Why Does Hair Turn Gray With Age?

It is readily apparent that hair turns gray with age, and while scientists partially understand why this happens, some aspects of this natural process remain a mystery. Unraveling this mystery may have medical implications that reach far beyond the cosmetic benefits of a gray hair cure, according to an article in the New York Times, as scientists are optimistic that the as-of-yet unknown causes may bring us closer to a cure for skin cancer and other diseases.

Graying Process

According to Scientific American, the graying process begins in the follicle of each individual hair, given enough time. A follicle is a small duct in the skin in which cells called keratinocytes grow and join together to form a strand of hair at the root. As the keratinocytes continue to grow, the hair gets longer and is supplied with a natural pigment called melanin from nearby melanocyte cells. Melanin is what gives hair its color, and it comes in two types: eumelanin, which produces darker shades, and pheomelanin, which produces lighter shades. With age, melanocytes produce less and less melanin, resulting in gray hairs. Eventually, the melanocytes may cease melanin production altogether, resulting in white hairs.

Genetics

While graying is generally unavoidable over a long enough lifetime, some people start noticing gray hairs at younger ages than others. According to The New York Times, a person's genetic makeup is believed to be largely responsible for this variation. It reports that a 2005 article from the Journal of Investigative Dermatology cites heredity as the primary determining factor in the age of graying, and quotes researchers who note that genetics bestow some people with dark hair well into old age.

Hydrogen Peroxide

A Science Daily article published in 2009 cites a study conducted by European researchers that produced a new theory on graying that involved hydrogen peroxide. The study was investigating the causes of vitiligo, a genetic condition that causes patches of skin to lose pigment. It was discovered that vitiligo sufferers exhibited weak activity of an enzyme called catalase, which metabolized hydrogen peroxide, a naturally occurring pigment bleacher. The researchers noted that hydrogen peroxide is naturally produced in hair follicles in small amounts, but that it accumulates over the years, effectively bleaching hairs from the inside out.

Unproven Theories

While genetics and hydrogen peroxide levels may both be significant factors in the graying process, there may be even more factors in play, according to Scientific American. Jokes are often made about how stress from work, children and other stressors can cause grayness, and while this is not yet proved by science, it is not disproved, either. David Fisher, professor of pediatrics at Harvard Medical School, indicates that stress can affect hormone levels, and hormones may in turn affect the melanin production of melanocytes. Another theory suggests that free radical production, which occurs as a natural byproduct of numerous metabolic processes, may also inhibit the long-term ability of melanocytes to produce melanin.

Complicating Factors

Factors unrelated to age may also affect when and how quickly a person goes gray. A study published by the Journal of the Medical Association of Thailand in 1991 found that vitamin B-12 deficiency can cause premature graying. The Journal of Investigative Dermatology also reports that ethnicity is a factor; whites often go gray at the youngest ages, followed by Asians, with Afro-ethnic populations often keeping their pigment the longest.