louse from the head louse, on the other hand, places the date of clothing much later, some 100,000 years ago.[41][42]

Vulpes vulpes sitting
The soft, fine hair found on many nonhuman mammals is typically called fur.[43]

The sweat glands in humans could have evolved to spread from the hands and feet as the body hair changed, or the hair change could have occurred to facilitate sweating. Horses and humans are two of the few animals capable of sweating on most of their body, yet horses are larger and still have fully developed fur. In humans, the skin hairs lie flat in hot conditions, as the arrector pili muscles relax, preventing heat from being trapped by a layer of still air between the hairs, and increasing heat loss by convection.

Another hypothesis for the thick body hair on humans proposes that Fisherian runaway sexual selection played a role (as well as in the selection of long head hair), (see types of hair and vellus hair), as well as a much larger role of testosterone in men. Sexual selection is the only theory thus far that explains the sexual dimorphism seen in the hair patterns of men and women. On average, men have more body hair than women. Males have more terminal hair, especially on the face, chest, abdomen, and back, and females have more vellus hair, which is less visible. The halting of hair development at a juvenile stage, vellus hair, would also be consistent with the neoteny evident in humans, especially in females, and thus they could have occurred at the same time.[44] This theory, however, has significant holdings in today's cultural norms. There is no evidence that sexual selection would proceed to such a drastic extent over a million years ago when a full, lush coat of hair would most likely indicate health and would therefore be more likely to be selected for, not against, and not all human populations today have sexual dimorphism in body hair.

A further hypothesis is that human hair was reduced in response to ectoparasites.[45][46] The "ectoparasite" explanation of modern human nakedness is based on the principle that a hairless primate would harbor fewer parasites. When our ancestors adopted group-dwelling social arrangements roughly 1.8 mya, ectoparasite loads increased dramatically. Early humans became the only one of the 193 primate species to have fleas, which can be attributed to the close living arrangements of large groups of individuals. While primate species have communal sleeping arrangements, these groups are always on the move and thus are less likely to harbor ectoparasites. Because of this, selection pressure for early humans would favor decreasing body hair because those with thick coats would have more lethal-disease-carrying ectoparasites and would thereby have lower fitness.

Another view is proposed by James Giles, who attempts to explain hairlessness as evolved from the relationship between mother and child, and as a consequence of bipedalism. Giles also connects romantic love to hairlessness.[47]

Another hypothesis is that humans' use of fire caused or initiated the reduction in human hair.[48]

Evolutionary variation

Evolutionary biologists suggest that the genus Homo arose in East Africa approximately 2.5 million years ago.[49] They devised new hunting techniques.[49] The higher protein diet led to the evolution of larger body and brain sizes.[49] Jablonski[49] postulates that increasing body size, in conjunction with intensified hunting during the day at the equator, gave rise to a greater need to rapidly expel heat. As a result, humans evolved the ability to sweat: a process which was facilitated by the loss of body hair.[49] A major problem with this theory, however, is that it does not explain why males are larger, hairier, and were more active in hunting than females. The female-male size differential among other closely associated primates is much greater than among humans, and therefore it was reduced during human evolution. Other primates have sweat gland in their armpits that function as those of humans, and thus it is probable that human sweat glands evolved from a similar distribution, spreading to more areas of the body, rather than occurring through evolution of a new trait. It is not known whether the increased distribution of sweat glands occurred before, during, or after, the change in body hair, or even whether the two are related developments. Horses also sweat, and they are larger, hairier, and expend more energy running than human males, so there may not be any connection between the ability to sweat and the apparent hairlessness of humans.

Another factor in human evolution that also occurred in the prehistoric past was a preferential selection for neoteny, particularly in females. The idea that adult humans exhibit certain neotenous (juvenile) features, not evinced in the great apes, is about a century old. Louis Bolk made a long list of such traits,[50] and Stephen Jay Gould published a short list in Ontogeny and Phylogeny.[51] In addition, paedomorphic characteristics in women are often acknowledged as desirable by men in developed countries.[52] For instance, vellus hair is a juvenile characteristic. However, while men develop longer, coarser, thicker, and darker terminal hair through sexual differentiation, women do not, leaving their vellus hair visible.

Texture

Curly hair

Yellow curly hair and scalp from body which had long black wig over hair. Parts of wig plait remains. From Egypt, Gurob, probably tomb 23. 18th-19th Dynasty. The Petrie Museum of Egyptian Archaeology, London
Yellow curly hair and scalp from body which had long black wig over hair. Parts of wig plait remains. From Egypt, Gurob, probably tomb 23. 18th–19th Dynasty. The Petrie Museum of Egyptian Archaeology, London
David Luiz ConfedCup2013Champions17
Man with curly hair (David Luiz)

Jablonski[49] asserts head hair was evolutionarily advantageous for pre-humans to retain because it protected the scalp as they walked upright in the intense African (equatorial) UV light. While some might argue that, by this logic, humans should also express hairy shoulders because these body parts would putatively be exposed to similar conditions, the protection of the head, the seat of the brain that enabled humanity to become one of the most successful species on the planet (and which also is very vulnerable at birth) was arguably a more urgent issue (axillary hair in the underarms and groin were also retained as signs of sexual maturity). Sometime during the gradual process by which Homo erectus began a transition from furry skin to the naked skin expressed by Homo sapiens, hair texture putatively gradually changed from straight hair (the condition of most mammals, including humanity's closest cousins—chimpanzees) to Afro-textured hair or 'kinky' (i.e. tightly coiled). This argument assumes that curly hair better impedes the passage of UV light into the body relative to straight hair (thus curly or coiled hair would be particularly advantageous for light-skinned hominids living at the equator).

