View source for Hair

{{short description|Protein filament that grows from follicles found in the dermis, or skin}}
{{About|hair in humans and other mammals|hairs in other organisms|Seta|and|Trichome|other uses|Hair (disambiguation)}}
{{protection padlock|small=yes}}
{{Use dmy dates|date=October 2021}}
{{Infobox anatomy
| Name        = Hair
| Latin       = capillum
| Image       = Gray945.png
| Caption     = Cross section of a human hair strand
| Width       = 
| Image2      = File:CSIRO ScienceImage 8115 Human hair and Merino wool fibre.jpg
| Caption2    = [[Scanning electron microscopy]] image of [[Merino]] wool (top) and human hair (bottom) showing keratin scales
| Precursor   = 
| System      = [[Integumentary system]]
| Artery      = 
| Vein        = 
| Nerve       = 
| Lymph       = 
}}

'''Hair''' is a [[protein filament]] that grows from [[hair follicle|follicles]] found in the [[dermis]]. Hair is one of the defining characteristics of [[mammal]]s.
The [[human body]], apart from areas of [[glabrous]] [[skin]], is covered in follicles which produce thick [[terminal hair|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 [[hairstyle]]s 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, [[Gender identity|gender]], or [[religion]].<ref>{{cite book|last=Sherrow|first=Victoria|title=Encyclopedia of Hair: A Cultural History|year=2006|publisher=Greenwood Press|location=Westport, CT|isbn=978-0-313-33145-9|page=iv|url=https://archive.org/details/encyclopediaofha0000sher}}</ref>

==Overview==
===Meaning===
[[File:506 Hair.jpg|thumb|Anatomy of the hair shaft and bulb.]]
The word "hair" usually refers to two distinct structures: 
#the part beneath the skin, called the [[hair follicle]], or, when pulled from the skin, the bulb or root. This organ is located in the [[dermis]] and maintains [[stem cell]]s, which not only re-grow the hair after it falls out, but also are recruited to regrow skin after a [[wound]].<ref>{{cite journal|last1= Krause|first1= K|last2= Foitzik|first2= K|title= Biology of the Hair Follicle: The Basics|journal= Seminars in Cutaneous Medicine and Surgery|volume= 25|issue= 1|pages= 2–10|year= 2006|doi= 10.1016/j.sder.2006.01.002|doi-broken-date= 12 July 2025|pmid= 16616298| issn=1085-5629}}</ref>
# the hair shaft, which is the hard filamentous part that extends above the skin surface. It is made of multi-layered keratinized (dead) flat cells whose rope-like filaments provide structure and strength to it. The protein called [[keratin]] makes up most of its volume. A cross section of the hair shaft may be divided roughly into three zones.

Hair fibers have a structure consisting of several layers, starting from the outside:
# the [[Cuticle (hair)|cuticle]], which consists of several layers of flat, thin cells laid out overlapping one another as roof shingles
# the [[Cortex (hair)|cortex]], which contains the [[keratin]] bundles in cell structures that remain roughly rod-like
# the [[Medulla (hair)|medulla]], a disorganized and open area at the fiber's center<ref>{{cite book|author=Feughelman, Max|url=https://books.google.com/books?id=PSNIYKwKu8kC|title=Mechanical Properties and Structure of Alpha-keratin Fibres: Wool, Human Hair and Related Fibres|publisher=UNSW Press|year=1997|isbn=978-0-86840-359-5|access-date=27 January 2016}}</ref>

===Etymology===
The word "hair" is derived from {{langx|enm|heer}} and {{lang|enm|hêr}}, in turn derived from {{langx|ang|hǽr}} and {{lang|ang|hér}}, with influence from {{langx|non|hár}}. Both the Old English and Old Norse words derive from {{langx|gem-x-proto|hēran}} and are related to terms for hair in other Germanic languages such as {{langx|sv|hår}}, [[Dutch language|Dutch]] and {{langx|de|haar}}, and {{langx|ofs|her}}.<ref>{{cite web |title=hair - Etymology of hair by etymonline |url=https://www.etymonline.com/word/hair#etymonline_v_1377 |website=www.etymonline.com |language=en|access-date=20 July 2024}}</ref><ref>{{cite web |title=hair |url=https://www.oed.com/dictionary/hair_n?tab=factsheet#2190694 |website=OED |access-date=20 July 2024}}</ref> The now broadly obsolete word "fax" refers specifically to head hair and is found in compounds such as [[Fairfax (name)|Fairfax]] and [[Halifax, West Yorkshire|Halifax]]. It is derived from {{langx|ang|feax}} and is cognate with terms such as [[Old Norse]] and {{langx|no|fax}}.<ref>{{cite web |title=fax |url=https://www.oed.com/dictionary/fax_n1?tab=factsheet |website=OED |access-date=20 July 2024}}</ref>

== Description ==
[[File:Hair follicle of feline - Microscopic view 2.jpg|thumb|[[Hair follicle]] of [[Felidae]].]]

Each strand of hair is made up of the [[Medulla (hair)|medulla]], [[Cortex (hair)|cortex]], and [[Cuticle (hair)|cuticle]].<ref name="Hair Structure and Hair Life Cycle">[https://web.archive.org/web/20110303132725/http://www.follicle.com/hair-structure-life-cycle.html Hair Structure and Hair Life Cycle]. follicle.com</ref> The innermost region, the [[Medulla (hair)|medulla]], is an open and unstructured region that is not always present.<ref name="Topic 2: The Layers of the Hair">{{cite web |url=http://www.texascollaborative.org/hildasustaita/module%20files/topic2.htm |title=Topic 2 |publisher=Texascollaborative.org |access-date=18 February 2015 |archive-url=https://archive.today/20130415220704/http://www.texascollaborative.org/hildasustaita/module%20files/topic2.htm |archive-date=15 April 2013 |url-status=dead }}</ref> The highly structural and organized [[Cortex (hair)|cortex]], or second of three layers of the hair, is the primary source of mechanical strength and water uptake. The cortex contains [[melanin]], which colors the [[fiber]] based on the number, distribution and types of [[melanin]] granules. The melanin may be evenly spaced or cluster around the edges of the hair.<ref name=bisbing>{{cite book |first=Richard E. |last=Bisbing |chapter=3. The Forensic Identification and Association of Human Hair |title=Forensic Science Handbook |volume=1 |editor-first1=Richard |editor-last1=Saferstein |editor-first2=Adam B. |editor-last2=Hall |edition=3rd |publisher=[[CRC Press]] |pages=[https://books.google.com/books?id=pDsPEAAAQBAJ&pg=PA165 165]-[https://books.google.com/books?id=pDsPEAAAQBAJ&pg=PA166 166] }} Archived (pp. [https://web.archive.org/web/20230418032945/https://books.google.com/books?id=pDsPEAAAQBAJ&pg=PA165#v=onepage&q&f=false 165], [https://web.archive.org/web/20230418032957/https://books.google.com/books?id=pDsPEAAAQBAJ&pg=PA166#v=onepage&q&f=false 166]) on 18 April 2023.</ref> 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.<ref name="Hair Structure and Hair Life Cycle"/> The diameter of human hair varies from {{convert|0.017|to|0.18|mm|sp=us|lk=in}}.<ref>{{cite web|last=Ley|first=Brian|year=1999|title=Diameter of a Human Hair|url=http://hypertextbook.com/facts/1999/BrianLey.shtml|access-date=28 June 2010}}</ref> Some of these characteristics in humans' head hair vary by race: people of mostly African ancestry tend to have hair with a diameter of 60–90 [[μm]] and a flat cross-section, while people of mostly European or Middle Eastern ancestry tend to have hair with a diameter of 70–100 [[μm]] and an oval cross-section, and people of mostly Asian or Native American ancestry tend to have hair with a diameter of 90–120 [[μm]] and a round cross-section.<ref name=bisbing/> There are roughly two million small, tubular glands and [[sweat gland]]s 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.<ref>{{cite book |title=Disease and Its Causes |chapter-url=https://archive.org/details/b28112325 |year=1913 |publisher=New York Henry Holt and Company London Williams and Norgate The University Press, Cambridge, USA |location=United States |author=Councilman, W. T. |chapter=Ch. 1}}</ref>

