Hair

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For other uses, see Hair (disambiguation). Hair_sentence_0

"Hairy" redirects here. Hair_sentence_1

For the epithet, see List of people known as the Hairy. Hair_sentence_2

For the gene, see Hairy (gene). Hair_sentence_3

"Glabrousness" redirects here. Hair_sentence_4

For other uses, see Glabrousness (disambiguation). Hair_sentence_5

Not to be confused with Fur. Hair_sentence_6

Hair_table_infobox_0

HairHair_header_cell_0_0_0
DetailsHair_header_cell_0_1_0
SystemHair_header_cell_0_2_0 Integumentary systemHair_cell_0_2_1
IdentifiersHair_header_cell_0_3_0
LatinHair_header_cell_0_4_0 capillumHair_cell_0_4_1
MeSHHair_header_cell_0_5_0 Hair_cell_0_5_1
TA98Hair_header_cell_0_6_0 Hair_cell_0_6_1
TA2Hair_header_cell_0_7_0 Hair_cell_0_7_1
THHair_header_cell_0_8_0 Hair_cell_0_8_1
FMAHair_header_cell_0_9_0 Hair_cell_0_9_1

Hair is a protein filament that grows from follicles found in the dermis. Hair_sentence_7

Hair is one of the defining characteristics of mammals. Hair_sentence_8

The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fine vellus hair. Hair_sentence_9

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. Hair_sentence_10

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. Hair_sentence_11

Overview Hair_section_0

The word "hair" usually refers to two distinct structures: Hair_sentence_12

Hair_ordered_list_0

  1. 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.Hair_item_0_0
  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_item_0_1

Hair fibers have a structure consisting of several layers, starting from the outside: Hair_sentence_13

Hair_ordered_list_1

  1. the cuticle, which consists of several layers of flat, thin cells laid out overlapping one another as roof shinglesHair_item_1_2
  2. the cortex, which contains the keratin bundles in cell structures that remain roughly rod-likeHair_item_1_3
  3. the medulla, a disorganized and open area at the fiber's centerHair_item_1_4

Description Hair_section_1

Each strand of hair is made up of the medulla, cortex, and cuticle. Hair_sentence_14

The innermost region, the medulla, is not always present and is an open, unstructured region. Hair_sentence_15

The highly structural and organized cortex, or second of three layers of the hair, is the primary source of mechanical strength and water uptake. Hair_sentence_16

The cortex contains melanin, which colors the fiber based on the number, distribution and types of melanin granules. Hair_sentence_17

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. Hair_sentence_18

People with straight hair have round hair fibers. Hair_sentence_19

Oval and other shaped fibers are generally more wavy or curly. Hair_sentence_20

The cuticle is the outer covering. Hair_sentence_21

Its complex structure slides as the hair swells and is covered with a single molecular layer of lipid that makes the hair repel water. Hair_sentence_22

The diameter of human hair varies from 0.017 to 0.18 millimeters (0.00067 to 0.00709 in). Hair_sentence_23

There are two million small, tubular glands and sweat glands that produce watery fluids that cool the body by evaporation. Hair_sentence_24

The glands at the opening of the hair produce a fatty secretion that lubricates the hair. Hair_sentence_25

Hair growth begins inside the hair follicle. Hair_sentence_26

The only "living" portion of the hair is found in the follicle. Hair_sentence_27

The hair that is visible is the hair shaft, which exhibits no biochemical activity and is considered "dead". Hair_sentence_28

The base of a hair's root (the "bulb") contains the cells that produce the hair shaft. Hair_sentence_29

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. Hair_sentence_30

In humans with little body hair, the effect results in goose bumps. Hair_sentence_31