It is substantiated by Iyengar's (1998) findings that UV light can enter into straight human hair roots (and thus into the body through the skin) via the hair shaft. Specifically, the results of that study suggest that this phenomenon resembles the passage of light through fiber optic tubes (which do not function as effectively when kinked or sharply curved or coiled). In this sense, when hominids (i.e. Homo Erectus) were gradually losing their straight body hair and thereby exposing the initially pale skin underneath their fur to the sun, straight hair would have been an adaptive liability. By inverse logic, later, as humans traveled farther from Africa and/or the equator, straight hair may have (initially) evolved to aid the entry of UV light into the body during the transition from dark, UV-protected skin to paler skin.

Some conversely believe that tightly coiled hair that grows into a typical Afro-like formation would have greatly reduced the ability of the head and brain to cool because although African people's hair is much less dense than its European counterpart's, in the intense sun the effective 'woolly hat' that such hair produced would have been a disadvantage. However, such anthropologists as Nina Jablonski oppositely argue about this hair texture. Specifically, Jablonski's assertions[49] suggest that the adjective "woolly" in reference to Afro-hair is a misnomer in connoting the high heat insulation derivable from the true wool of sheep. Instead, the relatively sparse density of Afro-hair, combined with its springy coils actually results in an airy, almost sponge-like structure that in turn, Jablonski argues,[49] more likely facilitates an increase in the circulation of cool air onto the scalp. Further, wet Afro-hair does not stick to the neck and scalp unless totally drenched and instead tends to retain its basic springy puffiness because it less easily responds to moisture and sweat than straight hair does. In this sense, the trait may enhance comfort levels in intense equatorial climates more than straight hair (which, on the other hand, tends to naturally fall over the ears and neck to a degree that provides slightly enhanced comfort levels in cold climates relative to tightly coiled hair).

Furthermore, some interpret the ideas of Charles Darwin as suggesting that some traits, such as hair texture, were so arbitrary to human survival that the role natural selection played was trivial. Hence, they argue in favor of his suggestion that sexual selection may be responsible for such traits. However, inclinations towards deeming hair texture "adaptively trivial" may root in certain cultural value judgments more than objective logic. In this sense the possibility that hair texture may have played an adaptively significant role cannot be completely eliminated from consideration. In fact, while the sexual selection hypothesis cannot be ruled out, the asymmetrical distribution of this trait vouches for environmental influence. Specifically, if hair texture were simply the result of adaptively arbitrary human aesthetic preferences, one would expect that the global distribution of the various hair textures would be fairly random. Instead, the distribution of Afro-hair is strongly skewed toward the equator.

Further, it is notable that the most pervasive expression of this hair texture can be found in sub-Saharan Africa; a region of the world that abundant genetic and paleo-anthropological evidence suggests, was the relatively recent (≈200,000-year-old) point of origin for modern humanity. In fact, although genetic findings (Tishkoff, 2009) suggest that sub-Saharan Africans are the most genetically diverse continental group on Earth, Afro-textured hair approaches ubiquity in this region. This points to a strong, long-term selective pressure that, in stark contrast to most other regions of the genomes of sub-Saharan groups, left little room for genetic variation at the determining loci. Such a pattern, again, does not seem to support human sexual aesthetics as being the sole or primary cause of this distribution.

Blackhair10
Straight black hair

The EDAR locus

A group of studies have recently shown that genetic patterns at the EDAR locus, a region of the modern human genome that contributes to hair texture variation among most individuals of East Asian descent, support the hypothesis that (East Asian) straight hair likely developed in this branch of the modern human lineage subsequent to the original expression of tightly coiled natural afro-hair.[53][54][55] Specifically, the relevant findings indicate that the EDAR mutation coding for the predominant East Asian 'coarse' or thick, straight hair texture arose within the past ≈65,000 years, which is a time frame that covers from the earliest of the 'Out of Africa' migrations up to now.

Disease

Ringworm is a fungal disease that targets hairy skin.[56]

Premature greying of hair is another condition that results in greying before the age of 20 years in Whites, before 25 years in Asians, and before 30 years in Africans.[57]

Hair care

Hair care involves the hygiene and cosmetology of hair including hair on the scalp, facial hair (beard and moustache), pubic hair and other body hair. Hair care routines differ according to an individual's culture and the physical characteristics of one's hair. Hair may be colored, trimmed, shaved, plucked, or otherwise removed with treatments such as waxing, sugaring, and threading.

