Human hair color
Human hair color is the pigmentation of
Genetics and biochemistry of hair color
The full genetic basis of hair color is complex and not fully understood.[1] Regulatory DNA is believed to be closely involved in pigmentation in humans in general,[2] and a 2011 study by Branicki et al. identified 13 DNA variations across 11 different genes that could be used to predict hair color.[3]
Two types of pigment give hair its color, black-brown
Different hair color
Pheomelanin colors hair
Natural hair colors
Blond | Dark blond | Medium brown | Dark brown | Reddish-brown | Red | Black | Gray | White |
Natural hair color can be black, brown, red and blonde.[10]
Color shade scale
The
Image gallery
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Natural black hair
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Dark brown hair
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Medium brown hair
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Light brown hair
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Chestnut brown hair
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Light chestnut brown hair
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Orange red hair
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Copper hair
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Strawberry blond hair
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Light blond hair
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Golden blond hair
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Medium blond hair
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Grey hair
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White hair
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White hair caused by albinism
Black hair
Black hair or jet black hair is the darkest hair color. It has large amounts of eumelanin and is more dense than other hair colours and is the commonly seen hair color in Asia and Africa due the fact that the people in these regions tend to have lower levels of tyrosinase in their bodies. Black eumelanin secretion causes the hair to turn black, which indicates that the MC1R is in the active state. Jet black hair, the darkest shade will not have a warm, neutral tone but a sheen which can seem almost blue, like the iridescence of a raven's wing; hence, sometimes referred to as raven-black. Jet black hair appears to have reflective silver color in bright sunlight.[12][13]
Brown hair
Brown hair is the second most common human hair color, after black. Brown hair is characterized by higher levels of eumelanin and lower levels of pheomelanin. Of the two types of eumelanin (black and brown), brown-haired people have brown eumelanin; they also usually have medium-thick strands of hair. Brown-haired girls or women of European, West Asian or North African descent are often known as brunettes.
Chestnut hair is a hair color which is a reddish shade of brown hair. In contrast to auburn hair, the reddish shade of chestnut is darker. Chestnut hair is common among the native peoples of Northern, Central, Western, and Eastern Europe and is also found in
Auburn hair
Auburn hair ranges along a spectrum of light to dark red-brown shades. The chemicals which cause auburn hair are
Red hair
Red hair ranges from light strawberry blond shades to
Blond hair
Blond (sometimes blonde for women) hair ranges from pale white (platinum blond) to dark gold blond. Strawberry blond, a mixture of blond and red hair, is a much rarer type containing the most
Gray and white hair
Gray or white hair is not caused by a true gray or white pigment, but is due to a lack of pigmentation and melanin. The clear hairs appear as gray or white because of the way light is reflected from the hairs. Gray hair color typically occurs naturally as people age (see aging or achromotrichia below).
In some cases, gray hair may be caused by thyroid deficiencies,
Europeans often begin to grow gray hairs in their mid-30s while Asians begin graying in their late 30s, but most Africans retain their original hair color until their mid-40s. Permanently white hair starting in childhood can be genetically inherited, but unlike albinism, there are no negative medical implications. The trait follows X-linked recessive inheritance, and so is more common in men, and women can be carriers without being affected.[21][22]
Graying is a gradual process; according to a study by
Conditions affecting hair color
Aging or achromotrichia
Children born with some hair colors may find it gradually darkens as they grow. Many blond, light brown, or red haired infants experience this. This is caused by genes being turned on and off during early childhood and puberty.[27]
Changes in hair color typically occur naturally as people age, eventually turning the hair gray and then white. This is called achromotrichia. Achromotrichia normally begins in the early to mid-twenties in men and late twenties in women. More than 60 percent of Americans have some gray hair by age 40. The age at which graying begins seems almost entirely due to genetics. Sometimes people are born with gray hair because they inherit the trait.[28]
The order in which graying happens is usually: nose hair, hair on the head, beard, body hair, eyebrows.[29]
In non-balding individuals, hair may grow faster once it turns gray.
Several genes appear to be responsible for the process of graying. Bcl2 and Bcl-w[32] were the first two discovered, then in 2016, the IRF4 (interferon regulatory factor 4) gene was announced after a study of 6,000 people living in five Latin American countries. However, it found that environmental factors controlled about 70% of cases of hair graying.[33]
The change in hair color occurs when melanin ceases to be produced in the hair root and new hairs grow in without pigment. The
Graying of hair may be triggered by the accumulation of hydrogen peroxide and abnormally low levels of the enzyme catalase, which breaks down hydrogen peroxide and relieves oxidative stress in patients with vitiligo. Since vitiligo can cause eyelashes to turn white, the same process is believed to be involved in hair on the head (and elsewhere) due to aging.[34][unreliable source?]