Root of the hair Hair_section_2

Hair_table_infobox_1

Root of the hairHair_header_cell_1_0_0
DetailsHair_header_cell_1_1_0
IdentifiersHair_header_cell_1_2_0
LatinHair_header_cell_1_3_0 radix piliHair_cell_1_3_1
MeSHHair_header_cell_1_4_0 Hair_cell_1_4_1
TA98Hair_header_cell_1_5_0 Hair_cell_1_5_1
TA2Hair_header_cell_1_6_0 Hair_cell_1_6_1
THHair_header_cell_1_7_0 Hair_cell_1_7_1
FMAHair_header_cell_1_8_0 Hair_cell_1_8_1

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. Hair_sentence_32

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. Hair_sentence_33

Natural color Hair_section_3

Main article: Human hair color Hair_sentence_34

All natural hair colors are the result of two types of hair pigments. Hair_sentence_35

Both of these pigments are melanin types, produced inside the hair follicle and packed into granules found in the fibers. Hair_sentence_36

Eumelanin is the dominant pigment in brown hair and black hair, while pheomelanin is dominant in red hair. Hair_sentence_37

Blond hair is the result of having little pigmentation in the hair strand. Hair_sentence_38

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. Hair_sentence_39

Human hair growth Hair_section_4

Main article: Human hair growth Hair_sentence_40

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_sentence_41

Hair follows a specific growth cycle with three distinct and concurrent phases: anagen, catagen, and telogen phases; all three occur simultaneously throughout the body. Hair_sentence_42

Each has specific characteristics that determine the length of the hair. Hair_sentence_43

The body has different types of hair, including vellus hair and androgenic hair, each with its own type of cellular construction. Hair_sentence_44

The different construction gives the hair unique characteristics, serving specific purposes, mainly, warmth and protection. Hair_sentence_45

Texture Hair_section_5

Hair exists in a variety of textures. Hair_sentence_46

Three main aspects of hair texture are the curl pattern, volume, and consistency. Hair_sentence_47

The derivations of hair texture are not fully understood. Hair_sentence_48

All mammalian hair is composed of keratin, so the make-up of hair follicles is not the source of varying hair patterns. Hair_sentence_49

There are a range of theories pertaining to the curl patterns of hair. Hair_sentence_50

Scientists have come to believe that the shape of the hair shaft has an effect on the curliness of the individual's hair. Hair_sentence_51

A very round shaft allows for fewer disulfide bonds to be present in the hair strand. Hair_sentence_52

This means the bonds present are directly in line with one another, resulting in straight hair. Hair_sentence_53

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. Hair_sentence_54

As the hair follicle shape determines curl pattern, the hair follicle size determines thickness. Hair_sentence_55

While the circumference of the hair follicle expands, so does the thickness of the hair follicle. Hair_sentence_56

An individual's hair volume, as a result, can be thin, normal, or thick. Hair_sentence_57

The consistency of hair can almost always be grouped into three categories: fine, medium, and coarse. Hair_sentence_58

This trait is determined by the hair follicle volume and the condition of the strand. Hair_sentence_59

Fine hair has the smallest circumference, coarse hair has the largest circumference, and medium hair is anywhere between the other two. Hair_sentence_60

Coarse hair has a more open cuticle than thin or medium hair causing it to be the most porous. Hair_sentence_61

Classification systems Hair_section_6

There are various systems that people use to classify their curl patterns. Hair_sentence_62

Being knowledgeable of an individual's hair type is a good start to knowing how to take care of one's hair. Hair_sentence_63

There is not just one method to discovering one's hair type. Hair_sentence_64

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. Hair_sentence_65

Hair_description_list_2

The Andre Walker Hair Typing System is the most widely used system to classify hair. Hair_sentence_66

The system was created by the hairstylist of Oprah Winfrey, Andre Walker. Hair_sentence_67

According to this system there are four types of hair: straight, wavy, curly, kinky. Hair_sentence_68

Hair_unordered_list_3

  • 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.Hair_item_3_5
  • 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.Hair_item_3_6
  • 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.Hair_item_3_7
  • 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.Hair_item_3_8

