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| − | {{articleissues|article=y|refimprove=December 2007|expert=Anatomy}}
| + | '''Hair''' is the name for the covering of keratin fiber found in most [[mammals]]. Human hair types are produced by a mixture of genetics and the effects of [[magnetic]] interaction during early development<ref>John Gray, Human Hair Diversity</ref>. [[Image:Samson.jpg|right]] |
| − | {{2otheruses|the body feature|the stage production|Hair (musical)|the film|Hair (film)}}
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| − | [[Image:Menschenhaar 200 fach.jpg|300px|thumb|Human hair under 200-times magnification]]
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| − | '''Hair''' is an outgrowth of protein, found only on [[mammals]].<ref> [http://www.askoxford.com/concise_oed/hair?view=uk definition] askoxford.com</ref> It projects from the [[epidermis (skin)|epidermis]], though it grows from [[hair follicle]]s deep in the [[dermis]]. Although many other organisms, especially [[insects]], show filamentous outgrowths, these are not considered "hair". So-called "hairs" ([[trichome]]s) are also found on [[plant]]s. The projections on [[arthropod]]s such as [[insect]]s and [[spider]]s are actually insect [[bristle]]s, composed of a [[polysaccharide]] called [[chitin]]. The hair of non-human mammal [[species]] is commonly referred to as [[fur]]. There are varieties of [[cat]]s, [[dog]]s, and [[mouse|mice]] bred to have little or no visible fur. In some species, hair is absent at certain stages of life. The main component of hair fiber is [[keratin]]. Keratins are [[protein]]s: long chains ([[polymer]]s) of [[amino acid]]s. | |
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| − | == Body hair == | + | ==References== |
| − | {{Human hair}}
| + | <references/> |
| − | [[Image:Human hair closeup-08960-nevit.jpg|thumb|Close-up of human hair]]
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| − | Historically, several ideas have been advanced to explain the small amount of [[body hair]] in humans, as compared to other species. Many were faced with the same problem that there is no fossil record of human hair to back up the conjectures nor to determine exactly when this feature evolved. However, recent research on the evolution of lice suggests that human ancestors lost their body hair approximately 3.3 million years ago. <ref>Wade, N. (2007). In Lice, Clues to Human Origin and Attire. ''[[New York Times]]'', ''156''(53877), A17.</ref>
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| − | [[Savanna theory]] suggests that nature selected humans for shorter and thinner body hair as part of a set of adaptations to the warm plains of the savanna, including bipedal locomotion and an upright posture. There are several problems (including balding) with this theory, not least of which is that [[cursorial hunting]] is used by other animals that do not show any thinning of hair.
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| − | Another theory for the thin [[body hair]] on humans proposes that [[Fisherian runaway]] [[sexual selection]] played a role here (as well as in the selection of long head hair). Possibly this occurred in conjunction with [[neoteny]], with the more juvenile appearing females being selected by males as more desirable (see [[#Types of hair|types of hair]] and [[vellus hair]]).
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| − | Another theory is the possible co-evolution of man with a very early use of [[clothing]], especially in colder northern climates, after the [[Hominina]] came out of Africa.
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| − | The [[aquatic ape hypothesis]] posits that sparsity of hair is an adaptation to an aquatic environment, but it has little support amongst scientists and very few aquatic mammals are, in fact, hairless.
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| − | In reality, there may be little to explain. Humans, like all primates, are part of a trend toward sparser hair in larger animals; the ''density'' of human hair follicles on the skin is actually about what one would expect for an animal of equivalent size<ref>Shwartz, G. G. & Rosenblum, L. A. (?). Allometry of primate hair density and the evolution of human hairlessness. ''American Journal of Physical Anthropology'', ''55''(1), pp. ??</ref>. The outstanding question is why so much of human hair is short, underpigmented [[vellus hair]], rather than [[terminal hair]].