Removal practices

Depilation is the removal of hair from the surface of the skin. This can be achieved through methods such as shaving. Epilation is the removal of the entire hair strand, including the part of the hair that has not yet left the follicle. A popular way to epilate hair is through waxing.

Shaving

Shaving-system-2blade
Many razors have multiple blades purportedly to ensure a close shave. While shaving initially will leave skin feeling smooth and hair free, new hair growth can appear a few hours after hair removal.

Shaving is accomplished with bladed instruments, such as razors. The blade is brought close to the skin and stroked over the hair in the desired area to cut the terminal hairs and leave the skin feeling smooth. Depending upon the rate of growth, one can begin to feel the hair growing back within hours of shaving. This is especially evident in men who develop a five o'clock shadow after having shaved their faces. This new growth is called stubble. Stubble typically appears to grow back thicker because the shaved hairs are blunted instead of tapered off at the end, although the hair never actually grows back thicker.

Waxing

Waxing involves using a sticky wax and strip of paper or cloth to pull hair from the root. Waxing is the ideal hair removal technique to keep an area hair-free for long periods of time. It can take three to five weeks for waxed hair to begin to resurface again. Hair in areas that have been waxed consistently is known to grow back finer and thinner, especially compared to hair that has been shaved with a razor.

Laser removal

Laser hair removal is a cosmetic method where a small laser beam pulses selective heat on dark target matter in the area that causes hair growth without harming the skin tissue. This process is repeated several times over the course of many months to a couple of years with hair regrowing less frequently until it finally stops; this is used as a more permanent solution to waxing or shaving. Laser removal is practiced in many clinics along with many at-home products.

Cutting and trimming

Because the hair on one's head is normally longer than other types of body hair, it is cut with scissors or clippers. People with longer hair will most often use scissors to cut their hair, whereas shorter hair is maintained using a trimmer. Depending on the desired length and overall health of the hair, periods without cutting or trimming the hair can vary.

Cut hair may be used in wigs. Global imports of hair in 2010 was worth $US 1.24 billion.[58]

Social role

Alessandro Allori - Portrait of Bianca Cappello
Portrait of a Woman, Alessandro Allori (1535–1607; Uffizi Gallery): a plucked hairline gives a fashionably "noble brow"

Hair has great social significance for human beings.[59] [60] It can grow on most external areas of the human body, except on the palms of the hands and the soles of the feet (among other areas). Hair is most noticeable on most people in a small number of areas, which are also the ones that are most commonly trimmed, plucked, or shaved. These include the face, ears, head, eyebrows, legs, and armpits, as well as the pubic region. The highly visible differences between male and female body and facial hair are a notable secondary sex characteristic.

The world's longest documented hair belongs to Xie Qiuping (China), at 5.627 m (18 ft 5.54 in) when measured on 8 May 2004. She has been growing her hair since 1973, from the age of 13.[61]

Indication of status

Healthy hair indicates health and youth (important in evolutionary biology). Hair color and texture can be a sign of ethnic ancestry. Facial hair is a sign of puberty in men. White hair is a sign of age or genetics, which may be concealed with hair dye (not easily for some), although many prefer to assume it (especially if it is a poliosis characteristic of the person since childhood). Male pattern baldness is a sign of age, which may be concealed with a toupee, hats, or religious and cultural adornments. Although drugs and medical procedures exist for the treatment of baldness, many balding men simply shave their heads. In early modern China, the queue was a male hairstyle worn by the Manchus from central Manchuria and the Han Chinese during the Qing dynasty; hair on the front of the head was shaved off above the temples every ten days, mimicking male-pattern baldness, and the rest of the hair braided into a long pigtail.

Hairstyle may be an indicator of group membership. During the English Civil War, the followers of Oliver Cromwell decided to crop their hair close to their head, as an act of defiance to the curls and ringlets of the king's men.[62] This led to the Parliamentary faction being nicknamed Roundheads. Recent isotopic analysis of hair is helping to shed further light on sociocultural interaction, giving information on food procurement and consumption in the 19th century .[63] Having bobbed hair was popular among the flappers in the 1920s as a sign of rebellion against traditional roles for women. Female art students known as the "cropheads" also adopted the style, notably at the Slade School in London, England. Regional variations in hirsutism cause practices regarding hair on the arms and legs to differ. Some religious groups may follow certain rules regarding hair as part of religious observance. The rules often differ for men and women.

Many subcultures have hairstyles which may indicate an unofficial membership. Many hippies, metalheads and Indian sadhus have long hair, as well many older indie kids. Many punks wear a hairstyle known as a mohawk or other spiked and dyed hairstyles; skinheads have short-cropped or completely shaved heads. Long stylized bangs were very common for emos, scene kids and younger indie kids in the 2000s and early 2010s, among people of both genders.

