Editing Hair (section)

== 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#Hair-follicle cycling|anagen]], [[Hair follicle#Hair-follicle cycling|catagen]], and [[Hair follicle#Hair-follicle cycling|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 | url=https://pubmed.ncbi.nlm.nih.gov/26526232  }}</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}}</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 depending 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 2 inches (5 centimetres)
|-
! ii
| Normal || ...&nbsp;from 2 to 4 inches (5 to 10 centimetres)
|-
! iii
| Thick || ...&nbsp;more than 4 inches (10 centimetres)
|}