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| − | == Characteristics ==
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| − | [[Image:Edward S. Curtis Collection People 043.jpg|left|thumb|Traditional [[Hopi]] hair style, photo by [[Edward S. Curtis]], 1922]]
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| − | === Types of hair ===
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| − | Human beings have three different types of hair:
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| − | * [[Lanugo]], the fine hair that covers nearly the entire body of [[fetus]]es.
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| − | * [[Vellus hair]], the short, fine, "peach fuzz" body hair that grows in most places on the human body in both sexes.
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| − | * [[Terminal hair]], the fully developed hair, which is generally longer, coarser, thicker, and darker than vellus hair.
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| − | ===Texture===
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| − | Hair [[Texture (crystalline)|texture]] is described as ''fine'', ''medium'', ''coarse'' or ''wiry'', depending on the hair diameter. Within the four texture ranges hair can also be thin, medium or thick density and it can be straight, curly or wavy. [[Hair conditioner]] also affects hair texture. Hair can be healthy, normal, oily, dry, damaged or a combination. Hair texture can also be affected by hair styling equipment such as [[straighteners]], crimpers, or [[curlers]]. Also, a [[hairdresser]] can change hair texture with chemicals.
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| − | Hair is genetically programmed to be straight, curly or wavy, and it can change over time.
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| − | For many years, it was believed that the shape of a person’s hair was determined by the individual hair shafts, and that curly hair was curly because the cross-section of the hair shaft was flatter and had more intertwined layers than straight hair, which was round. But scientists have determined that whether your hair is curly or straight is determined by the shape of the follicle itself and the direction in which each strand grows out of its follicle. Curly hair is shaped like an elongated oval and grows at a sharp angle to the scalp.
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| − | Curly hair has a different biological structure from straight hair. It tends to be much drier than straight hair because the oils secreted into the hair shaft by the [[sebaceous gland]]s can more easily travel down the shaft of straight hair. People with very curly hair may find that this hair type can be dry and often frizzy.
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| − | Hair, whether it is curly or straight, is affected by the amount of humidity in the air. It serves as a restoring force for the hair, forcing water back into the hair fiber and forcing hair shaft to return to its original structure. This may be more noticeable in somebody with curly hair because it tends to get frizzy when the humidity rises.
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| − | Hair texture variation is likely to have resulted from a significant event in human evolutionary history. Evolutionary biologists agree that the evidence suggests that genus Homo arose in East Africa approximately 2 million years ago. During this time body size increased in response to richer dietary intake. This increase was most likely a reflection of rapidly increasing brain size among members of this genus, which facilitated an increasing intellectual capacity that made more varied dietary access possible (i.e. via new hunting and scavenging techniques etc.). Jablonski et al. (2004) postulate that as body size increase, it became evolutionarily necessary to expel heat from the body at a more rapid rate. As a result, humans developed the ability to sweat. They also lost body hair in order to facilitate sweat evaporation and hence cooling of the body.
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| − | === Aging ===
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| − | Older people tend to develop grey hair because their hair follicles produce less [[pigment]] and the hair becomes colorless. Grey hair is considered to be a characteristic of normal aging. The age at which this occurs varies from person to person, but in general nearly everyone 75 years or older has grey hair, and in general men tend to become grey at younger ages than women.
