Though some people maintain their colorful locks for many years, the unfortunate truth is that everybody eventually goes gray. Even though graying is a universal and seemingly simple rite of passage, much of the process remains a puzzle that scientists are continuously trying to solve.
Hair Pigment Basics
In an article for Scientific American, Dr. Laurence Meyer, a dermatologist at the University of Utah, explains how hair color works. He notes that inside every hair follicle are specialized cells called melanocytes, which are filled with a pigment called melanin, which comes in two forms: eumelanin, which is a dark, black-brown pigment, and pheomelanin, which is a light, yellow-red pigment. The unique combination and distribution of these two pigments is what determines both your hair and skin color.
Causes
According to Meyer, at some point during the aging process, melanocytes simply "switch off" and stop producing melanin. Eventually, these specialized cells begin to disappear. Initially, this tends to occur in random hairs, usually starting around the temples and forehead. Hairs with low amounts of melanin are gray, while those with no melanin at all are white.
Time Frame
Some people gray as early as their teen years, while others don't find a single strand until their 40s or even later. Most people, however, begin graying in their 30s. Meyer notes that 50 percent of 50-year-olds are 50 percent gray or more. Caucasians gray the earliest, followed by Asians and Africans.
Theories/Speculation
Because different races and ethnic groups gray differently, and because gray hair has been shown to follow similar patterns among related family members, it is widely agreed that genetics play a large role in when and how hair turns gray. However, scientists are unclear on why hair ages the way it does, and what catalyst prompts the graying process. Recent studies have led to different theories that may unlock some of gray hair's mysteries. One theory comes from a 2009 study performed by a group of European researchers and published in the Federation of American Societies for Experimental Biology Journal, or FASEBJ. The team noted that every hair produces small amounts of hydrogen peroxide, and that an enzyme called catalase usually breaks the hydrogen peroxide down. The team theorized that diminished catalase causes a buildup of hydrogen peroxide, which impedes melanin production and bleaches the hair from the inside out. Another theory posed by Harvard scientists in a 2005 Science magazine article says melanocyte stem cells--immature melanocyte cells that replace mature cells when they die--slow and then stop their production as the body ages. Eventually, no stem cells are left to replace aging melanocyte cells. Why the stem cells stop production isn't known.
Misconceptions
Most people believe stress causes gray hair, or at least causes hair to gray faster. However, no current scientific evidence supports this. In addition, though it is widely thought that graying early is a sign of early aging, a Copenhagen study of 20,000 men and women cited by the New York Times found no correlation between graying earlier and dying earlier, or experiencing early aging symptoms such as wrinkles, age-related heart disease or baldness.
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