Heads were shaved in concentration camps, and head-shaving has been used as punishment, especially for women with long hair. The shaven head is common in military haircuts, while Western monks are known for the tonsure. By contrast, among some Indian holy men, the hair is worn extremely long.

In the time of Confucius (5th century BCE), the Chinese grew out their hair and often tied it, as a symbol of filial piety.

Regular hairdressing in some cultures is considered a sign of wealth or status. The dreadlocks of the Rastafari movement were despised early in the movement's history. In some cultures, having one's hair cut can symbolize a liberation from one's past, usually after a trying time in one's life. Cutting the hair also may be a sign of mourning.

Tightly coiled hair in its natural state may be worn in an Afro. This hairstyle was once worn among African Americans as a symbol of racial pride. Given that the coiled texture is the natural state of some African Americans' hair, or perceived as being more "African", this simple style is now often seen as a sign of self-acceptance and an affirmation that the beauty norms of the (eurocentric) dominant culture are not absolute. It is important to note that African Americans as a whole have a variety of hair textures, as they are not an ethnically homogeneous group, but an ad-hoc of different racial admixtures.

The film Easy Rider (1969) includes the assumption that the two main characters could have their long hairs forcibly shaved with a rusty razor when jailed, symbolizing the intolerance of some conservative groups toward members of the counterculture. At the conclusion of the Oz obscenity trials in the UK in 1971, the defendants had their heads shaved by the police, causing public outcry. During the appeal trial, they appeared in the dock wearing wigs.[64] A case where a 14-year-old student was expelled from school in Brazil in the mid-2000s, allegedly because of his fauxhawk haircut, sparked national debate and legal action resulting in compensation.[65][66]

Religious practices

Women's hair may be hidden using headscarves, a common part of the hijab in Islam and a symbol of modesty required for certain religious rituals in Eastern Orthodoxy. Russian Orthodox Church requires all married women to wear headscarves inside the church; this tradition is often extended to all women, regardless of marital status. Orthodox Judaism also commands the use of scarves and other head coverings for married women for modesty reasons. Certain Hindu sects also wear head scarves for religious reasons. Sikhs have an obligation not to cut hair (a Sikh cutting hair becomes 'apostate' which means fallen from religion)[67] and men keep it tied in a bun on the head, which is then covered appropriately using a turban. Multiple religions, both ancient and contemporary, require or advise one to allow their hair to become dreadlocks, though people also wear them for fashion. For men, Islam, Orthodox Judaism, Orthodox Christianity, Roman Catholicism, and other religious groups have at various times recommended or required the covering of the head and sections of the hair of men, and some have dictates relating to the cutting of men's facial and head hair. Some Christian sects throughout history and up to modern times have also religiously proscribed the cutting of women's hair. For some Sunni madhabs, the donning of a kufi or topi is a form of sunnah.[68]

See also

References

Notes

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External links

Alopecia areata

Alopecia areata, also known as spot baldness, is a condition in which hair is lost from some or all areas of the body. Often it results in a few bald spots on the scalp, each about the size of a coin. Psychological stress may result. People are generally otherwise healthy. In a few cases, all the hair on the scalp or all body hair is lost and loss can be permanent.Alopecia areata is believed to be an autoimmune disease resulting from a breach in the immune privilege of the hair follicles. Risk factors include a family history of the condition. Among identical twins if one is affected the other has about a 50% chance of also being affected. The underlying mechanism involves failure by the body to recognize its own cells with subsequent immune mediated destruction of the hair follicle.There is no cure for the condition. Efforts may be used to try to speed hair regrowth such as cortisone injections. Sunscreen, head coverings to protect from cold and sun, and glasses if the eyelashes are missing is recommended. In some cases the hair regrows and the condition does not reoccur. In others hair loss and regrowth occurs over years. Among those in whom all body hair is lost less than 10% recover.About 0.15% of people are affected at any one time and 2% of people are affected at some point in time. Onset is usually in childhood. Males and females have the condition in equal numbers. The condition does not affect a person's life expectancy.

Blond

Blond or fair hair is a hair color characterized by low levels of the dark pigment eumelanin. The resultant visible hue depends on various factors, but always has some yellowish color. The color can be from the very pale blond (caused by a patchy, scarce distribution of pigment) to reddish "strawberry" blond or golden-brownish ("sandy") blond colors (the latter with more eumelanin). Because hair color tends to darken with age, natural blond hair is generally rare in adulthood. Naturally-occurring blond hair is primarily found in populations of northern European descent and is believed to have evolved to enable more efficient synthesis of vitamin D, due to northern Europe's lower levels of sunlight. Blond hair has also developed in other populations, although it is usually not as common, and can be found among natives of the Solomon Islands, Vanuatu, and Fiji, among the Berbers of North Africa, and among some Asians.