The anti-cancer drug imatinib has recently been shown to reverse the graying process.[35] However, it is expensive and has potentially severe and deadly side effects, so it is not practical to use to alter a person's hair color. Nevertheless, if the mechanism of action of imatinib on melanocyte stem cells can be discovered, it is possible that a safer and less expensive substitute drug might someday be developed. It is not yet known whether imatinib has an effect on catalase, or if its reversal of the graying process is due to something else.[36]
Stress
Anecdotes report that stress, both chronic and acute, may induce achromotrichia earlier in individuals than it otherwise would have.[37] Proponents point to survivors of disasters, such as Titanic survivor Harold Bride and prisoner of war John McCain, as well as high-level politicians such as Bill Clinton and Barack Obama. There is some evidence for chronic stress causing premature achromotrichia,[38] but no definite link has been established. It is known that the stress hormone cortisol accumulates in human hair over time, but whether this has any effect on hair color has not yet been resolved.[39] A 2020 paper, published in the journal Nature reported that stress can cause hair to lose its pigment. An overactive immune response can destroy melanocytes and melanocyte stem cells in black-haired rats. When intentionally subjecting them to panic, they bleached their coat. The next time the rats' coat grew, there were no melanocyte stem cells in these damaged follicles, so white hairs sprouted, and the color loss was permanent.[40]
UV damage
Excessive exposure to the sun is the most common cause of structural damage of the hair shaft. Photochemical hair damage encompasses hair protein degradation and loss, as well as hair pigment deterioration[41] Photobleaching is common among people with European ancestry. Around 72 percent of customers who agreed to be involved in a study and have European ancestry reported in a recent 23andMe research that the sun lightens their hair. The company also have identified 48 genetic markers that may influence hair photobleaching.[42]
Medical conditions
Albinism is a genetic abnormality in which little or no pigment is found in human hair, eyes, and skin. The hair is often white or pale blond. However, it can be red, darker blond, light brown, or rarely, even dark brown.
Malnutrition is also known to cause hair to become lighter, thinner, and more brittle. Dark hair may turn reddish or blondish due to the decreased production of melanin. The condition is reversible with proper nutrition.
Werner syndrome and pernicious anemia can also cause premature graying.
A 2005 uncontrolled study demonstrated that people 50–70 years of age with dark eyebrows but gray hair are significantly more likely to have
Artificial factors
A 1996
Gray 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 graying.[46]
There are no special diets, nutritional supplements, vitamins, or proteins that have been proven to slow, stop, or in any way affect the graying process, although many have been marketed over the years. However, French scientists treating leukemia patients with imatinib, a drug used in treating cancer, noted an unexpected side effect: some of the patients' hair color was restored to their pre-gray color.[36]
Changes after death
The hair color of buried bodies can change. Hair contains a mixture of black-brown eumelanin and red-yellow pheomelanin. Eumelanin is less chemically stable than pheomelanin and breaks down faster when oxidized. The color of hair changes faster under extreme conditions. It changes more slowly under dry oxidizing conditions (such as in burials in sand or in ice) than under wet reducing conditions (such as burials in wood or plaster coffins).[47]
Hair coloring
Hair color can be changed by a chemical process. Hair coloring is classed as "permanent" or "semi-permanent".
Permanent hair color means that the hair's structure has been chemically altered until it is eventually cut away. This does not mean that the synthetic color will remain permanently. During the process, the natural color is removed, one or more shades, and synthetic color has been put in its place. All pigments wash out of the cuticle. Natural color stays in much longer and artificial will fade the fastest (depending on the color molecules and the form of the dye pigments).
Permanent hair color gives the most flexibility because it can make hair lighter or darker as well as changing tone and color, but there are negatives. Constant (monthly or six-weekly) maintenance is essential to match new hair growing in to the rest of the hair, and to remedy fading. A one-color permanent dye creates a flat, uniform color across the whole head, which can look unnatural and harsh, especially in a fair shade. To combat this, the modern trend is to use multiple colors—usually one color as a base with added highlights or lowlights in other shades.
Semi-permanent color washes out over a period of time—typically four to six weeks, so root regrowth is less noticeable. The final color of each strand is affected by its original color and porosity, so there will be subtle variations in color across the head—more natural and less harsh than a permanent dye. However, this means that gray and white hair will not dye to the same color as the rest of the head (in fact, some white hair will not absorb the color at all). A few gray and white hairs will blend in sufficiently not to be noticeable, but as they become more widespread, there will come a point where a semi-permanent alone will not be enough. The move to 100% permanent color can be delayed by using a semi-permanent as a base color, with permanent highlights.
Semi-permanent hair color cannot lighten hair.[48] Hair can only be lightened using chemical lighteners, such as bleach. Bleaching is always permanent because it removes the natural pigment.
"Rinses" are a form of temporary hair color, usually applied to hair during a shampoo and washed out again the next time the hair is washed.
See also
References
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