Hair_table_general_2

Andre Walker hair typesHair_table_caption_2
Type 1: StraightHair_header_cell_2_0_0
1aHair_header_cell_2_1_0 Straight (Fine/Thin)Hair_cell_2_1_1 Hair tends to be very soft, thin, shiny, oily, poor at holding curls, difficult to damage.Hair_cell_2_1_2
1bHair_header_cell_2_2_0 Straight (Medium)Hair_cell_2_2_1 Hair characterized by volume and body.Hair_cell_2_2_2
1cHair_header_cell_2_3_0 Straight (Coarse)Hair_cell_2_3_1 Hair tends to be bone-straight, coarse, difficult to curl.Hair_cell_2_3_2
Type 2: WavyHair_header_cell_2_4_0
2aHair_header_cell_2_5_0 Wavy (Fine/Thin)Hair_cell_2_5_1 Hair has definite "S" pattern, can easily be straightened or curled, usually receptive to a variety of styles.Hair_cell_2_5_2
2bHair_header_cell_2_6_0 Wavy (Medium)Hair_cell_2_6_1 Can tend to be frizzy and a little resistant to styling.Hair_cell_2_6_2
2cHair_header_cell_2_7_0 Wavy (Coarse)Hair_cell_2_7_1 Fairly coarse, frizzy or very frizzy with thicker waves, often more resistant to styling.Hair_cell_2_7_2
Type 3: CurlyHair_header_cell_2_8_0
3aHair_header_cell_2_9_0 Curly (Loose)Hair_cell_2_9_1 Presents a definite "S" pattern, tends to combine thickness, volume, and/or frizziness.Hair_cell_2_9_2
3bHair_header_cell_2_10_0 Curly (Tight)Hair_cell_2_10_1 Presents a definite "S" pattern, curls ranging from spirals to spiral-shaped corkscrewHair_cell_2_10_2
Type 4: KinkyHair_header_cell_2_11_0
4aHair_header_cell_2_12_0 Kinky (Soft)Hair_cell_2_12_1 Hair tends to be very wiry and fragile, tightly coiled and can feature curly patterning.Hair_cell_2_12_2
4bHair_header_cell_2_13_0 Kinky (Wiry)Hair_cell_2_13_1 As 4a but with less defined pattern of curls, looks more like a "Z" with sharp anglesHair_cell_2_13_2

Hair_description_list_4

This is a method which classifies the hair by curl pattern, hair-strand thickness and overall hair volume. Hair_sentence_69

Hair_table_general_3

FIA hair classificationHair_table_caption_3
CurlinessHair_header_cell_3_0_0
StraightHair_cell_3_1_0
1aHair_header_cell_3_2_0 Stick-straight.Hair_cell_3_2_1
1bHair_header_cell_3_3_0 Straight but with a slight body wave adding some volume.Hair_cell_3_3_1
1cHair_header_cell_3_4_0 Straight with body wave and one or two visible S-waves (e.g. at nape of neck or temples).Hair_cell_3_4_1
WavyHair_cell_3_5_0
2aHair_header_cell_3_6_0 Loose with stretched S-waves throughout.Hair_cell_3_6_1
2bHair_header_cell_3_7_0 Shorter with more distinct S-waves (resembling e.g. braided damp hair).Hair_cell_3_7_1
2cHair_header_cell_3_8_0 Distinct S-waves, some spiral curling.Hair_cell_3_8_1
CurlyHair_cell_3_9_0
3aHair_header_cell_3_10_0 Big, loose spiral curls.Hair_cell_3_10_1
3bHair_header_cell_3_11_0 Bouncy ringlets.Hair_cell_3_11_1
3cHair_header_cell_3_12_0 Tight corkscrews.Hair_cell_3_12_1
Very ("Really") curlyHair_cell_3_13_0
4aHair_header_cell_3_14_0 Tightly coiled S-curls.Hair_cell_3_14_1
4bHair_header_cell_3_15_0 Z-patterned (tightly coiled, sharply angled)Hair_cell_3_15_1
4cHair_header_cell_3_16_0 Mostly Z-patterned (tightly kinked, less definition)Hair_cell_3_16_1
StrandsHair_header_cell_3_17_0
FHair_header_cell_3_18_0 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.Hair_cell_3_18_1