In Western culture, blond hair has long been associated with female beauty. Aphrodite, the Greek goddess of love and beauty, was reputed to have blond hair. In ancient Greece and Rome, blond hair was frequently associated with prostitutes, who dyed their hair using saffron dyes in order to attract customers. The Greeks stereotyped Thracians and slaves as blond and the Romans associated blondness with the Celts and the Germans to the north. In western Europe during the Middle Ages, long, blond hair was idealized as the paragon of female beauty. The Norse goddess Sif and the medieval heroine Iseult were both significantly portrayed as blond and, in medieval artwork, Eve, Mary Magdalene, and the Virgin Mary are often shown with blond hair. In the late nineteenth and early twentieth century, scientific racists categorized blond hair and blue eyes as characteristics of the supreme Nordic race. In contemporary western culture, blonde women are often negatively stereotyped as sexually attractive, but unintelligent.

Brown hair

Brown hair is the second most common human hair color, after black hair. It varies from light brown to almost black hair. It is characterized by higher levels of the dark pigment eumelanin and lower levels of the pale pigment pheomelanin. People with brown hair are often referred to as brunette, which in French is the feminine form of brunet, the diminutive of brun (brown, brown-haired or dark-haired).Brown hair is common among populations in the Western world, especially among those from Central Europe, Southeastern Europe, Eastern Europe, Southern Europe, Southern Cone, the United States, and also some populations in the Greater Middle East where it transitions smoothly into black hair. Additionally, brown hair is common among Australian Aborigines and Melanesians.

Dreadlocks

Dreadlocks, also locs, dreads, or in Sanskrit, Jaṭā, are ropelike strands of hair formed by matting or braiding hair. Earliest depictions of dreadlocks date from over 2,000 years ago.

Fur

Fur is a thick growth of hair that covers the skin of many animals. It is a defining characteristic of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture and the underfur acts as an insulating blanket that keeps the animal warm.The fur of mammals has many uses: protection, sensory purposes, waterproofing, and camouflage, with the primary usage being thermoregulation. The types of hair include definitive, which may be shed after reaching a certain length; vibrissae, which are sensory hairs and are most commonly whiskers; pelage, which consists of guard hairs, under-fur, and awn hair; spines, which are a type of stiff guard hair used for defense in, for example, porcupines; bristles, which are long hairs usually used in visual signals, such as the mane of a lion; velli, often called "down fur," which insulates newborn mammals; and wool, which is long, soft, and often curly. Hair length is negligible in thermoregulation, as some tropical mammals, such as sloths, have the same fur length as some arctic mammals but with less insulation; and, conversely, other tropical mammals with short hair have the same insulating value as arctic mammals. The denseness of fur can increase an animal's insulation value, and arctic mammals especially have dense fur; for example, the musk ox has guard hairs measuring 30 cm (12 in) as well as a dense underfur, which forms an airtight coat, allowing them to survive in temperatures of −40 °C (−40 °F). Some desert mammals, such as camels, use dense fur to prevent solar heat from reaching their skin, allowing the animal to stay cool; a camel's fur may reach 70 °C (158 °F) in the summer, but the skin stays at 40 °C (104 °F). Aquatic mammals, conversely, trap air in their fur to conserve heat by keeping the skin dry.

Mammalian coats are colored for a variety of reasons, the major selective pressures including camouflage, sexual selection, communication, and physiological processes such as temperature regulation. Camouflage is a powerful influence in a large number of mammals, as it helps to conceal individuals from predators or prey. Aposematism, warning off possible predators, is the most likely explanation of the black-and-white pelage of many mammals which are able to defend themselves, such as in the foul-smelling skunk and the powerful and aggressive honey badger. In arctic and subarctic mammals such as the arctic fox (Alopex lagopus), collared lemming (Dicrostonyx groenlandicus), stoat (Mustela erminea), and snowshoe hare (Lepus americanus), seasonal color change between brown in summer and white in winter is driven largely by camouflage. Differences in female and male coat color may indicate nutrition and hormone levels, important in mate selection. Some arboreal mammals, notably primates and marsupials, have shades of violet, green, or blue skin on parts of their bodies, indicating some distinct advantage in their largely arboreal habitat due to convergent evolution. The green coloration of sloths, however, is the result of a symbiotic relationship with algae. Coat color is sometimes sexually dimorphic, as in many primate species. Coat color may influence the ability to retain heat, depending on how much light is reflected. Mammals with a darker colored coat can absorb more heat from solar radiation, and stay warmer, and some smaller mammals, such as voles, have darker fur in the winter. The white, pigmentless fur of arctic mammals, such as the polar bear, may reflect more solar radiation directly onto the skin.The term pelage – first known use in English c. 1828 (French, from Middle French, from poil for "hair", from Old French peilss, from Latin pilus) – is sometimes used to refer to an animal's complete coat. The term fur is also used to refer to animal pelts which have been processed into leather with their hair still attached. The words fur or furry are also used, more casually, to refer to hair-like growths or formations, particularly when the subject being referred to exhibits a dense coat of fine, soft "hairs". If layered, rather than grown as a single coat, it may consist of short down hairs, long guard hairs, and in some cases, medium awn hairs. Mammals with reduced amounts of fur are often called "naked", as with the naked mole-rat, or "hairless", as with hairless dogs.