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| − | It should be noted however, that grey hair in itself is not actually grey; the grey head of hair is a result of a combination of the dark and white/colourless hair forming an overall 'grey' appearance to the observer. As such, people starting out with very pale [[blond]] hair usually develop white hair instead of grey hair when aging. Red hair usually doesn't turn grey with age; rather it becomes a sandy colour and afterward turns white. Some degree of [[scalp]] [[hair loss]] or thinning generally accompanies ageing in both males and females, and it's estimated that half of all men are affected by [[Androgenic alopecia|male pattern baldness]] by the time they are 50<ref name="halfofmen">[http://nl.newsbank.com/nl-search/we/Archives?s_site=ozarksnow&f_site=ozarksnow&f_sitename=Springfield+News-Leader+%28MO%29&p_theme=gannett&p_product=SNLB&p_action=search&p_field_base-0=&p_text_base-0=baldness&Search=Search&p_perpage=10&p_maxdocs=200&p_queryname=700&s_search_type=keyword&p_sort=_rank_%3AD&p_field_date-0=YMD_date&p_params_date-0=date%3AB%2CE&p_text_date-0= "Uncovering the bald truth about hair loss."] ''Springfield News-leader'', May 10, 2005. "Half of men" estimate is made by the American Academy of Dermatology and specifically estimates prevalence in the U.S. population, though this should reflect prevalence in other populations.</ref>. The tendency toward [[baldness]] is a trait shared by a number of other [[primate]] [[species]], and is thought to have evolutionary roots.
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| − | It is commonly claimed that hair and nails will continue growing for several days after death. This is a myth; the appearance of growth is actually caused by the retraction of skin as the surrounding tissue [[dehydrate]]s, making nails and hair more prominent.
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| − | === Pathological impacts on hair ===
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| − | [[Drugs]] used in [[cancer]] [[chemotherapy]] frequently cause a temporary loss of hair, noticeable on the [[head]] and [[eyebrow]]s, because they kill all rapidly dividing [[cell (biology)|cell]]s, not just the cancerous ones. Other [[disease]]s and [[Physical trauma|trauma]]s can cause temporary or permanent loss of hair, either generally or in patches. Patients with Hyperthyriodism or Hypothyriodism can experience hair loss until their hormone levels are regulated.
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| − | The hair shafts may also store certain [[poison]]s for years, even decades, after death. In the case of Col. [[Lafayette Baker]], who died [[July 3]], [[1868]], use of an [[atomic]] [[Absorption (electromagnetic radiation)|absorption]] [[spectrophotometer]] showed the man was killed by white [[arsenic]]. The prime suspect was [[Wally Pollack]], Baker's brother-in-law. According to Dr. Ray A. Neff, Pollack had laced Baker's [[beer]] with it over a period of months, and a century or so later minute traces of arsenic showed up in the dead man's hair. Mrs. Baker's [[diary]] seems to confirm that it was indeed arsenic, as she writes of how she found some vials of it inside her brother's suitcoat one day.
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| − | === Width ===
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| − | According to ''The [[Physics]] Factbook'', the [[diameter]] of human hair ranges from 17 to 181 [[micrometre|µm]].<ref>{{cite web|url=http://hypertextbook.com/facts/1999/BrianLey.shtml|title=Width of a Human Hair|last=Ley|first=Brian|work=The Physics Factbook|year=1999}}</ref>
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| − | == Hair care and hair loss ==
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| − | {{Main|Hair care|Baldness|Baldness treatments}}
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| − | == Cultural attitudes ==
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| − | === Head hair ===
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| − | [[Image:Hair.jpg|right|thumb|120px|People from different cultures have invented various ways to arrange, or "style" their hair.]]
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| − | The remarkable head hair of humans has gained an important significance in nearly all present societies as well as any given historical period throughout the world. The [[haircut]] has always played a significant [[cultural]] and [[social role of hair|social role]].
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| − | In [[ancient Egypt]] head hair was often shaved, especially amongst children, as long hair was uncomfortable in the heat. Children were often left with a long lock of hair growing from one part of their heads, the practice being so common that it became the standard in Egyptian art for artists to depict children as always wearing this "sidelock". Many adult men and women kept their heads permanently shaved for comfort in the heat and to keep the head free of [[lice]], while wearing a [[Wig (hair)|wig]] in public.