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.<ref>{{cite book |editor1=Freinkel, R.K. |editor2=Woodley, D.T. |title=The Biology of the Skin |date=15 March 2001 |publisher=[[CRC Press]] |isbn=9781850700067 |page=80}}</ref> 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===
{{Infobox anatomy
| Name        = Root of the hair
| Latin       = radix pili
| Image       = Gray944.png
| Caption     = Section of [[skin]], showing the [[Epidermis (skin)|epidermis]] and [[dermis]]; a hair in its follicle; the [[arrector pili]] muscle; [[sebaceous glands]].
| Image2      = 
| Caption2    = 
| System      = 
| Precursor   = 
}}
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 (skin)|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.<ref>[http://www.histology.leeds.ac.uk/skin/hair.php Histology Guide | Skin] Histology.leeds.ac.uk. Retrieved on 18 May 2016.</ref>

===Natural color===
{{main|Human hair color}}
[[File:Hair Autofluorescence.jpg|thumb|Human hair contains melanin which provides dark coloration and protection from UV radiation. Human hair can absorb and emit light across a wide range of wavelengths. The image above depicts melanin autofluorescence at 365-400 nm excitation from a strand of dark brown human hair.]]
[[File:Brown hair.jpg|thumb|A girl with reddish brown hair]]
All natural hair colors are the result of two types of hair pigments. Both of these pigments are melanin types, produced inside the hair follicle and packed into granules found in the fibers. [[Eumelanin]] is the dominant pigment in [[brown hair]] and [[black hair]], while [[pheomelanin]] is dominant in [[red hair]]. [[Blond hair]] is the result of having little [[pigmentation]] in the hair strand. [[Gray hair]] occurs when melanin production decreases or stops, while [[poliosis]] is white hair (and often the skin to which the hair is attached), typically in spots that never possessed melanin at all, or ceased for natural reasons, generally genetic, in the first years of life.

===Human hair growth===
{{main|Human hair growth}}
Hair grows everywhere on the external body except for [[mucous membranes]] and glabrous skin, such as that found on the palms of the hands, soles of the feet, and lips. 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.

[[File:Hair-follicle cycling.ogv|thumb|Hair-follicle cycling]]
[[File:Blond long-haired young lady woman.jpg|thumb|Hair grows at different speeds and different lengths. Its composition causes different colors and textures, which influence how long the hair strands grow.]]
[[File:Marianne Ernst, Long hair model.jpg|thumb|Marianne Ernst, a German "Long hair model".]]
The three stages of hair growth are the [[Hair follicle#Anagen phase|anagen]], [[Hair follicle#Catagen phase|catagen]], and [[Hair follicle#Telogen phase|telogen]] phases. Each strand of hair on the human body is at its own stage of development. Once the cycle is complete, it restarts and a new strand of hair begins to form. The growth rate of hair varies from individual to individual depending on their age, genetic predisposition and a number of environmental factors.<ref>{{Cite journal|last1=Schneider|first1=Marlon R.|last2=Schmidt-Ullrich|first2=Ruth|last3=Paus|first3=Ralf|date=2009-02-10|title=The hair follicle as a dynamic miniorgan|journal=Current Biology|volume=19|issue=3|pages=R132–142|doi=10.1016/j.cub.2008.12.005|issn=1879-0445|pmid=19211055|doi-access=free|bibcode=2009CBio...19.R132S }}</ref> It is commonly stated that hair grows about 1&nbsp;cm per month on average; however reality is more complex, since not all hair grows at once. Scalp hair was reported to grow between 0.6&nbsp;cm and 3.36&nbsp;cm per month. The growth rate of scalp hair somewhat depends on age (hair tends to grow more slowly with age), sex, and ethnicity.<ref name=Harkey>{{Cite journal|last=Harkey|first=M. R.|date=December 1993|title=Anatomy and physiology of hair|journal=Forensic Science International|series=Hair Analysis as a Diagnostic Tool for Drugs of Abuse Investigation|volume=63|issue=1|pages=9–18|doi=10.1016/0379-0738(93)90255-9|pmid=8138238|issn=0379-0738}}</ref> Thicker hair (>60&nbsp;μm) grows generally faster (11.4&nbsp;mm per month) than thinner (20-30&nbsp;μm) hair (7.6&nbsp;mm per month).<ref>{{cite journal| author=Van Neste DJ, Rushton DH| title=Gender differences in scalp hair growth rates are maintained but reduced in pattern hair loss compared to controls. | journal=Skin Res Technol | year= 2016 | volume= 22 | issue= 3 | pages= 363–9 | pmid=26526232 | doi=10.1111/srt.12274 | pmc= | s2cid=19060270 }}</ref><ref>{{Cite journal|last1=Buffoli|first1=Barbara|last2=Rinaldi|first2=Fabio|last3=Labanca|first3=Mauro|last4=Sorbellini|first4=Elisabetta|last5=Trink|first5=Anna|last6=Guanziroli|first6=Elena|last7=Rezzani|first7=Rita|last8=Rodella|first8=Luigi F.|date=2014|title=The human hair: from anatomy to physiology|url=http://doi.wiley.com/10.1111/ijd.12362|journal=International Journal of Dermatology|language=en|volume=53|issue=3|pages=331–341|doi=10.1111/ijd.12362|pmid=24372228|s2cid=1310059|url-access=subscription}}</ref>

It was previously thought that Caucasian hair grew more quickly than Asian hair and that the growth rate of women's hair was faster than that of men.<ref name=Harkey/> However, more recent research has shown that the growth rate of hair in men and women does not significantly differ<ref>{{cite news |title=How Fast Does Hair Grow? |author=Joseph Castro |date=January 27, 2014 |work=Live Science |url=https://www.livescience.com/42868-how-fast-does-hair-grow.html |access-date=July 3, 2020}}</ref> and that the hair of Chinese people grew more quickly than the hair of French Caucasians and West and Central Africans.<ref>{{cite journal |last1=Loussouarn |first1=Geneviève |last2=El Rawadi |first2=Charles |last3=Genain |first3=Gilles |date=2005 |title=Diversity of hair growth profiles |journal=International Journal of Dermatology |volume=44 |issue=s1 |pages=6–9 |doi=10.1111/j.1365-4632.2005.02800.x |pmid=16187948 |s2cid=39103960 |doi-access=free }}</ref> The quantity of hair hovers in a certain range depends on hair colour.<ref>{{cite news |title=How many hairs are on a human head in total and per square inch?|work=curlcentric.com |url=https://www.curlcentric.com/how-many-hairs-are-on-a-human-head/|access-date=April 18, 2022}}</ref><ref>{{cite news |title=Number of hairs on human head |work=harvard.edu |url=https://bionumbers.hms.harvard.edu/bionumber.aspx?id=101509 |access-date=April 18, 2022 |archive-url=https://web.archive.org/web/20211214171336/https://bionumbers.hms.harvard.edu/bionumber.aspx?id=101509 |archive-date=14 December 2021 |url-status=dead}}</ref> An average [[blonde]] person has 150,000 hairs, a [[Brown hair|brown-haired]] person has 110,000, a [[Black hair|black-haired]] person has 100,000, and a [[redhead]] has 90,000.<ref>{{cite news|title=How much hair does a human have on their head?|work=mevolife.com|url=https://mevolife.com/blog/health/healthy-hair|access-date=April 18, 2022|archive-date=7 March 2023|archive-url=https://web.archive.org/web/20230307165927/https://mevolife.com/blog/health/healthy-hair|url-status=dead}}</ref> Hair growth stops after a human's death. Visible growth of hair on the dead body happens only because of skin drying out due to water loss.<ref>{{cite news |title=Do your hair and fingernails grow after death?|work=bbc.com |url=https://www.bbc.com/future/article/20130526-do-your-nails-grow-after-death|access-date=April 18, 2022}}</ref><ref name=TCP>{{cite book |doi=10.1007/978-3-642-02202-9_146 |chapter=Hair Disorders and Alopecia |chapter-url={{Google books|FEf4EMjYSrgC|page=1489|plainurl=yes}} |editor1-first=Abdelaziz Y. |editor1-last=Elzouki |editor2-first=Harb A. |editor2-last=Harfi |editor3-first=Hisham M. |editor3-last=Nazer |editor4-first=F. Bruder |editor4-last=Stapleton |editor5-first=William |editor5-last=Oh |editor6-first=Richard J. |editor6-last=Whitley |title=Textbook of Clinical Pediatrics |pages=1489–508 |year=2012 |last1=Ruszczak |first1=Zbigniew |isbn=978-3-642-02201-2 }}</ref>