An animal with commercially valuable fur is known within the fur industry as a furbearer. The use of fur as clothing or decoration is controversial; animal welfare advocates object to the trapping and killing of wildlife, and to the confinement and killing of animals on fur farms.

Glam metal

Glam metal (also known pejoratively as hair metal and often used synonymously with pop metal) is a subgenre of heavy metal, which features pop-influenced hooks and guitar riffs, and borrows from the fashion of 1970s glam rock.

Glam metal is influenced by music acts like Alice Cooper, Cheap Trick, Kiss, and Van Halen. It arose in the late 1970s and early 1980s in the United States, particularly on the Los Angeles Sunset Strip music scene, pioneered by bands such as Mötley Crüe, Ratt, Quiet Riot, Twisted Sister, Stryper, Def Leppard, Bon Jovi, and Dokken. It was also popular throughout the mid-late 1980s and early 1990s bringing to prominence bands including Poison, Skid Row, Cinderella and Warrant. Glam metal is associated with flashy clothing, makeup and notable for an overall androgynous aesthetic. Poison, for example, have long shaggy or backcombed hair, accessories, metal studs, leather, and make-up during their live performances.

Glam metal lost mainstream interest in the early 1990s as the perceived excesses of glam metal created a backlash against the genre. A factor in the decline of glam metal was the rise of grunge in the early 1990s, which had a stripped-down aesthetic and a complete rejection of the glam metal visual style. Glam metal has returned since the late 1990s and mid 2000s with reunions of many popular acts from the genre, as well as newer bands from the 2000s/2010s including the Darkness, Santa Cruz, Reckless Love and Steel Panther.

Glam rock

Glam rock is a style of rock music that developed in the United Kingdom in the early 1970s performed by musicians who wore outrageous costumes, makeup, and hairstyles, particularly platform shoes and glitter. Glam artists drew on diverse sources across music and throwaway pop culture, ranging from bubblegum pop and 1950s rock and roll to cabaret, science fiction, and complex art rock. The flamboyant clothing and visual styles of performers were often camp or androgynous, and have been described as playing with nontraditional gender roles. "Glitter rock" was another term used to refer to a more extreme version of glam.The UK charts were inundated with glam rock acts from 1971 to 1975. The March 1971 appearance of T. Rex frontman Marc Bolan on the BBC's music show Top of the Pops, wearing glitter and satins, is often cited as the beginning of the movement. Other British glam rock artists include David Bowie, Mott the Hoople, Sweet, Slade, Mud, Roxy Music and Gary Glitter. Those not central to the genre, such as Elton John, Rod Stewart and Freddie Mercury of Queen, also adopted glam styles. In the US the scene was much less prevalent, with Alice Cooper and Lou Reed the only American artists to score a hit. Other US glam artists include New York Dolls, Iggy Pop and Jobriath. It declined after the mid-1970s, but influenced other musical genres including punk rock, glam metal, New Romantic, deathrock and gothic rock. Glam rock has sporadically revived since the 1990s.

Hair (musical)

Hair: The American Tribal Love-Rock Musical is a rock musical with a book and lyrics by Gerome Ragni and James Rado and music by Galt MacDermot. A product of the hippie counterculture and sexual revolution of the late 1960s, several of its songs became anthems of the anti-Vietnam War peace movement. The musical's profanity, its depiction of the use of illegal drugs, its treatment of sexuality, its irreverence for the American flag, and its nude scene caused much comment and controversy. The musical broke new ground in musical theatre by defining the genre of "rock musical", using a racially integrated cast, and inviting the audience onstage for a "Be-In" finale.Hair tells the story of the "tribe", a group of politically active, long-haired hippies of the "Age of Aquarius" living a bohemian life in New York City and fighting against conscription into the Vietnam War. Claude, his good friend Berger, their roommate Sheila and their friends struggle to balance their young lives, loves, and the sexual revolution with their rebellion against the war and their conservative parents and society. Ultimately, Claude must decide whether to resist the draft as his friends have done, or to succumb to the pressures of his parents (and conservative America) to serve in Vietnam, compromising his pacifist principles and risking his life.

After an off-Broadway debut on October 17, 1967, at Joseph Papp's Public Theater and a subsequent run at the Cheetah nightclub from December 1967 through January 1968, the show opened on Broadway in April 1968 and ran for 1,750 performances. Simultaneous productions in cities across the United States and Europe followed shortly thereafter, including a successful London production that ran for 1,997 performances. Since then, numerous productions have been staged around the world, spawning dozens of recordings of the musical, including the 3 million-selling original Broadway cast recording. Some of the songs from its score became Top 10 hits, and a feature film adaptation was released in 1979. A Broadway revival opened in 2009, earning strong reviews and winning the Tony Award and Drama Desk Award for Best Revival of a Musical. In 2008, Time wrote, "Today Hair seems, if anything, more daring than ever."