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| − | In [[ancient Greece]], [[ancient India]] and [[ancient Rome]] men and women already differed from each other through their haircuts. The head hair of women was long and pulled back into a [[Chignon (hairstyle)|chignon]]. Many dyed their hair red with [[henna]] and sprinkled it with [[gold]] powder, often adorning it with fresh flowers. Men’s hair was short and even occasionally shaved. In Rome [[hairdressing]] became ever more popular and the [[upper class]]es were attended to by [[slavery|slave]]s or visited public [[barber]] shops.
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| − | [[Image:Maasai tribe.jpg|left|thumb|250px|Maasai warriors with their traditional hair styling]]
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| − | <!-- The tradition of women having [[long hair]] and men having short hair is usually traced back to times of war, where having long hair meant that one was weak and was to be spared. Generally men, being viewed as strong and dominant, would cut their hair short, while women who were considered inferior and weaker, would keep their hair long so that they would be spared. -->
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| − | The traditional hair styling in some parts of [[Africa]] also gives interesting examples of how people dealt with their head hair. The [[Maasai]] [[warrior]]s tied the front hair into sections of tiny [[braid]]s while the back hair was allowed to grow to waist length. Women and non-warriors, however, shaved their heads. Many tribes dyed the hair with red earth and [[Fat|grease]]; some stiffened it with [[animal]] [[Cow dung|dung]].
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| − | Contemporary social and cultural conditions have constantly influenced popular hair styles. From the 17th century into the early 19th century it was the norm in [[Western culture]] for men to have long hair often tied back into a [[ponytail]]. Famous long-haired men include [[René Descartes]], [[Giacomo Casanova]], [[Oliver Cromwell]] and [[George Washington]]. During his younger years [[Napoleon Bonaparte]] had a long and flamboyant head of hair. Before [[World War I]] men generally had longer hair and [[beard]]s. The [[trench warfare]] between 1914 and 1918 exposed men to [[lice]] and [[flea]] [[infestation]]s, which prompted the order to cut hair short, establishing a norm that has persisted.
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| − | It has also been advanced that short hair on men has been enforced as a means of control, as shown in the military and police and other forces that require obedience and discipline. Additionally, slaves and defeated armies were often required to shave their heads, in both pre-[[medieval]] [[Europe]] and [[China]].
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| − | Long hair was almost universal among women in [[Western culture]] until [[World War I]]. Many women in conservative [[Pentecostal]] groups abstain from trimming their hair after conversion (and some have never had their hair trimmed or cut at all since birth). The social revolution of the 1960s led to a renaissance of unchecked hair growth. Hair length is measured from the front [[scalp]] line on the [[forehead]] up over the top of the head and down the back to the floor. Standard milestones in this process of hair growing are [[waist]] length, [[hip]] length, classic length (midpoint on the body, where the [[buttock]]s meet the [[thigh]]s), [[thigh]] length, knee length, ankle length and even beyond. It takes about seven years, including occasional trims, to grow one's hair to waist length. Terminal length varies from person to person according to [[genetics]] and overall health.
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| − | A thriving salon culture in [[Detroit]] gave rise to the Detroit [[Hair Wars]] in 1991. Using the medium of human and synthetic hair, elaborate fantastical head pieces, such as spider webs, flowers and flying "hair-y copters", have been made by participants.[http://www.metrotimes.com/editorial/story.asp?id=6098]
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| − | === Body hair ===
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| − | [[Image:Mark Twain-Shirtless-ca1883.jpg|thumb|[[Mark Twain]], Shirtless. A human male with body hair.]]
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| − | The attitudes towards hair on the human body also vary between different cultures and times. In some cultures profuse [[chest hair]] on men is a symbol of [[virility]] and [[masculinity]]; other societies display a hairless body as a sign of youthfulness.