The world record for longest hair on a living person stands with Smita Srivastava of [[Uttar Pradesh|Uttar Pradesh, India]]. At 7 feet and 9 inches long, she broke a [[Guinness World Records|Guinness World Record]] in November 2023, having grown her hair for 32 years.<ref>{{Cite web |date=2023-11-30 |title=UP woman, 46, sets world record with 7 ft 9 in long hair |url=https://www.hindustantimes.com/trending/up-woman-46-sets-world-record-with-7-ft-9-in-long-hair-101701329539286.html |access-date=2023-11-30 |website=Hindustan Times |language=en}}</ref>

===Texture===
[[File:Natural Afro - hair type 4c- model Gwyneth Ellis.jpg|thumb|Hair type 4c]]
Hair exists in a variety of textures. Three main aspects of hair texture are the curl pattern, volume, and consistency. All mammalian hair is composed of [[keratin]], so the make-up of [[hair follicles]] is not the source of varying hair patterns. There are a range of theories pertaining to the curl patterns of hair. Scientists have come to believe that the shape of the [[hair shaft]] has an effect on the curliness of the individual's hair. A very round shaft allows for fewer [[disulfide bonds]] to be present in the hair strand. This means the bonds present are directly in line with one another, resulting in straight hair.<ref name="Davidson genomics">{{cite web|title=Curly Hair Gene|url=http://www.bio.davidson.edu/courses/genomics/2011/Piper/Background.html|access-date=28 January 2015|publisher=Bio.davidson.edu}}</ref>
[[File:Curlsbaby.jpg|thumb|Toddler with curly hair]]

The flatter the hair shaft becomes, the curlier hair gets, because the shape allows more [[cysteine]]s to become compacted together resulting in a bent shape that, with every additional disulfide bond, becomes curlier in form.<ref name="Davidson genomics"/> 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.<ref name="hairdressing.ac.uk 153">{{cite web |url=http://hairdressing.ac.uk/node/153 |title=Hair type, texture and density &#124; Hairdressing Training |publisher=Hairdressing.ac.uk |access-date=28 January 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150212010906/http://hairdressing.ac.uk/node/153 |archive-date=12 February 2015 }}</ref> Fine hair has the smallest circumference, coarse hair has the largest circumference, and medium hair is anywhere between the other two.<ref name="hairdressing.ac.uk 153"/> Coarse hair has a more open cuticle than thin or medium hair, causing it to be the most porous.<ref name="hairdressing.ac.uk 153"/>

===={{anchor|classification}}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 and 3b curls.

=====Andre Walker system=====
{{Main|Andre Walker Hair Typing System}}

The Andre Walker Hair Typing System is the most widely used system to classify hair. The system was created by [[Oprah Winfrey]]'s hairstylist, [[Andre Walker]]. According to this system there are four types of hair: straight, wavy, curly, and 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 [[frizz]]y 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".{{Citation needed|reason=This is suspect (or confusing) because the uppercase "S" has the same shape as the lowercase variety|date=September 2016}} 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.

{| class="wikitable" style="margin:0 auto 2.0em;"
|+ style="font-size:105%;padding-bottom:0.2em;"|Andre Walker hair types
|-
!colspan="3"| Type 1: Straight
|-
!style="width:3.0em;"| 1a
| Straight (Fine/Thin)&nbsp;
| Hair tends to be very soft, thin, shiny, oily, poor at holding curls, difficult to damage.
|-
! 1b
| Straight (Medium)
| Hair characterized by volume and body.
|-
! 1c
| Straight (Coarse)
| Hair tends to be bone-straight, coarse, difficult to curl.
|-
!colspan="3"| Type 2: Wavy
|-
! 2a
| Wavy (Fine/Thin)
| Hair has definite "S" pattern, can easily be straightened or curled, usually receptive to a variety of styles.
|-
! 2b
| Wavy (Medium)
| Can tend to be frizzy and a little resistant to styling.
|-
! 2c
| Wavy (Coarse)
| Fairly coarse, frizzy or very frizzy with thicker waves, often more resistant to styling.
|-
!colspan="3"| Type 3: Curly
|-
! 3a
| Curly (Loose)
| Presents a definite "S" pattern, tends to combine thickness, volume, and/or frizziness.
|-
! 3b
| Curly (Tight)
| Presents a definite "S" pattern, curls ranging from spirals to spiral-shaped corkscrews.
|-
!colspan="3"| Type 4: Kinky
|-
! 4a
| Kinky (Soft)
| Hair tends to be very wiry and fragile, tightly coiled and can feature curly patterning.
|-
! 4b
| Kinky (Wiry)
| As 4a but with less defined pattern of curls, looks more like a "Z" with sharp angles.
|-
|}

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

{| class="wikitable" style="margin:0 auto;"
|+ style="font-size:105%;padding-bottom:0.2em;"|FIA hair classification
|-

<!---------------------- Curliness ------------------------>

!colspan="3" style="font-size:110%;"|
Curliness
|-
|colspan="3" style="text-align:center;"| '''''Straight'''''
|-
!style="width:3.0em;"| 1a
|colspan="2"| Stick-straight.
|-
! 1b
|colspan="2"| Straight but with a slight body wave adding some volume.
|-
! 1c
|colspan="2"| Straight with body wave and one or two visible S-waves (e.g. at nape of neck or temples).
|-
|colspan="3" style="text-align:center;"| '''''Wavy'''''
|-
! 2a
|colspan="2"| Loose with stretched S-waves throughout.
|-
! 2b
|colspan="2"| Shorter with more distinct S-waves (resembling e.g. braided damp hair).
|-
! 2c
|colspan="2"| Distinct S-waves, some spiral curling.
|-
|colspan="3" style="text-align:center;"| '''''Curly'''''
|-
! 3a
|colspan="2"| Big, loose spiral curls.
|-
! 3b
|colspan="2"| Bouncy ringlets.
|-
! 3c
|colspan="2"| Tight corkscrews.
|-
|colspan="3" style="text-align:center;"| '''''Very''' ("Really") '''curly'''''
|-
! 4a
|colspan="2"| Tightly coiled S-curls.
|-
! 4b
|colspan="2"| Z-patterned (tightly coiled, sharply angled)
|-
! 4c
|colspan="2"| Mostly Z-patterned (tightly kinked, less definition)
|-

<!----------------------- Strands ------------------------->

!colspan="3" style="font-size:110%;"|
Strands

|- style="vertical-align:top;"
! F
|colspan="2"| Fine

Thin strands that sometimes are almost translucent when held up to the light. <br />Shed strands can be hard to see even against a contrasting background. <br />Fine hair is difficult to feel or it feels like an ultra-fine strand of silk.