MHair_header_cell_3_19_0 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.Hair_cell_3_19_1

CHair_header_cell_3_20_0 Coarse

Thick strands whose shed strands usually are easily identified. Coarse hair feels hard and wiry.Hair_cell_3_20_1

Volume

by circumference of full-hair ponytailHair_header_cell_3_21_0

iHair_header_cell_3_22_0 ThinHair_cell_3_22_1 circumference less than 2 inches (5 centimetres)Hair_cell_3_22_2
iiHair_header_cell_3_23_0 NormalHair_cell_3_23_1 ... from 2 to 4 inches (5 to 10 centimetres)Hair_cell_3_23_2
iiiHair_header_cell_3_24_0 ThickHair_cell_3_24_1 ... more than 4 inches (10 centimetres)Hair_cell_3_24_2

Functions Hair_section_7

Many mammals have fur and other hairs that serve different functions. Hair_sentence_70

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_sentence_71

Hair also has a sensory function, extending the sense of touch beyond the surface of the skin. Hair_sentence_72

Guard hairs give warnings that may trigger a recoiling reaction. Hair_sentence_73

Warmth Hair_section_8

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. Hair_sentence_74

The function of hair in other locations is debated. Hair_sentence_75

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. Hair_sentence_76

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. Hair_sentence_77

These hairs then form a heat-trapping layer above the epidermis. Hair_sentence_78

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. Hair_sentence_79

This is more effective in other mammals whose fur fluffs up to create air pockets between hairs that insulate the body from the cold. Hair_sentence_80

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. Hair_sentence_81

Protection Hair_section_9

In some mammals, such as hedgehogs and porcupines, the hairs have been modified into hard spines or quills. Hair_sentence_82

These are covered with thick plates of keratin and serve as protection against predators. Hair_sentence_83

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. Hair_sentence_84

Touch sense Hair_section_10

Displacement and vibration of hair shafts are detected by hair follicle nerve receptors and nerve receptors within the skin. Hair_sentence_85

Hairs can sense movements of air as well as touch by physical objects and they provide sensory awareness of the presence of ectoparasites. Hair_sentence_86

Some hairs, such as eyelashes, are especially sensitive to the presence of potentially harmful matter. Hair_sentence_87

Eyebrows and eyelashes Hair_section_11

The eyebrows provide moderate protection to the eyes from dirt, sweat and rain. Hair_sentence_88

They also play a key role in non-verbal communication by displaying emotions such as sadness, anger, surprise and excitement. Hair_sentence_89

In many other mammals, they contain much longer, whisker-like hairs that act as tactile sensors. Hair_sentence_90

The eyelash grows at the edges of the eyelid and protects the eye from dirt. Hair_sentence_91

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. Hair_sentence_92

The eye reflexively closes as a result of this sensation. Hair_sentence_93

Evolution Hair_section_12

Hair has its origins in the common ancestor of mammals, the synapsids, about 300 million years ago. Hair_sentence_94

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. Hair_sentence_95

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. Hair_sentence_96

An exceptionally well-preserved skull of Estemmenosuchus, a therapsid from the Upper Permian, shows smooth, hairless skin with what appears to be glandular depressions, though as a semi-aquatic species it might not have been particularly useful to determine the integument of terrestrial species. Hair_sentence_97

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. Hair_sentence_98

More recently, studies on terminal Permian Russian coprolites may suggest that non-mammalian synapsids from that era had fur. Hair_sentence_99

If this is the case, these are the oldest hair remnants known, showcasing that fur occurred as far back as the latest Paleozoic. Hair_sentence_100

