Human hair color
Hair color is the result of pigmentation due to the presence of the chemicals of melanin and phaeomelanin.
Human beings have many variations in hair color and hair texture. In general, the more melanin, the darker the hair color; less melanin, the lighter the hair color. Usually the color of children's and adults' hair varies from pale yellow (blonde) to deep black. Hair may also come in more than one shade of color on one's head. As an example, the shade of one's hair color may change from a light shade to a darker one as time elapses.
The ethnic distribution of colors has historically varied by geographic area. For example, black hair predominates outside of Europe. All possible shades from black to brown to blonde to red occur in Europeans and their descendants.
Considerable differences in hair color and texture exist between individuals of similar ethnicity, and immigration and global travel have greatly increased the diversity of hair characteristics in many countries. People also dye their hair to colors that do not occur naturally.
Pigment
There are two types of pigment that gives hair its color, eumelanin and phaeomelanin. Eumelanin is black, and pheomelanin is red. All humans have pheomelanin in their hair. How dark it is depends on how much eumelanin is present. A low concentration of eumelanin in the hair will give blonde hair, more eumelanin will give it a brown color, and much higher amounts of eumelanin will result in black hair. Eumelanin in low concentrations causes a yellow tone, in higher concentrations creates a brown color.
Pheomelanin is more chemically stable than eumelanin, so it breaks down more slowly when oxidized. It is for this reason that Egyptian mummies have reddish hair, as the pheomelanin is still present but the eumelanin has broken down. This is also the reason bleach will cause darker hair to turn red as it is processing, when it has broken down the eumelanin quickly but acts more slowly on the pheomelanin. As the pheomelanin breaks down, the hair will then become orange, then the chemicals turn it yellow.
Effects of aging on hair color
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A change in hair color typically occurs naturally as people age, usually turning their hair from its natural color to grey, then to white. More than 40 percent of Americans have some grey hair by their fortieth birthday, but grey hairs can appear as early as the teens and twenties for some, or even in childhood. The determination of when someone begins greying, whether it comes with aging or prematurely, seems to be almost entirely based on genetics. Sometimes people are born with grey hair because it is passed down genetically. Many people use hair dye to disguise the amount of grey in their hair.
The change in hair color is caused by the gradual decrease of pigmentation that occurs when melanin ceases to be produced in the hair root, and new hairs grow in without pigment. Two genes appear to be responsible for the process of greying, Bcl2 and Mitf. The stem cells at the base of hair follicles are responsible for producing melanocytes, the cells that produce and store pigment in hair and skin. The death of the melanocyte stem cells causes hair to begin going grey.[1]
There are no special diets, nutritional supplements, vitamins, nor proteins that have been proven to slow, stop, or in any way affect the greying process, although many have been marketed over the years. This may change in the near future, however. French scientists treating leukemia patients with a new cancer drug noted an unexpected side effect: some of the patients' pre-grey hair color had been restored. [1]
A 1996 British Medical Journal study conducted by J.G. Mosley, MD found that tobacco smoking may cause premature greying. Smokers were found to be four times more likely to begin greying prematurely, compared to nonsmokers in the study.[2]
The colour of the hair of mummies or buried people can change over large time periods. Hair contains a mixture of black-brown-yellow eumelanin and red phaeomelanin. Phaeomelanin is much more stable than eumelanin, so that the phaeomelanin in the hair is better preserved over time than the eumelanin. The colour of hair changes faster under extreme conditions. It changes more slowly under dry oxidising conditions (such as in burials in sand or in ice) than under wet reducing conditions (such as burials in wood or plaster coffins).[3]
Medical conditions affecting hair color
Albinism is a genetic abnormality where no pigment is found in human hair, eyes or skin, making the eyes grey, blue, or red and the hair pale white or blonde, and the skin pale white.
Vitiligo is a patchy loss of hair and skin colour that may occur as the result of an auto-immune disease.
Malnutrition is also known to cause hair to become lighter, thinner, and brittler. Dark hair may thus turn reddish or blondish due to the decreased production of melanin. The condition is reversible with proper nutrition.
Werner syndrome and pernicious anaemia can also cause premature greying. A recent study demonstrated that people 50-70 years of age with dark eyebrows but grey hair are significantly more likely to have type II diabetes than those with both grey eyebrows and grey hair.[4]
Grey hair may temporarily darken after inflammatory processes, after electron-beam-induced alopecia, and after some chemotherapy regimens. Much remains to be learned about the physiology of human greying.[5]
Genetics
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At least two gene pairs control human hair color. One gene, which is a brown/blonde pair, has a dominant brown allele and a recessive blonde allele. If a person carries the brown allele, they will have brown hair; otherwise, they will be blonde. This also explains why two brown-haired parents can produce a blonde-haired child. The other gene pair is a not-red/red pair, where the not-red allele (which suppresses production of phaeomelanin) is dominant and the allele for red hair is recessive. Since the two gene pairs both govern hair color, a person with two copies of the red-haired allele will have red hair, but it will be either auburn or bright reddish orange depending upon whether the first gene pair gives a brown or blonde hair color respectively. The recessive genes for both brown/blonde and red hair are found nearly exclusively in populations of white people. There is also a black gene, usually related to darker skinned humans.