|- style="vertical-align:top;"
! M
|colspan="2"| Medium

Strands are neither fine nor coarse. <br />Medium hair feels like a cotton thread, but is not stiff or rough. <br />It is neither fine nor coarse.

|- style="vertical-align:top;"
! C
|colspan="2"| Coarse

Thick strands whose shed strands usually are easily identified. <br />Coarse hair feels hard and wiry.

|-

<!----------------------- Volume -------------------------->

!colspan="3" style="font-size:110%;"|Volume<br />{{small|{{nobold|by circumference of full-hair ponytail}}}}
|-
! i
| Thin || Circumference less than {{convert|2|in|cm|abbr=off}}
|-
! ii
| Normal || ...&nbsp;from {{convert|2|to|4|in|cm|abbr=off}}
|-
! iii
| Thick || ...&nbsp;more than {{convert|4|in|cm|abbr=off}}
|}

== Composition ==
Hair is mainly composed of [[keratin]] proteins and [[keratin-associated protein]]s (KRTAPs). The [[human genome]] encodes 54 different keratin proteins which are present in various amounts in hair. Similarly, humans encode more than 100 different KRTAPs which crosslink keratins in hair. The content of KRTAPs ranges from less than 3% in human hair to 30–40% in [[echidna]] quill.<ref>{{Citation |last1=Wu |first1=Dong-Dong |title=Evolution of Trichocyte Keratin Associated Proteins |date=2018 |url=https://doi.org/10.1007/978-981-10-8195-8_5 |work=The Hair Fibre: Proteins, Structure and Development |pages=47–56 |editor-last=Plowman |editor-first=Jeffrey E. |access-date=2023-03-04 |place=Singapore |publisher=Springer |language=en |doi=10.1007/978-981-10-8195-8_5 |isbn=978-981-10-8195-8 |last2=Irwin |first2=David M. |series=Advances in Experimental Medicine and Biology |volume=1054 |pmid=29797267 |editor2-last=Harland |editor2-first=Duane P. |editor3-last=Deb-Choudhury |editor3-first=Santanu|url-access=subscription }}</ref>

==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===
[[File:Ursus maritimus Steve Amstrup.jpg|thumb|left|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 [[Thermal insulation|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 (zoology)|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.<ref name="Why Do Humans Get goosebumps When They Are Cold, or under Other Circumstances?: Scientific American.">{{Cite journal|last=Bubenik|first=George A.|date=1 September 2003|title=Why do humans get "goosebumps" when they are cold, or under other circumstances?|url=http://www.scientificamerican.com/article.cfm?id=why-do-humans-get-goosebu|journal=Scientific American|access-date=4 May 2010}}</ref> 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 [[hedgehog]]s and [[porcupine]]s, 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]].<ref>{{Cite journal | doi = 10.1098/rsbl.2011.0987| pmid = 22171023| title = Human fine body hair enhances ectoparasite detection| journal = Biology Letters| volume = 8| issue = 3| pages = 358–61| year = 2011| last1 = Dean | first1 = I.| last2 = Siva-Jothy | first2 = M. T. | pmc=3367735}}</ref> Some hairs, such as [[eyelash]]es, are especially sensitive to the presence of potentially harmful matter.<ref>{{cite web|title=Neuroscience for Kids – Receptors|url=http://faculty.washington.edu/chudler/receptor.html|access-date=18 February 2015|publisher=Faculty.washington.edu}}</ref><ref>{{cite web|title=hair biology – functions of the hair fiber and hair follicle|url=http://www.keratin.com/aa/aa031.shtml|access-date=18 February 2015|publisher=Keratin.com|archive-date=30 March 2017|archive-url=https://web.archive.org/web/20170330014433/http://www.keratin.com/aa/aa031.shtml|url-status=dead}}</ref><ref>{{cite journal|pmid=4811387|last1=Sabah|first1=NH|year=1974|pages=256–7|issue=2|volume=36|title=Controlled stimulation of hair follicle receptors|journal=Journal of Applied Physiology|doi=10.1152/jappl.1974.36.2.256}}</ref><ref>{{Cite journal | doi = 10.1016/S0047-2484(85)80090-7| title = The evolution of human skin(?)| journal = Journal of Human Evolution| volume = 14| pages = 3–22| year = 1985| last1 = Montagna | first1 = W.| issue = 1| bibcode = 1985JHumE..14....3M}}</ref>
[[File:Jeremy Cadot's eyebrow.jpg|thumb|Eyebrows prevent sweat, water, and other debris from above from falling down into the eye.]]
[[File:Closed human eye, superior view.jpg|thumb|Eyelashes are hairs on the edges of the eyelids that catch dust and dirt when the eye is blinked.]]

====Eyebrows and eyelashes====
{{main|Eyebrows|Eyelashes}}

The [[eyebrow]]s provide moderate protection to the [[eye]]s 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 [[cat]]s; they are used to sense when dirt, [[dust]], or any other potentially harmful object is too close to the eye.<ref name="Thumbprints - The Human Eyelash.">{{cite web |url=http://ion.asu.edu/liv41_eyelash/liv41_thumb.htm |title=Images of Nature |publisher=Ion.asu.edu |access-date=18 February 2015 |url-status=dead |archive-url=https://web.archive.org/web/20060508183602/http://ion.asu.edu/liv41_eyelash/liv41_thumb.htm |archive-date=8 May 2006 }}</ref> The eye reflexively closes as a result of this [[sensation (psychology)|sensation]].

Eyebrows and eyelashes do not grow beyond a certain length (eyelashes are rarely more than 10&nbsp;mm long). However, [[trichomegaly]] can cause the lashes to grow remarkably long and prominent (in some cases the upper lashes grow to 15&nbsp;mm long).