Some modern mammals have a special gland in front of each orbit used to preen the fur, called the harderian gland. Hair_sentence_101

Imprints of this structure are found in the skull of the small early mammals like Morganucodon, but not in their cynodont ancestors like Thrinaxodon. Hair_sentence_102

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. Hair_sentence_103

Fur could have evolved from sensory hair (whiskers). Hair_sentence_104

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. Hair_sentence_105

The more advanced therapsids could have had a combination of naked skin, whiskers, and scutes. Hair_sentence_106

A full pelage likely did not evolve until the therapsid-mammal transition. Hair_sentence_107

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. Hair_sentence_108

The high interspecific variability of the size, color, and microstructure of hair often enables the identification of species based on single hair filaments. Hair_sentence_109

In varying degrees most mammals have some skin areas without natural hair. Hair_sentence_110

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, as are the labia minora and glans penis. Hair_sentence_111

There are four main types of mechanoreceptors in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini corpuscles. Hair_sentence_112

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. Hair_sentence_113

Glabrousness is a trait that may be associated with neoteny. Hair_sentence_114

Human hairlessness Hair_section_13

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. Hair_sentence_115

On an individual basis, mutations in the gene HR can lead to complete hair loss, though this is not typical in humans. Hair_sentence_116

Humans may also lose their hair as a result of hormonal imbalance due to drugs or pregnancy. Hair_sentence_117

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. Hair_sentence_118

Additionally, it can be used as a communication tool and as a camouflage. Hair_sentence_119

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. Hair_sentence_120

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. Hair_sentence_121

This list includes elephants, rhinoceroses, hippopotamuses, walruses, some species of pigs, whales and other cetaceans, and naked mole rats. Hair_sentence_122

Most mammals have light skin that is covered by fur, and biologists believe that early human ancestors started out this way also. Hair_sentence_123

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. Hair_sentence_124

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. Hair_sentence_125

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. Hair_sentence_126

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. Hair_sentence_127

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. Hair_sentence_128

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. Hair_sentence_129

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. Hair_sentence_130

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. Hair_sentence_131

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. Hair_sentence_132

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 terminal and vellus hair), as well as a much larger role of testosterone in men. Hair_sentence_133

Sexual selection is the only theory thus far that explains the sexual dimorphism seen in the hair patterns of men and women. Hair_sentence_134

On average, men have more body hair than women. Hair_sentence_135

Males have more terminal hair, especially on the face, chest, abdomen, and back, and females have more vellus hair, which is less visible. Hair_sentence_136

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. Hair_sentence_137

This theory, however, has significant holdings in today's cultural norms. Hair_sentence_138

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. Hair_sentence_139

A further hypothesis is that human hair was reduced in response to ectoparasites. Hair_sentence_140

The "ectoparasite" explanation of modern human nakedness is based on the principle that a hairless primate would harbor fewer parasites. Hair_sentence_141

When our ancestors adopted group-dwelling social arrangements roughly 1.8 mya, ectoparasite loads increased dramatically. Hair_sentence_142

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. Hair_sentence_143

While primate species have communal sleeping arrangements, these groups are always on the move and thus are less likely to harbor ectoparasites. Hair_sentence_144

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. Hair_sentence_145

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. Hair_sentence_146

Giles also connects romantic love to hairlessness. Hair_sentence_147

Another hypothesis is that humans' use of fire caused or initiated the reduction in human hair. Hair_sentence_148

Evolutionary variation Hair_section_14

Evolutionary biologists suggest that the genus Homo arose in East Africa approximately 2.5 million years ago. Hair_sentence_149

They devised new hunting techniques. Hair_sentence_150

The higher protein diet led to the evolution of larger body and brain sizes. Hair_sentence_151

Jablonski 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. Hair_sentence_152

As a result, humans evolved the ability to sweat: a process which was facilitated by the loss of body hair. Hair_sentence_153