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| − | In [[ancient Egypt]], people regarded a completely smooth, hairless body as the standard of [[beauty]]. An upper class Egyptian woman took great pains to ensure that she did not have a single hair on her body, except for the top of her head (and even this was often replaced with a wig<ref name="Egypt">Dersin, Denise, et al. (Eds.) (1996). ''What Life Was Like On the Banks of the Nile''. Richmond, Virginia: Time-Life Books.</ref>). The [[ancient Greece|ancient Greeks]] later adopted this smooth ideal, considering a hairless body to be representative of [[youth]] and beauty. This is reflected in Greek female sculptures which do not display any [[pubic hair]]. [[Islam]] stipulates many tenets with respect to hair, such as the covering of hair by women and the removal of armpit and pubic hair (see [[fitrah|five physical characteristics traits of fitrah]]).
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| − | === Hair as business factor ===
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| − | [[Hair care]] for humans is a major world industry with specialized tools, chemicals and techniques. The business of various products connected with human hair has become an important industrial and financial factor in [[Western societies]].
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| − | ==Social role of hair==
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| − | {{Prose|date=February 2008}}
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| − | [[Hair]] has great social significance for [[human being]]s. It can grow on most areas of the [[human body]], except on the palms of the [[hand]]s and the soles of the [[foot|feet]] (among other areas), but hair is most noticeable in most people in a small number of areas, which are also the ones that are most commonly trimmed, plucked, or [[shave]]d. These include the [[face]], [[nose]], [[ears]], [[head (anatomy)|head]], [[eyebrow]]s, [[eyelash]]es, [[leg]]s and [[armpit]]s, as well as the [[pubic region]]. The highly visible differences between male and female body and facial hair are a notable [[secondary sex characteristic]].
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| − | [[Image:Allori Portrait.jpg|thumb|right|250px|''Portrait of a Woman,'' Alessandro Allori (1535 - 1607; [[Uffizi Gallery]]): a plucked hairline gives a fashionably "noble brow"]]
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| − | === Hair as indicator ===
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| − | * Healthy hair indicates health and youth (important in [[evolutionary biology]])
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| − | * Hair colour and texture can be a sign of ethnic ancestry
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| − | * [[Facial hair]] is a sign of [[puberty]] in men
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| − | * White hair is a sign of age, which can be concealed with [[hair dye]]
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| − | * Male pattern [[baldness]] is sign of age, which can be concealed with a [[toupee]], hats or religious/cultural adornments. In modern times, it can be reversed in some men with [[minoxidil]] (marketed as [[Rogaine (drug)|Rogaine]] or Regaine) or [[finasteride]] (marketed as Propecia); see [[Baldness treatments]]
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| − | * [[Hairstyle]] can be an indicator of group membership:
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| − | ** [[Metalhead]] long-hair for headbanging, also symbolic of a metalhead belonging to the metal world.
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| − | ** Beatle "pudding-bowl" haircuts
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| − | ** Punk [[Mohawk Hairstyle|mohawk]] haircuts
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| − | ** [[Skinhead]] haircut
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| − | ** [[Mullet (haircut)|Mullet]] hairstyle
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| − | ** [[Deathhawk]] A larger, fuller version of a mohawk - popular in the [[gothic sub-culture]]
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| − | ** [[Undercut]] where the sides and back of the head are shaved short or bald, and the top hair is allowed to grow long. Common with metalheads and in the [[Cyber (subculture)|Cybergoth subculture]], especially with women, although it is accepted as a unisex hair style.
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| − | ** "[[Emo]]" hair where the bangs cover one eye
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| − | ** [[Fascinator]] where the hair is short at the back and long at the front and the front forms itself into a point. It is similar to a mullet in reverse (also known as a frullet).
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| − | * Some groups, for example [[Sikh]]s and male [[orthodox Jew]]s, never cut or shave some or all of their hair.
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| − | * Some groups, such as women in the [[Muslim]] and [[orthodox Jewish]] communities, cover their hair as part of religious observance.
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| − | * It is found that [[hair whorl]] is associated with [[neural development|brain development]].