==Evolution==
Hair has its origins in the common ancestor of mammals, the [[synapsid]]s, about 300 million years ago. It is currently unknown at what stage the synapsids acquired mammalian characteristics such as [[body hair]] and [[mammary gland]]s, as the [[fossil]]s 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 [[scute]]s, similar to those of a modern [[crocodile]], so the age of acquirement of hair logically could not have been earlier than ≈299 ma, based on the current understanding of the animal's phylogeny.<ref>{{cite journal|last1=Niedźwiedzki|first1=Grzegorz|last2=Bojanowski|first2=Maciej|title=A Supposed Eupelycosaur Body Impression from the Early Permian of the Intra-Sudetic Basin, Poland|journal=Ichnos|date=July 2012|volume=19|issue=3|pages=150–155|doi=10.1080/10420940.2012.702549|bibcode=2012Ichno..19..150N |s2cid=129567176}}</ref> An exceptionally well-preserved skull of ''[[Estemmenosuchus]]'', a [[therapsid]] from the [[Upper Permian]], shows smooth, hairless skin with what appears to be glandular depressions,<ref>Kardong, K.V. (2002): ''Vertebrates: Comparative anatomy, function, evolution. 3rd Edition.'' McGraw-Hill, New York</ref> 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 [[haramiyida]]ns, both [[Mammaliformes|near-mammal]] [[cynodont]]s, giving the age as no later than ≈220 ma based on the modern phylogenetic understanding of these clades.<ref name="JiLuoYuanTabrumCastorocauda">{{Cite journal|author1=Q. Ji|author2=Z-X Luo|author3=C-X Yuan|last4=Tabrum|first4=A. R.|date=February 2006|title=A Swimming Mammaliaform from the Middle Jurassic and Ecomorphological Diversification of Early Mammals|journal=Science|volume=311|issue=5764|pages=1123–7|bibcode=2006Sci...311.1123J|doi=10.1126/science.1123026|pmid=16497926|s2cid=46067702|url=http://doc.rero.ch/record/13437/files/PAL_E249.pdf }} See also the news item at {{cite web|title=Jurassic "Beaver" Found; Rewrites History of Mammals|url=http://news.nationalgeographic.com/news/2006/02/0223_060223_beaver.html|url-status=dead|archive-url=https://web.archive.org/web/20120922055901/http://news.nationalgeographic.com/news/2006/02/0223_060223_beaver.html|archive-date=22 September 2012|access-date=12 August 2012}}</ref><ref>{{cite news|date=9 August 2013|title=Jurassic squirrel's secret is out|newspaper=The Hindu|url=http://www.thehindu.com/opinion/op-ed/jurassic-squirrels-secret-is-out/article5004252.ece|access-date=29 June 2016}}</ref><ref>{{cite journal | last1 = Meng | first1 = Qing-Jin | last2 = Grossnickle | first2 = David M. | last3 = Di | first3 = Liu | last4 = Zhang | first4 = Yu-Guang | last5 = Neander | first5 = April I. | last6 = Ji | first6 = Qiang | last7 = Luo | first7 = Zhe-Xi | year = 2017 | title = New gliding mammaliaforms from the Jurassic | journal = Nature | volume = 548 | issue = 7667 | pages = 291–296 | doi = 10.1038/nature23476 | pmid = 28792929 | bibcode = 2017Natur.548..291M | s2cid = 205259206 }}</ref> More recently, studies on terminal [[Permian]] [[Russia]]n [[coprolites]] may suggest that non-mammalian synapsids from that era had fur.<ref>{{cite journal | doi = 10.1111/let.12156 | title=Microbiota and food residues including possible evidence of pre-mammalian hair in Upper Permian coprolites from Russia | year=2015 | journal=Lethaia | volume=49 | issue=4 | pages=455–477 | last1 = Bajdek | first1 = Piotr}}</ref> 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 (anatomy)|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]]''.<ref>{{cite book|last1=Lingham-Soliar|first1=Theagarten|title=The vertebrate integument, Vol I|date=2014|publisher=Springer Berlin Heidelberg|location=Berlin, Heidelberg|isbn=978-3-642-53748-6|pages=211–212}}</ref>

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 section of the brain that expanded markedly in animals like ''Morganucodon'' and ''[[Hadrocodium]]''.<ref>{{cite journal|last1=Rowe|first1=T. B.|last2=Macrini|first2=T. E.|last3=Luo|first3=Z.-X.|title=Fossil Evidence on Origin of the Mammalian Brain|journal=Science|date=19 May 2011|volume=332|issue=6032|pages=955–957|doi=10.1126/science.1203117|pmid=21596988|bibcode=2011Sci...332..955R|s2cid=940501}}</ref> The more advanced therapsids could have had a combination of naked skin, [[whisker]]s, and [[scute]]s. A full [[pelage]] likely did not evolve until the therapsid-mammal transition.<ref name=Fur>{{cite journal| last1=Ruben|first1= J.A. |last2= Jones| first2= T.D. |year=2000|title= Selective Factors Associated with the Origin of Fur and Feathers |journal=Am. Zool.|volume= 40|pages= 585–596 | doi = 10.1093/icb/40.4.585| issue=4 |doi-access= free}}</ref> 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]].<ref>{{cite book|last=Plower|first=R.P.|url=https://archive.org/stream/cu31924001022684/cu31924001022684_djvu.txt|title=An introduction to the study of mammals living and extinct|publisher=Cornell University Library|year=1897|location=New York|page=11|quote=Flat scutes, with the edges in apposition, and not overlaid, clothe both surfaces of the tail of the beaver, rats, and others of the same order, and also of some insectivores and marsupials.|access-date=8 June 2012}}</ref>

The high interspecific variability of the size, color, and microstructure of hair often enables the identification of species based on single hair filaments.<ref name=Teerink2003>{{cite book|author=Teerink, BJ|title=Hair of West European Mammals: Atlas and Identification Key |url= https://books.google.com/books?id=exlhpOZ__BEC| date=2003|publisher=Cambridge University Press| isbn=9780521545778| pages=224}}</ref><ref name="TothM">{{cite book|author=Toth, Maria|url=http://www.hairatlas.hu/|title=Hair and fur atlas of Central European mammals|date=29 December 2017|publisher=Pars Ltd|isbn=978-963-88339-7-6|pages=307|access-date=8 July 2019}}</ref>

[[File:Nacktmull.jpg|thumb|[[Naked mole-rat]] (''Heterocephalus glaber'') in a zoo.]]

{{anchor|Glabrous|Glabrousness}}

In varying degrees most [[mammal]]s have some skin areas without natural hair. On the human body, glabrous [[human skin|skin]] is found on the [[ventral]] portion of the [[finger]]s, [[hand|palms]], [[sole (foot)|soles of feet]] and [[lips]], which are all parts of the body most closely associated with interacting with the world around us,<ref name ="Scholarpedia">{{Cite book|title=Scholarpedia of touch|isbn=978-94-6239-133-8|location=Paris|oclc=932171320|last1=Prescott|first1=Tony|last2=Ahissar|first2=Ehud|last3=Izhikevich|first3=Eugene|date=21 November 2015}}</ref> as are the [[labia minora]] and [[glans penis]].<ref>{{cite book|last1=Linden|first1=David, J.|title=Touch: The Science of Hand, Heart and Mind|date=March 2015|publisher=Viking|isbn=978-0241184035|chapter-url=https://books.google.com/books?id=XjZIBQAAQBAJ&pg=PT36|chapter=Chapter 2}}</ref> There are four main types of [[mechanoreceptor]]s in the glabrous skin of humans: [[lamellar corpuscle|Pacinian corpuscles]], [[tactile corpuscle|Meissner's corpuscles]], [[Merkel nerve ending|Merkel's discs]], and [[bulbous corpuscle|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.<ref name ="Scholarpedia"/> Glabrousness is a trait that may be associated with [[neoteny]].<ref>{{Cite journal|last=Rebora|first=Alfredo|date=2010|title=Lucy's pelt: when we became hairless and how we managed to survive|journal=International Journal of Dermatology|language=en|volume=49|issue=1|pages=17–20|doi=10.1111/j.1365-4632.2009.04266.x|pmid=20465604|s2cid=21484729|issn=1365-4632}}</ref>

[[file:Vulpes vulpes sitting.jpg|thumb|The soft, fine hair found on many nonhuman mammals is typically called fur.<!-- moved ref to main text, above: name=Bergman2014 -->]]