Another factor in human evolution that also occurred in the prehistoric past was a preferential selection for neoteny, particularly in females. Hair_sentence_154

The idea that adult humans exhibit certain neotenous (juvenile) features, not evinced in the great apes, is about a century old. Hair_sentence_155

Louis Bolk made a long list of such traits, and Stephen Jay Gould published a short list in Ontogeny and Phylogeny. Hair_sentence_156

In addition, paedomorphic characteristics in women are often acknowledged as desirable by men in developed countries. Hair_sentence_157

For instance, vellus hair is a juvenile characteristic. Hair_sentence_158

However, while men develop longer, coarser, thicker, and darker terminal hair through sexual differentiation, women do not, leaving their vellus hair visible. Hair_sentence_159

Further information: Human evolutionary genetics Hair_sentence_160

Texture Hair_section_15

Curly hair Hair_section_16

The EDAR locus Hair_section_17

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. Hair_sentence_161

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. Hair_sentence_162

Disease Hair_section_18

See also: Hair diseases Hair_sentence_163

Ringworm is a fungal disease that targets hairy skin. Hair_sentence_164

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. Hair_sentence_165

Hair care Hair_section_19

Main article: Hair care Hair_sentence_166

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_sentence_167

Hair care routines differ according to an individual's culture and the physical characteristics of one's hair. Hair_sentence_168

Hair may be colored, trimmed, shaved, plucked, or otherwise removed with treatments such as waxing, sugaring, and threading. Hair_sentence_169

Removal practices Hair_section_20

Depilation is the removal of hair from the surface of the skin. Hair_sentence_170

This can be achieved through methods such as shaving. Hair_sentence_171

Epilation is the removal of the entire hair strand, including the part of the hair that has not yet left the follicle. Hair_sentence_172

A popular way to epilate hair is through waxing. Hair_sentence_173

Shaving Hair_section_21

Shaving is accomplished with bladed instruments, such as razors. Hair_sentence_174

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. Hair_sentence_175

Depending upon the rate of growth, one can begin to feel the hair growing back within hours of shaving. Hair_sentence_176

This is especially evident in men who develop a five o'clock shadow after having shaved their faces. Hair_sentence_177

This new growth is called stubble. Hair_sentence_178

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. Hair_sentence_179

Waxing Hair_section_22

Waxing involves using a sticky wax and strip of paper or cloth to pull hair from the root. Hair_sentence_180

Waxing is the ideal hair removal technique to keep an area hair-free for long periods of time. Hair_sentence_181

It can take three to five weeks for waxed hair to begin to resurface again. Hair_sentence_182

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. Hair_sentence_183

Laser removal Hair_section_23

Main article: Laser hair removal Hair_sentence_184

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. Hair_sentence_185

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. Hair_sentence_186

Laser removal is practiced in many clinics along with many at-home products. Hair_sentence_187

Cutting and trimming Hair_section_24

See also: Ponytail Hair_sentence_188

Because the hair on one's head is normally longer than other types of body hair, it is cut with scissors or clippers. Hair_sentence_189

People with longer hair will most often use scissors to cut their hair, whereas shorter hair is maintained using a trimmer. Hair_sentence_190

Depending on the desired length and overall health of the hair, periods without cutting or trimming the hair can vary. Hair_sentence_191

Cut hair may be used in wigs. Hair_sentence_192

Global imports of hair in 2010 was worth $US 1.24 billion. Hair_sentence_193

Social role Hair_section_25

See also: Hairstyle Hair_sentence_194

Hair has great social significance for human beings. Hair_sentence_195

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_sentence_196

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. Hair_sentence_197

These include the face, ears, head, eyebrows, legs, and armpits, as well as the pubic region. Hair_sentence_198

The highly visible differences between male and female body and facial hair are a notable secondary sex characteristic. Hair_sentence_199

