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Greying of hair, also known as greying, canities, or achromotrichia, is the progressive loss of pigmentation in the hair, eventually turning the hair grey or white which typically occurs naturally as people Ageing.
The order in which greying happens is usually: nose hair, hair on the head, beard, body hair, eyebrows.
Greying is a gradual process; according to a study by L'Oreal, overall, of those between 45 and 65 years old, 74% had some grey hair, covering an average of 27% of their head, and approximately 1 in 10 people had no grey hairs even after the age of 60.
The change in hair colour occurs when melanin ceases to be produced in the hair root and new hairs grow in without pigment. The at the base of produce , the cells that produce and store pigment in hair and skin. The death of the melanocyte stem cells causes the onset of greying. It remains unclear why the stem cells of one hair follicle may fail to activate well over a decade before those in adjacent follicles less than a millimeter apart.
In non-balding individuals, hair may grow faster once it turns grey. Unlike in the skin where pigment production is continuous, melanogenesis in the hair is closely associated with stages of the hair cycle. Hair is actively pigmented in the anagen phase and is "turned off" during the catagen phase, and absent during telogen.Slominski A, Paus R. Melanogenesis is coupled to murine anagen: Toward new concepts for the role of melanocytes and the regulation of melanogenesis in hair growth. J Invest Dermatol. 1993;101:90S–7S Thus, a single hair cannot be white on the root side, and colored on the terminal side.
Several appear to be responsible for the process of greying. Bcl2 and Bcl-w 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 countries. However, it found that environmental factors controlled about 70% of cases of hair greying.
Greying 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.
In some cases, grey hair segments due to stress, chemicals, or a nutrient deficiency may reverse when the issue resolves.
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.
Vitiligo is a patchy loss of hair and skin color that may occur as the result of an auto-immune disease. In a preliminary 2013 study, researchers treated the buildup of hydrogen peroxide which causes this with a light-activated pseudo-catalase. This produced significant media coverage that further investigation may someday lead to a general non-dye treatment for grey hair.
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 greying.
A 2005 uncontrolled 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 hair.
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.
There are no special diets, nutritional supplements, vitamins, or proteins that have been proven to slow, stop, or in any way affect the greying 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-grey color.
The Chemotherapy imatinib has been shown to reverse the greying process. However, it is expensive and has potentially severe side effect such as fluid retention, gastrointestinal bleeding, bone marrow suppression, liver problems, and heart failure, 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 greying process is due to something else.
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