===Evolutionary variation===
Primates are relatively hairless compared to other mammals, and [[Hominini]] such as chimpanzees, have less dense hair than would be expected given their body size for a primate.<ref name="Sandel 2013 pp. 145–150">{{cite journal |last=Sandel |first=Aaron A. |date=2013-07-30 |title=Brief communication: Hair density and body mass in mammals and the evolution of human hairlessness |journal=American Journal of Physical Anthropology |volume=152 |issue=1 |pages=145–150 |doi=10.1002/ajpa.22333 |pmid=23900811 |issn=0002-9483|hdl=2027.42/99654 |hdl-access=free }}</ref> Evolutionary biologists suggest that the genus ''[[Homo]]'' arose in [[East Africa]] approximately 2 million years ago.<ref name="Herries Martin Leece Adams 2020 p.">{{cite journal |last1=Herries |first1=Andy I. R. |last2=Martin |first2=Jesse M. |last3=Leece |first3=A. B. |last4=Adams |first4=Justin W. |last5=Boschian |first5=Giovanni |last6=Joannes-Boyau |first6=Renaud |last7=Edwards |first7=Tara R. |last8=Mallett |first8=Tom |last9=Massey |first9=Jason |last10=Murszewski |first10=Ashleigh |last11=Neubauer |first11=Simon |last12=Pickering |first12=Robyn |last13=Strait |first13=David S. |last14=Armstrong |first14=Brian J. |last15=Baker |first15=Stephanie |date=2020-04-03 |title=Contemporaneity of ''Australopithecus'', ''Paranthropus'', and early ''Homo erectus'' in South Africa |journal=Science |volume=368 |issue=6486 |page= |doi=10.1126/science.aaw7293 |issn=0036-8075 |last16=Caruana |first16=Matthew V. |last17=Denham |first17=Tim |last18=Hellstrom |first18=John |last19=Moggi-Cecchi |first19=Jacopo |last20=Mokobane |first20=Simon |last21=Penzo-Kajewski |first21=Paul |last22=Rovinsky |first22=Douglass S. |last23=Schwartz |first23=Gary T. |last24=Stammers |first24=Rhiannon C. |last25=Wilson |first25=Coen |last26=Woodhead |first26=Jon |last27=Menter |first27=Colin|pmid=32241925 |doi-access=free |hdl=11568/1040368 |hdl-access=free }}</ref> Part of this evolution was the development of [[Endurance running hypothesis|endurance running]]<ref name="Ruxton Wilkinson 2011 pp. 169–175">{{cite journal |last1=Ruxton |first1=Graeme D. |last2=Wilkinson |first2=David M. |year=2011 |title=Thermoregulation and endurance running in extinct hominins: Wheeler's models revisited |journal=Journal of Human Evolution |volume=61 |issue=2 |pages=169–175 |doi=10.1016/j.jhevol.2011.02.012 |pmid=21489604 |bibcode=2011JHumE..61..169R |issn=0047-2484}}</ref> and venturing out during the hot times of the day<ref name="Ruxton Wilkinson 2011 pp. 20965–20969">{{cite journal |last1=Ruxton |first1=Graeme D. |last2=Wilkinson |first2=David M. |date=2011-12-12 |title=Avoidance of overheating and selection for both hair loss and bipedality in hominins |journal=Proceedings of the National Academy of Sciences |volume=108 |issue=52 |pages=20965–20969 |doi=10.1073/pnas.1113915108 |pmid=22160694 |pmc=3248486 |bibcode=2011PNAS..10820965R |issn=0027-8424|doi-access=free }}</ref> that required efficient thermoregulation through [[perspiration]]. The loss of heat through [[heat of evaporation]] by means of [[sweat gland]]s is aided by air currents next to the skin surface, which are facilitated by the loss of body hair.<ref name="Jablonski06">{{cite book |author=Jablonski, Nina G. |url=https://books.google.com/books?id=EYi9S3VtIGsC&pg=PP13 |title=Skin: A Natural History |date=1 May 2008 |publisher=University of California Press |isbn=978-0-520-94170-0 |pages=13– |access-date=27 January 2016}}</ref>

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 other great apes, is about a century old. [[Louis Bolk]] made a long list of such traits,<ref>{{Cite book|last=Bolk|first=L.|year=1926|title=Das Problem der Menschwerdung|publisher=Fischer|location=Jena|language=de}}</ref> and [[Stephen Jay Gould]] published a short list in ''[[Ontogeny and Phylogeny (book)|Ontogeny and Phylogeny]]''.<ref>short-list of 25 characters reprinted in Gould, Stephen Jay (1977). ''[[Ontogeny and Phylogeny (book)|Ontogeny and phylogeny]]''. Harvard University Press. p. 357. {{ISBN|0674639413}}.</ref> In addition, [[paedomorphic]] characteristics in women are often [[Physical attractiveness#Determinants of female physical attractiveness|acknowledged as desirable by men]] in developed countries.<ref>{{cite journal |last1=Scott|first1= Isabel M.|date=7 October 2014 |title=Human preferences for sexually dimorphic faces may be evolutionarily novel |journal=Proceedings of the National Academy of Sciences of the United States of America|volume=111 |issue=40 |pages= 14388–14393|doi=10.1073/pnas.1409643111 |pmid= 25246593|pmc= 4210032|bibcode=2014PNAS..11114388S|doi-access= free}}</ref> 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.
{{further|Human evolutionary genetics}}

===Texture===

====<span id="curly"></span>Curly hair====
[[File: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.jpg|thumb|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]]
[[File:David Luiz ConfedCup2013Champions17.jpg|thumb|Man with curly hair ([[David Luiz]], Brazilian footballer)]]
[[File:PSM V52 D323 Global hair texture map.png|thumb|Global hair texture map]]
{{More citations needed section|date=August 2016}}
Jablonski<ref name=Jablonski06/> 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{{Citation needed|date=September 2010}} (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 findings {{citation needed|date=November 2024}}(1998) 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.

Jablonski's assertions<ref name=Jablonski06/> 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,<ref name=Jablonski06/> 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).

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.

[[File:Blackhair10.jpg|thumb|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]].<ref>{{cite journal|pmid=18065779|last1=Fujimoto|first1=A|year=2008|pages=835–43|issue=6|volume=17|last2=Kimura|first2=R|journal=Human Molecular Genetics|last3=Ohashi|first3=J|last4=Omi|first4=K|last5=Yuliwulandari|first5=R|last6=Batubara|first6=L|last7=Mustofa|first7=MS|last8=Samakkarn|first8=U|last9=Settheetham-Ishida|first9=W|last10=Ishida|first10=T.|last11=Morishita|first11=Y.|last12=Furusawa|first12=T.|last13=Nakazawa|first13=M.|last14=Ohtsuka|first14=R.|last15=Tokunaga|first15=K.|title=A scan for genetic determinants of human hair morphology: EDAR is associated with Asian hair thickness|doi=10.1093/hmg/ddm355|display-authors=8|doi-access=free}}</ref><ref>{{cite journal|pmid=18704500|last1=Fujimoto|first1=A|year=2008|pages=179–85|issue=2|volume=124|last2=Ohashi|first2=J|journal=Human Genetics|last3=Nishida|first3=N|last4=Miyagawa|first4=T|last5=Morishita|first5=Y|last6=Tsunoda|first6=T|last7=Kimura|first7=R|last8=Tokunaga|first8=K|title=A replication study confirmed the EDAR gene to be a major contributor to population differentiation regarding head hair thickness in Asia|url=http://www.tulips.tsukuba.ac.jp/dspace/bitstream/2241/103672/1/HG_124-2.pdf|doi=10.1007/s00439-008-0537-1|access-date=14 December 2010|archive-url=https://web.archive.org/web/20110205011119/http://www.tulips.tsukuba.ac.jp/dspace/bitstream/2241/103672/1/HG_124-2.pdf|archive-date=5 February 2011|url-status=dead|hdl=2241/103672|s2cid=20084816|hdl-access=free}}</ref><ref>{{cite journal|last1=Mou|first1=C|last2=Thomason|first2=HA|last3=Willan|first3=PM|last4=Clowes|first4=C|last5=Harris|first5=WE|last6=Drew|first6=CF|last7=Dixon|first7=J|last8=Dixon|first8=MJ|last9=Headon|first9=DJ|year=2008|title=Enhanced ectodysplasin-A receptor (EDAR) signaling alters multiple fiber characteristics to produce the East Asian hair form|url=https://www.pure.ed.ac.uk/ws/files/8264337/Mou_et_al_EDAR_and_Asian_Hair_2008_supplementary_material.pdf|journal=Human Mutation|volume=29|issue=12|pages=1405–11|doi=10.1002/humu.20795|pmid=18561327|hdl=20.500.11820/0b35a959-86c8-44e5-b100-20639dd6bbf1|s2cid=37696013|access-date=30 January 2019|hdl-access=free}}</ref> 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==
{{See also|Hair diseases}}
[[Tinea corporis|Ringworm]] is a [[mycosis|fungal disease]] that targets hairy skin.<ref>{{cite web|title=Dermatologyinfo.net|url=http://www.dermatologyinfo.net/english/chapters/chapter10.htm|access-date=21 May 2012|publisher=Dermatologyinfo.net}}</ref>