Hair coloring

Hair coloring, or hair dyeing, is the practice of changing the hair color. The main reasons for this are cosmetic: to cover gray or white hair, to change to a color regarded as more fashionable or desirable, or to restore the original hair color after it has been discolored by hairdressing processes or sun bleaching.

Hair coloring can be done professionally by a hairdresser or independently at home. Today, hair coloring is very popular, with 75% of women and 18% of men living in Copenhagen having reported using hair dye according to a study by the University of Copenhagen. At-home coloring in the United States reached $1.9 billion in 2011 and is expected to rise to $2.2 billion by 2016.

Hair follicle

The hair follicle is a dynamic organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between hormones, neuropeptides and immune cells. This complex interaction induces the hair follicle to produce different types of hair as seen on different parts of the body. For example, terminal hairs grow on the scalp and lanugo hairs are seen covering the bodies of fetuses in the uterus and in some new born babies. The process of hair growth occurs in distinct sequential stages. The first stage is called anagen and is the active growth phase, telogen is the resting stage, catagen is the regression of the hair follicle phase, exogen is the active shedding of hair phase and lastly kenogen is the phase between the empty hair follicle and the growth of new hair.The function of hair in humans has long been a subject of interest and continues to be an important topic in society, developmental biology and medicine. Of all mammals, humans have the longest growth phase of scalp hair compared to hair growth on other parts of the body. For centuries, humans have ascribed esthetics to scalp hair styling and dressing and it is often used to communicate social or cultural norms in societies. In addition to its role in defining human appearance, scalp hair also provides protection from UV sun rays and is an insulator against extremes of hot and cold temperatures. Differences in the shape of the scalp hair follicle determine the observed ethnic differences in scalp hair appearance, length and texture.

There are many human diseases in which abnormalities in hair appearance, texture or growth are early signs of local disease of the hair follicle or systemic illness. Well known diseases of the hair follicle include alopecia or hair loss, hirsutism or excess hair growth and lupus erythematosus.

Hair loss

Hair loss, also known as alopecia or baldness, refers to a loss of hair from part of the head or body. Typically at least the head is involved. The severity of hair loss can vary from a small area to the entire body. Typically inflammation or scarring is not present. Hair loss in some people causes psychological distress.Common types include: male-pattern hair loss, female-pattern hair loss, alopecia areata, and a thinning of hair known as telogen effluvium. The cause of male-pattern hair loss is a combination of genetics and male hormones, the cause of female pattern hair loss is unclear, the cause of alopecia areata is autoimmune, and the cause of telogen effluvium is typically a physically or psychologically stressful event. Telogen effluvium is very common following pregnancy.Less common causes of hair loss without inflammation or scarring include the pulling out of hair, certain medications including chemotherapy, HIV/AIDS, hypothyroidism, and malnutrition including iron deficiency. Causes of hair loss that occurs with scarring or inflammation include fungal infection, lupus erythematosus, radiation therapy, and sarcoidosis. Diagnosis of hair loss is partly based on the areas affected.Treatment of pattern hair loss may simply involve accepting the condition. Interventions that can be tried include the medications minoxidil (or finasteride) and hair transplant surgery. Alopecia areata may be treated by steroid injections in the affected area, but these need to be frequently repeated to be effective. Hair loss is a common problem. Pattern hair loss by age 50 affects about half of males and a quarter of females. About 2% of people develop alopecia areata at some point in time.

Hairstyle

A hairstyle, hairdo, or haircut refers to the styling of hair, usually on the human scalp. Sometimes, this could also mean an editing of facial or body hair. The fashioning of hair can be considered an aspect of personal grooming, fashion, and cosmetics, although practical, cultural, and popular considerations also influence some hairstyles.The oldest known depiction of hair styling is hair braiding which dates back about 30,000 years. In history, women's hair was often elaborately and carefully dressed in special ways. From the time of the Roman Empire until the Middle Ages, most women grew their hair as long as it would naturally grow. Between the late 15th century and the 16th century, a very high hairline on the forehead was considered attractive. Around the same time period, European men often wore their hair cropped no longer than shoulder-length. In the early 17th century, male hairstyles grew longer, with waves or curls being considered desirable.

The male wig was pioneered by King Louis XIII of France (1601–1643) in 1624. Perukes or periwigs for men were introduced into the English-speaking world with other French styles in 1660. Late 17th-century wigs were very long and wavy, but became shorter in the mid-18th century, by which time they were normally white. Short hair for fashionable men was a product of the Neoclassical movement. In the early 19th century the male beard, and also moustaches and sideburns, made a strong reappearance. From the 16th to the 19th century, European women's hair became more visible while their hair coverings grew smaller. In the middle of the 18th century the pouf style developed. During the First World War, women around the world started to shift to shorter hairstyles that were easier to manage. In the early 1950s women's hair was generally curled and worn in a variety of styles and lengths. In the 1960s, many women began to wear their hair in short modern cuts such as the pixie cut, while in the 1970s, hair tended to be longer and looser. In both the 1960s and 1970s many men and women wore their hair very long and straight. In the 1980s, women pulled back their hair with scrunchies. During the 1980s, punk hairstyles were adopted by many people.