The world's longest documented hair belongs to Xie Qiuping (in China), at 5.627 m (18 ft 5.54 in) when measured on 8 May 2004. Hair_sentence_200

She has been growing her hair since 1973, from the age of 13. Hair_sentence_201

Indication of status Hair_section_26

Healthy hair indicates health and youth (important in evolutionary biology). Hair_sentence_202

Hair color and texture can be a sign of ethnic ancestry. Hair_sentence_203

Facial hair is a sign of puberty in men. Hair_sentence_204

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). Hair_sentence_205

Male pattern baldness is a sign of age, which may be concealed with a toupee, hats, or religious and cultural adornments. Hair_sentence_206

Although drugs and medical procedures exist for the treatment of baldness, many balding men simply shave their heads. Hair_sentence_207

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. Hair_sentence_208

Hairstyle may be an indicator of group membership. Hair_sentence_209

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. Hair_sentence_210

This led to the Parliamentary faction being nicknamed Roundheads. Hair_sentence_211

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. Hair_sentence_212

Having bobbed hair was popular among the flappers in the 1920s as a sign of rebellion against traditional roles for women. Hair_sentence_213

Female art students known as the "cropheads" also adopted the style, notably at the Slade School in London, England. Hair_sentence_214

Regional variations in hirsutism cause practices regarding hair on the arms and legs to differ. Hair_sentence_215

Some religious groups may follow certain rules regarding hair as part of religious observance. Hair_sentence_216

The rules often differ for men and women. Hair_sentence_217

Many subcultures have hairstyles which may indicate an unofficial membership. Hair_sentence_218

Many hippies, metalheads, and Indian sadhus have long hair, as well many older indie kids. Hair_sentence_219

Many punks wear a hairstyle known as a mohawk or other spiked and dyed hairstyles; skinheads have short-cropped or completely shaved heads. Hair_sentence_220

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. Hair_sentence_221

Heads were shaved in concentration camps, and head-shaving has been used as punishment, especially for women with long hair. Hair_sentence_222

The shaven head is common in military haircuts, while Western monks are known for the tonsure. Hair_sentence_223

By contrast, among some Indian holy men, the hair is worn extremely long. Hair_sentence_224

In the time of Confucius (5th century BCE), the Chinese grew out their hair and often tied it, as a symbol of filial piety. Hair_sentence_225

Regular hairdressing in some cultures is considered a sign of wealth or status. Hair_sentence_226

The dreadlocks of the Rastafari movement were despised early in the movement's history. Hair_sentence_227

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. Hair_sentence_228

Cutting the hair also may be a sign of mourning. Hair_sentence_229

Tightly coiled hair in its natural state may be worn in an Afro. Hair_sentence_230

This hairstyle was once worn among African Americans as a symbol of racial pride. Hair_sentence_231

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. Hair_sentence_232

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. Hair_sentence_233

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. Hair_sentence_234

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. Hair_sentence_235

During the appeal trial, they appeared in the dock wearing wigs. Hair_sentence_236

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. Hair_sentence_237

Religious practices Hair_section_27

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. Hair_sentence_238

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. Hair_sentence_239

Orthodox Judaism also commands the use of scarves and other head coverings for married women for modesty reasons. Hair_sentence_240

Certain Hindu sects also wear head scarves for religious reasons. Hair_sentence_241

Sikhs have an obligation not to cut hair (a Sikh cutting hair becomes 'apostate' which means fallen from religion) and men keep it tied in a bun on the head, which is then covered appropriately using a turban. Hair_sentence_242

Multiple religions, both ancient and contemporary, require or advise one to allow their hair to become dreadlocks, though people also wear them for fashion. Hair_sentence_243

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. Hair_sentence_244

Some Christian sects throughout history and up to modern times have also religiously proscribed the cutting of women's hair. Hair_sentence_245

For some Sunni madhabs, the donning of a kufi or topi is a form of sunnah. Hair_sentence_246

See also Hair_section_28

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Hair.