[[Premature greying of hair]] is another condition that results in greying before the age of 20 years in Europeans, before 25 years in Asians, and before 30 years in Africans.<ref>{{Cite journal|title=Premature graying of hair|date = 31 August 2013| pmid=23974581 |url=http://www.ijdvl.com/article.asp?issn=0378-6323;year=2013;volume=79;issue=5;spage=641;epage=653;aulast=Pandhi#ref4|access-date=15 November 2017| last1=Pandhi | first1=D. | last2=Khanna | first2=D. | journal=Indian Journal of Dermatology, Venereology and Leprology | volume=79 | issue=5 | pages=641–653 | doi=10.4103/0378-6323.116733 | doi-access=free }}</ref>

== Hair care ==
{{Main|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====
{{Main|Shaving}}
[[File:Shaving-system-2blade.jpg|thumb|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 [[Shaving|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{{citation needed|date=November 2024}}.

====Laser removal====
{{main|Laser hair 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====
{{see also|Ponytail}}

Because the hair on one's head is normally longer than other types of body hair, it is cut with [[scissors]] or [[Manual hair clippers|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 [[wig]]s. Global imports of hair in 2010 was worth $US 1.24 billion.<ref>{{cite journal|last1=Gupta|first1=Ankush|title=Human Hair "Waste" and Its Utilization: Gaps and Possibilities|journal=Journal of Waste Management|date=27 April 2014|doi=10.1155/2014/498018 |doi-access=free|volume=2014|pages=1–17}}</ref>

==Social role==
{{See also|Hairstyle}}
[[File:Alessandro Allori - Portrait of Bianca Cappello.jpg|thumb|upright|''Portrait of a Woman'' by Alessandro Allori (1535–1607) at [[Uffizi Gallery]]. It shows a plucked hairline that gives a fashionably noble brow.]]
Hair has great social significance for [[human being]]s.<ref>{{cite journal|doi=10.11141/ia.42.6 | issue=42 | title=Archaeologies of Hair: the head and its grooming in ancient and contemporary societies | year=2016 | journal=Internet Archaeology | last1 = Ashby | first1 = Steven P.| doi-access=free }}</ref><ref>{{cite journal|doi=10.11141/ia.42.6.13 | issue=42 | title=Because You're Worth It: Women's daily hair care routines in contemporary Britain | year=2016 | journal=Internet Archaeology | last1 = Hielscher | first1 = Sabine | doi-access=free }}</ref> It can grow on most external areas of the [[human body]], except on the palms of the [[hand]]s 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, [[Plucking (hair removal)|plucked]], or [[shaving|shaved]]. These include the [[face]], [[ear]]s, [[human head|head]], eyebrows, [[human leg|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]].

The world's longest documented hair belongs to [[Xie Qiuping]] (in [[China]]), at {{convert|5.627|m|ftin|abbr=on}} when measured on 8 May 2004. She has been growing her hair since 1973, from the age of 13.<ref>{{Cite book|title=Guinness World Records 2011|last=Glenday|first=Craig|year=2010|publisher=Guinness World Records |isbn=9781904994572|url-access=registration|url=https://archive.org/details/guinnessworldrec00}}</ref>

===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 or gray hair is a sign of age or genetics, which may be concealed with [[Hair coloring|hair dye]] (not easily for some), although many prefer to assume it (especially if it is a [[poliosis]] characteristic of the person since childhood). [[Pattern baldness]] in men is usually seen as a sign of aging that may be concealed with a [[toupee]], hats, or religious and cultural adornments; however, the condition can be triggered by various hormonal factors at any age following puberty and is not uncommon in younger men. Although pattern baldness can be slowed down by drugs such as [[Finasteride]] and [[Minoxidil]] or treated with [[hair transplant]]s, many men see this as unnecessary effort for the sake of vanity and instead [[Head shaving|shave their heads]]. In early modern China, the [[Queue (hairstyle)|queue]] was a male hairstyle in which the hair at the front and top was shaved every 10 days in a style mimicking pattern baldness, while the remaining hair at the back was braided into a long pigtail.

A hairstyle may be an indicator of group membership. During the [[English Civil War]], followers of [[Oliver Cromwell]] cropped their hair close to their head in an act of defiance against the curls and ringlets of the king's men, which led to them being nicknamed [[Roundhead]]s.<ref>Olmert, Michael (1996). ''Milton's Teeth and Ovid's Umbrella: Curiouser & Curiouser Adventures in History'', p. 53. Simon & Schuster, New York. {{ISBN|0-684-80164-7}}</ref> 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.<ref>{{cite journal|doi=10.11141/ia.42.6.12 | issue=42 | title=Hair as a Window on Diet and Health in Post-Medieval London: an isotopic analysis | year=2016 | journal=Internet Archaeology | last1 = Brown | first1 = Chloe | last2 = Alexander | first2 = Michelle | doi-access=free }}</ref> Having [[Bob cut|bobbed hair]] was popular among the [[flapper]]s 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 of Fine Art|Slade School]] in [[London]]. Regional variations in [[hirsutism]] has caused 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 [[hippie]]s, [[Heavy metal subculture|metalheads]], and Indian [[sadhus]] have long hair, as well many older [[Hipster (contemporary subculture)|hipsters]]. Many [[punk fashion|punks]] wear a hairstyle known as a [[Mohawk hairstyle|mohawk]] or other spiked and dyed hairstyles, while [[skinhead]]s have short-cropped or completely shaved heads. Long stylized bangs were very common for [[Emo (stereotype)|emo]]s, [[Scene (subculture)|scene kids]], and younger hipsters in the 2000s and early 2010s.

Heads were shaved in [[concentration camp]]s, 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.<ref>{{Cite book |last=Berger |first=Arthur Asa |title=USA Pop |date=2020 |isbn=978-1-5275-5998-1 |location=Newcastle upon Tyne |oclc=1199967093}}</ref><ref>{{Cite book |last=Innes |first=William C. |title=Religious hair display and its meanings |date=2021 |isbn=978-3-030-69974-1 |location=Cham, Switzerland |oclc=1249505982}}</ref><ref>{{Cite book |title=Cultural History of Hair in the Modern Age. |date=2021 |publisher=Bloomsbury Academic |isbn=978-1-350-12283-3 |oclc=1223027644}}</ref><ref>{{Cite book |title=Hair : its power and meaning in Asian cultures |date=1998 |publisher=State University of New York Press |others=Alf Hiltebeitel, Barbara D. Miller |isbn=0-7914-3741-8 |location=Albany |oclc=37254408}}</ref>

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 American]]s 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 ([[Eurocentrism|eurocentric]]) dominant culture are not absolute. 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 England's 1971 [[Oz trial|''Oz'' trials]], the defendants had their heads shaved by the police, causing public outcry. During the appeal trial, they appeared in the dock wearing wigs.<ref>[[Jonathon Green|Green, Jonathon]], (1999). ''All Dressed Up: The Sixties and the Counterculture''. London: Pimlico. {{ISBN|0-7126-6523-4}}.</ref> 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.<ref name="cearamohawk1">{{cite web|date=28 September 2011|title=G1 – Justiça do CE condena escola por barrar aluno com cabelo 'moicano' – notícias em Ceará|trans-title=G1 - CE court condemns school for barring student with 'mohawk' hair - news in Ceara|url=http://g1.globo.com/ceara/noticia/2011/09/justica-do-ce-condena-escola-por-barrar-aluno-com-cabelo-moicano.html|access-date=18 February 2015|publisher=G1.globo.com}}</ref><ref name="cearamohawk2">{{cite web|date=30 September 2011|title=G1 – Aluno diz que jogador inspirou 'corte moicano' alvo de ação judicial no CE – notícias em Ceará|trans-title=G1 says student inspired 'Mohawk court' subject to legal action in CE - news in Ceara|url=http://g1.globo.com/ceara/noticia/2011/09/aluno-diz-que-jogador-inspirou-corte-moicano-alvo-de-acao-judicial-no-ce.html|access-date=18 February 2015|publisher=G1.globo.com}}</ref>

