En español | Graying hair is an inescapable part of growing older for most, as those first strands of silver appear to sprout for many people in their mid-30s — and by age 50 it's not unusual for half their hair to be gray.
Known by scientists as canities or achromotrichia, the graying of hair is a long-studied phenomenon that has a variety of causes. First, the good news: It's not going to kill you. In a 1998 study published in The Journals of Gerontology, researchers found no correlation between the mortality and the extent of graying of the hair among a random sample of 20,000 participants in a long-term cardiovascular study launched in 1975 in Copenhagen, Denmark.
But why do we go gray?
Hairs appear to the naked eye as white, silver or gray absent the pigments that otherwise provide color in shades of black, brown, blond or red.
Within each hair follicle are cells, known as melanocytes, that produce one of two basic pigments — eumelanin or pheomelanin, depending on your DNA. Eumelanin is commonly present in black and brown hair, while pheomelanin is found in red, auburn and blond hair.
Unlike the melanin that colors skin, the pigments produced in scalp hairs typically degrade more slowly – allowing for the hair to keep its color as it grows out over an average of 3.5 years, according to a 2020 article in the journal Skin Appendage Disorders.
Gray hair develops as melanocytes decrease in number, but exactly when those cells begin to wane differs for each individual. However, there are some general trends. According to the article, “graying typically begins in the mid-30s for Caucasians, the late-30s for Asians, and the mid-40s for Africans."
In your genetic code
Scientists have found specific genes related to graying hair. In a 2016 study published in Nature Communications, a team of researchers from University College London (UCL) identified the interferon regulatory factor 4 (IRF4) gene as being responsible for regulating production and storage of melanin.
"We have found the first genetic association to hair graying, which could provide a good model to understand aspects of the biology of human aging,” Andrés Ruiz-Linares, a professor in the UCL Department of Genetics, Evolution & Environment who led the study, said in a statement. “Understanding the mechanism of the IRF4 graying association could also be relevant for developing ways to delay hair graying."
While you can't change your genetics or turn back the clock, there are other factors at play in graying hair that may be within your control.
A 2018 study published in the Journal of Cosmetic Dermatology found that among 1,192 volunteers between ages 18 and 20, those with premature hair graying (PHG) were more likely to have a family history of PHG, have a genetic tendency to develop allergic diseases such as eczema or asthma, or be vegetarian. To a lesser extent, they were also more likely to be overweight or report having higher levels of stress in their lives. The study suggests that it may be possible to prevent graying, or at least slow it down, through changes in diet, maintaining a normal weight and decreasing alcohol consumption.
Researchers at the Mayo Clinic in Rochester, Minnesota, also suggest that some causes of premature hair graying are reversible. In a 2018 article published in the International Journal of Trichology, they noted that a deficiency of vitamin B12 can cause premature graying, which could be reversed through supplements. Common natural sources of vitamin B12 are dairy products and meat, which may explain why a vegetarian diet could be a factor in PHG. Older adults may also often have difficulty absorbing vitamin B12 through digestion. In one study, 55 percent of patients with pernicious anemia (a condition caused by a lack of vitamin B12) had PHG, compared to 30 percent in the control group, the Mayo researchers noted.
Smoking has long been considered a factor in premature graying, according to a 2013 study that confirmed the association among Middle Eastern men and women living in Jordan. The study, published in the Indian Dermatology Online Journal, found that among 207 study participants, smokers were substantially more at risk of PHG than nonsmokers.
The researchers could not say with certainty why smoking affects hair color but suggested that it could increase “oxidative stress” that damages melanin-producing cells, noting that melanocytes in gray hair bulbs frequently show common signs of such damage.
Researchers at Harvard University have found that stress can accelerate the graying process and have determined the biology behind the phenomenon — at least in laboratory mice.
Ya-Chieh Hsu, a cellular biologist at Harvard, and her fellow researchers suggest that stresses that trigger a fight-or-flight response may deplete the stockpile of stem cells in hair follicles that can be converted into pigment cells when new hairs form. In experiments on mice, they found such hair-raising experiences activated stem cells. “After just a few days, all of the pigment-regenerating stem cells were lost. Once they're gone, you can't regenerate pigments anymore,” Hsu said in a statement. “The damage is permanent."
Particular diseases can cause premature graying, including vitiligo and alopecia areata, according to Robert H. Shmerling, M.D., senior faculty editor of Harvard Health Publishing.
Vitiligo occurs when cells that produce melanin die or stop functioning, resulting in a loss of skin color in patches over the body that usually grow over time. In some cases, it also causes hair to lose color. With alopecia areata, patches of hair — especially colored hairs — can be suddenly lost, which may result in more noticeable gray hair. Shmerling noted in a 2017 article that the result could explain why some people seem to turn gray overnight.
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Cures for graying hair
Trying to solve the puzzle of graying hair is as old as history. Clay tablets from the ancient Assyrian Empire (7th century B.C.) include medical texts (written in cuneiform) describing a means to darken prematurely gray hair by applying — often for days at a time — various mixtures of ingredients that included: cypress oil, leek seeds, poppyseeds, pine gum, the head of a black raven or gall from a black ox.
Researchers continue to look for a way to reverse the graying process, but so far with little success. Some medications have been reported, in rare cases, to restore pigmentation in gray hair but the evidence is of “low quality” and the medications may have damaging side effects, making them difficult to study for an essentially cosmetic purpose. But they do offer some hope, perhaps shedding light on “possible mechanisms to target” for future studies, according to Yale.