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| − | === Growing and removing ===
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| − | * Hair length for men: [[Cavalier]]s and [[Roundhead]]s, long hair in the [[1960s]], [[skinhead]]s, [[Mullet (haircut)|mullet]]s and other hairstyles, the uncut hair of [[Sikh]]s.
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| − | * Women with short hair are often looked at as lesbians.
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| − | ** The ''bobbed'' hair of [[flapper]]s
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| − | * Hairy arms and legs, regional variations in [[hirsutism]]
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| − | ===Hair, power, punishment, and status===
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| − | [[Image:Hair-punishment.jpg|thumb|300px|right|[[France|French]] civilians shave the head of a young woman as punishment for wartime collaboration, [[August 29]] [[1944]]]]
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| − | * [[Samson]] and [[Delilah]]
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| − | * Shaved heads in [[concentration camp]]s
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| − | * Head-shaving as [[punishment]] - especially for women with long hair.
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| − | *[[Military]] haircuts, monastic [[tonsure]]s
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| − | * [[Kovstro]] and his Seven Hounds
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| − | * Extremely long hair of some Indian holy men
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| − | * Regular hairdressing as sign of wealth
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| − | * The [[dreadlocks]] of the [[Rastafari movement]]
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| − | * Own removal of hair in order to [[liberate]] oneself from their past, usually after a trying time in one's life.
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| − | * Tightly curled [[Afro]]s are sometimes worn among Blacks as a symbol of racial pride
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| − | *[[Flappers]] of the [[1920s]] cut their traditional long hair into short [[Bob cut]]s to show their independence and sexual freedom.
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| − | *[[Hippie]]s of the [[1960s]] grew their hair long in order to illustrate their distance from mainstream society. The film ''[[Easy Rider]]'' ([[1969]]) includes the description of one [[Hippie]] forcibly having his head shaved with a rusty razor to indicate the intolerance of some conservative groups towards the [[Hippie]] movement.
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| − | === Concealing and revealing ===
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| − | * Keeping women's hair hidden: [[headscarf|headscarves]], the ''[[hijab]]'' in [[Islam]], [[head-shaving]] and wigs in [[Orthodox Judaism]] etc.
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| − | * Keeping men's hair hidden: the [[turban]] in [[Sikhism]]
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| − | * Displaying women's hair: hair fashions in Western society
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| − | * Displaying men's hair: [[facial hair]] in Islam, ringlets in [[Hassidic Judaism]]
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| − | * Hair ornaments
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| − | * Keeping [[pubic hair]] hidden or shaven
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| − | ==See also==
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| − | *[[Hypotrichosis]], the state of having a less than normal amount of hair on the head or body
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| − | == References ==
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| − | {{Reflist}}
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| − | ==External links==
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| − | {{wiktionary|hair}}
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| − | *[http://answers.google.com/answers/threadview?id=122411 Discussion about shaving and cultures]
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| − | *[http://www.scribd.com/doc/2463/Curious-about-Nails-and-Hairs/ Answers to several questions related to hair from curious kids]
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| − | *[http://www.fysikbasen.dk/English.php?page=HairMeasure How to measure the diameter of your own hair using a laser pointer]
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| − | *[http://www.rsc.org/Publishing/Journals/cb/Volume/2007/7/hair_is_the_news.asp Instant insight] outlining the chemistry of hair from the [[Royal Society of Chemistry]]
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| − | *[http://www.amazon.com/Fur-Imaginary-Portrait-Diane-Arbus/dp/B000NO1XG8 About Fur: An Imaginary Portrait of Diane Arbus],the recent film which describes only a part of the life and work of the photographer, particularly her relationship to a man who was born with a peculiarly hair-covered skin
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| − | {{integumentary_system}}
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| − | {{human anatomical features}}
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| − | [[Category:Hair| ]]
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| − | [[Category:Integumentary system]]
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| − | [[Category:Animal hair]]
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| − | [[Category:Anthropology]]
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| − | [[Category:Sociology]]
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