===Religious practices===
Women's hair may be hidden using [[headscarf|headscarves]], a common part of the ''[[hijab]]'' in [[Islam]] and a symbol of modesty required for certain religious rituals in [[Eastern Orthodox Church|Eastern Orthodoxy]]. The [[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. [[Sikhism|Sikhs]] have an obligation not to cut hair (a Sikh cutting hair becomes 'apostate' which means fallen from religion)<ref>Dilgeer, Harjinder Singh (2005) ''Dictionary of Sikh Philosophy'', Sikh University Press.</ref> 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]] [[madhab]]s, the donning of a [[kufi]] or [[Taqiyah (cap)|topi]] is a form of [[sunnah]].<ref>The War Within Our Hearts – Page 65 Sa'ad Quadri – 2013</ref> [[Brahmin]] males are prescribed to shave their heads, but leave a tuft of hair unshaved, worn in the form of a topknot.<ref>{{Cite book |last1=Hiltebeitel |first1=Alf |url=https://books.google.com/books?id=PRPymT12c40C&dq=Brahmin+male+topknot&pg=PA15 |title=Hair: Its Power and Meaning in Asian Cultures |last2=Miller |first2=Barbara D. |last3=Miller |first3=Professor of Anthropology and Director of the Women's Studies Program Barbara D. |date=1998-01-01 |publisher=SUNY Press |isbn=978-0-7914-3741-4 |pages=15 |language=en}}</ref>

===In Arabic poetry===
Since ancient times, women's long, thick, wavy hair has featured prominently in [[Arabic poetry]].<ref name="Sha'r">{{cite book |last1=Sadan|first1=J. |last2=Reinhart |first2=A.K. |last3=Reinert |first3=B. |editor1-last=Bosworth |editor1-first=C.E. |editor2-last=van Donzel |editor2-first=E. |editor3-last=Heinrichs |editor3-first=W.P. |editor4-last=Lecomte |editor4-first=G. |title=The Encyclopaedia of Islam, Vol. IX (SAN-SZE) |date=1997 |publisher=Brill |location=Leiden |isbn=90-04-10422-4 |pages=311–3 |url=https://ia600603.us.archive.org/14/items/EncyclopaediaDictionaryIslamMuslimWorldEtcGibbKramerScholars.13/09.EncycIslam.NewEdPrepNumLeadOrient.EdEdComCon.BosDonHeinLec.etc.UndPatIUA.v9.San-Sze.Leid.EJBrill.1997..pdf |access-date=13 June 2022 |chapter=SHA'R}}</ref> Pre-Islamic poets used only limited imagery to describe women's hair.<ref name="Sha'r"/> For example, [[al-A'sha]] wrote a verse comparing a lover's hair to "a garden whose grapes dangle down upon me", but [[Bashshar ibn Burd]] considered this unusual.<ref name="Sha'r"/> One comparison used by early poets, such as [[Imru al-Qays]], was to bunches of [[date (fruit)|date]]s.<ref name="Sha'r"/> In [[Abbasid]] times, however, the imagery for hair expanded significantly - particularly for the then-fashionable "love-locks" (''sudgh'') framing the [[temple (anatomy)|temple]]s, which came into style at the court of the caliph [[al-Amin]].<ref name="Sha'r"/> Hair curls were compared to hooks and chains, letters (such as ''[[fa (letter)|fa]]'', ''[[waw (letter)|waw]]'', ''[[lam (letter)|lam]]'', and ''[[nun (letter)|nun]]''), [[scorpion]]s, [[annelid]]s, and [[polo stick]]s.<ref name="Sha'r"/> An example was the poet [[Ibn al-Mu'tazz]], who compared a lock of hair and a [[birthmark]] to a polo stick driving a ball.<ref name="Sha'r"/>

==See also==
{{div col}}
* [[Body hair]]
* [[Bristle sensilla]] – tactile hairs in insects
* [[Chaetophobia]] – the fear of hair
* [[Hair analysis (alternative medicine)]]
* [[Hypertrichosis]] – the state of having an excess of hair on the head or body
* [[Hypotrichosis]] – the state of having a less than normal amount of hair on the head or body
* [[Lanugo]]
* [[List of hairstyles]]
* [[Mane (horse)]]
* [[Prehistory of nakedness and clothing#Evolution of hairlessness|Prehistory of nakedness and clothing]] - how humans lost most of their body hair
* [[Seta]] – hair-like structures in insects
* [[Trichotillomania]] – hair pulling
{{div col end}}

==References==

===Citations===
{{reflist|25em}}

===Sources===
* {{cite journal |ref=Iyengar1998 |last=Iyengar |first=B. |year=1998 |title=The hair follicle is a specialized UV receptor in human skin? |journal=Bio Signals Recep |volume=7 |issue=3 |pages=188–194 |doi=10.1159/000014544 |pmid=9672761 |s2cid=46864921 }}
* {{cite book |ref=Jablonski2006 |last=Jablonski |first=N.G. |year=2006 |title=Skin: a natural history |url=https://archive.org/details/skinnaturalhisto00jabl |url-access=registration |location=Berkeley, CA |publisher=University of California Press}}
* {{cite journal |ref=Rogers2004 |last1=Rogers |first1=Alan R. |last2=Iltis |first2=David |last3=Wooding |first3=Stephen |year=2004 |title=Genetic variation at the MC1R locus and the time since loss of human body hair |journal=Current Anthropology |volume=45 |issue=1 |pages=105–108 |doi=10.1086/381006 |s2cid=224795768 }}
* {{cite journal |ref=Tishkoff1996 |last1=Tishkoff |first1=S. A. |year=1996 |title=Global patterns of linkage disequilibrium at the CD4 locus and modern human origins |journal=Science |volume=271 |issue=5254 |pages=1380–1387 |bibcode=1996Sci...271.1380T |last2=Dietzsch |first2=E. |last3=Speed |first3=W. |last4=Pakstis |first4=A. J. |last5=Kidd |first5=J. R. |last6=Cheung |first6=K. |last7=Bonne-Tamir |first7=B. |last8=Santachiara-Benerecetti |first8=A. S. |last9=Moral |first9=P. |last10=Krings |first10=M. |last11=Paabo |first11=S. |last12=Watson |first12=E. |last13=Risch |first13=N. |last14=Jenkins |first14=T. |last15=Kidd |first15=K. K. |doi=10.1126/science.271.5254.1380 |pmid=8596909 |s2cid=4266475 |display-authors=8 }}

==External links==
{{Commons category}}
{{Wikiquote}}
{{Wiktionary}}
* [https://web.archive.org/web/20090628170110/http://www.fysikbasen.dk/English.php?page=HairMeasure How to measure the diameter of your own hair using a laser pointer]
* [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]]
* {{Cite news |url=https://www.zmescience.com/other/science-abc/how-fast-hair-grows-042394 |title=How fast hair grows, and other hairy science |last=PUIU |first=TIBI |date=23 August 2018 |work=ZME Science |access-date=30 August 2018 |language=en-US}}

{{Integumentary system}}
{{Human Evolution}}
{{Human hair}}
{{Human regional anatomy}}
{{Authority control}}

[[Category:Hair| ]]
[[Category:Human hair| ]]