However, the two-gene model cannot explain the various shades of brown, blonde, or red which may occur (for example, platinum blonde versus dark blonde/light brown), or why one blonde child's hair might turn brown as he grows up while another blonde child's hair does not. According to some research,[weasel words] there are several gene pairs that control the light versus dark hair color in an accumulative effect. Therefore, the more of these that are dominant, the darker the hair will be.
The light hair distribution map shown here refers to light hair as being blonde, brown, and red. And dark as being black.
Common hair colors
Natural hair color is generally blond, red, brown, or black depending on the ethnic origins of the person in question. Hair color is genetically associated with certain skin tones, eye colors, and disorders such as skin cancer or albinism in persons with blond or red hair. Black hair is the most common.[6]
Black hair
Black hair is found in people of non-European heritage most commonly, but occurs in people of all backgrounds and ethnicities. It has large amounts of eumelanin and is less dense than other hair colors. It can be almost completely black or very deep black with different hair texture depending on the person and the ethnicity. For example most people of East Asian descent have straight black hair, while people of sub-Saharan African descent generally have thick, coarse hair. The many black-haired Caucasoids of the Mediterranean, Middle East, North Africa, South Asia, and the British Isles exhibit practically all hair forms but woolly.
Brown hair
Brown hair is also found all over the world. Brown and blonde hair are based on the same gene. It is very common that people with brown hair were born blondes, and over time turns brown. It has more eumelanin than blond hair but also has much less than black. Brown-haired people have medium-thick strands of hair. A brown-haired male is a brunet; a female is a brunette.
Blond hair
Blond hair is a relatively rare human phenotype, occurring in approximately 2% of the world population with the majority of natural blondes being white.
Blond hair ranges from nearly white (platinum blond, tow-haired) to a dark golden blonde. Strawberry blond is a rare type: a mixture of blond and red hair. Blondness is a recessive gene. Blond hair can have almost any proportions of phaeomelanin and eumelanin, but both only in small amounts. More phaeomelanin creates a more golden blonde color, and more eumelanin creates a "dishwater" or ash blonde. Natural blondes have the thinnest strand of hair. Blond hair is common in Sweden, Finland, Iceland, Norway, Denmark, Germany, Netherlands, England, Scotland and the Baltic States. It also occurs in some Melanesian and Australian Aborigine populations.
Red hair
Red hair is the least common hair color. It ranges from vivid strawberry shades to deep auburn and burgundy, and is found mainly in people of Northern, specifically those residing in the British Isles, and less commonly, of Scandinavian descent.
Red hair is caused by a mutation of the Mc1r gene and is believed to be recessive.[7] Red hair has the highest amounts of phaeomelanin and usually low levels of eumelanin. Natural redheads have the thickest strands of hair.
Hair color names
Names for human hair colors include:
- brown, brunette, mahogany, chocolate, cinnamon, dark, chestnut
- jet black, raven, midnight, raveonette, dark, sable, ebony, onyx, black, domino
- flaxen, fair, tow-headed, blonde, sandy blonde, dirty blonde, dishwater blonde, strawberry blonde, honey, golden, platinum blonde
- auburn, chestnut, red, fiery, redhead, titian, russet, ginger, scarlet, cinnamon
- silver, salt and pepper, white, grey, alabaster, snow, platinum and Arctic blond
See also
Footnotes
- ^ Nishimura EK, Granter SR, Fisher DE (2005). "Mechanisms of hair greying: Incomplete melanocyte stem cell maintenance in the niche". Science. 307 (5710): 720–4. PMID 15618488.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ http://bmj.bmjjournals.com/cgi/content/full/313/7072/1616
- ^ http://www.archaeology.org/interactive/hierakonpolis/field/hair.html
- ^ Department of Dermatology, Academic Teaching Hospital Dresden-Friedrichstadt. "Eyebrow colour in diabetics". Acta Dermatovenerol Alp Panonica Adriat. PMID 16435045.
{{cite journal}}: Unknown parameter|Date=ignored (|date=suggested) (help); Unknown parameter|Pages=ignored (|pages=suggested) (help) - ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3288386&dopt=Abstract
- ^ Rogers, Alan R., Iltis, David & Wooding, Stephen (2004). "Genetic variation at the MC1R locus and the time since loss of human body hair". Current Anthropology. 45 (1): 105–108.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Valverde P, Healy E, Jackson I, Rees JL, Thody AJ. Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans. Nature Genetics . 1995 Nov;11(3):328-30.