Human hair color

Hair color is the pigmentation of hair follicles due to two types of melanin: eumelanin and pheomelanin. Generally, if more eumelanin is present, the color of the hair is darker; if less eumelanin is present, the hair is lighter. Levels of melanin can vary over time causing a person's hair color to change, and it is possible to have hair follicles of more than one color on the same person. Particular hair colors are often associated with ethnic groups, while gray or white hair is associated with age.

Minoxidil

Minoxidil is a medication used for the treatment of male-pattern hair loss. It is an antihypertensive vasodilator. It is available as a generic medication and over the counter.

Pattern hair loss

Pattern hair loss, known as male-pattern hair loss (MPHL) when it affects males and female-pattern hair loss (FPHL) when it affects females, is hair loss that primarily affects the top and front of the scalp. In males, the hair loss often presents itself as a receding hairline, while in females, it typically presents as a thinning of the hair.Male pattern hair loss is believed to be due to a combination of genetics and the male hormone dihydrotestosterone. The cause in female pattern hair loss remains unclear.Management may include simply accepting the condition. Otherwise, treatments may include minoxidil, finasteride, or hair transplant surgery. Evidence for finasteride in women is poor and it may result in birth defects if taken during pregnancy.Pattern hair loss by the age of 50 affects about half of males and a quarter of females. It is the most common cause of hair loss.

Professional wrestling match types

Many types of wrestling matches, sometimes called "concept" or "gimmick matches" in the jargon of the business, are performed in professional wrestling. Some of them occur relatively frequently while others are developed so as to advance an angle and such match types are used rarely. Because of professional wrestling's long history over decades, many things have been recycled (many match types often being variations of previous match types). These match types can be organized into several loose groups.

Pubic hair

Pubic hair is terminal body hair that is found in the genital area of adolescent and adult humans. The hair is located on and around the sex organs and sometimes at the top of the inside of the thighs. In the pubic region around the pubis bone, it is known as a pubic patch. Pubic hair is found on the scrotum in the male and on the vulva in the female.

Although fine vellus hair is present in the area in childhood, pubic hair is considered to be the heavier, longer and coarser hair that develops during puberty as an effect of rising levels of androgens in males and estrogens in females. Pubic hair differs from other hair on the body and is a secondary sex characteristic. Many cultures regard pubic hair as erotic, and in most cultures pubic hair is associated with the genitals, which both men and women are expected to keep covered at all times. In some cultures, it is the norm for pubic hair to be removed, especially of females; the practice is regarded as part of personal hygiene. In other cultures, the exposure of pubic hair (for example, when wearing a swimsuit) may be regarded as unaesthetic or embarrassing and is therefore trimmed or otherwise styled to avoid it being visible. Pubic hair fetishism, or pubephilia, is where a person becomes sexually aroused by the sight or feel of human pubic hair.

Red hair

Red hair (or ginger hair) occurs naturally in one to two percent of the human population, appearing with greater frequency (two to six percent) among people of Northern or Northwestern European ancestry and lesser frequency in other populations. It is most common in individuals homozygous for a recessive allele on chromosome 16 that produces an altered version of the MC1R protein.Red hair varies in hue from a deep burgundy or bright copper (auburn) to burnt orange or red-orange to and strawberry blond. Characterized by high levels of the reddish pigment pheomelanin and relatively low levels of the dark pigment eumelanin, it is associated with fair skin color, lighter eye color, freckles, and sensitivity to ultraviolet light.Cultural reactions to red hair have varied from ridicule to admiration with many common stereotypes in existence regarding redheads. The term redhead has been in use since at least 1510.

Trichotillomania

Trichotillomania (TTM), also known as hair pulling disorder, is a mental disorder characterised by a long term urge that results in the pulling out of one's hair. This occurs to such a degree that hair loss can be seen. Efforts to stop pulling hair typically fail. Hair removal may occur anywhere; however, the head and around the eyes are most common. The hair pulling is to such a degree that it results in distress.The disorder may run in families. It occurs more commonly in those with obsessive compulsive disorder. Episodes of pulling may be triggered by anxiety. People usually acknowledge that they pull their hair. On examination broken hairs may be seen. Other conditions that may present similarly include body dysmorphic disorder, however in that condition people remove hair to try to improve what they see as a problem in how they look.Treatment is typically with cognitive behavioral therapy. The medication clomipramine may also be helpful. Trichotillomania is estimated to affect one to four percent of people. Trichotillomania most commonly begins in childhood or adolescence. Women are more commonly affected than men. The name was created by François Henri Hallopeau in 1889, from the Greek θρίξ/τριχ; thrix (meaning "hair"), along with τίλλειν; tíllein (meaning "to pull"), and μανία; mania (meaning "madness").

Human hair
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Facial hair
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Haircare products
Haircare techniques
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