According to the Library of Congress, your chances of going gray increase by as much as 20 percent every year after you turn 30. The hair on your head grays before the rest of your body hair, and you'll usually spot a few gray hairs around your temples before the gray hair starts spreading toward your scalp, according to the University of Maryland Medical Center (UMMC).
The Basics
Gray hair isn't hair that has changed colors--it's actually hair that has lost color. In normal, nongray hair, cells in your hair produce a pigment called melanin that they inject into your hair shaft to give it color--eumelanin creates darker colors, while phaeomelanin gives a lighter range of hair color. When your hair turns gray, it's because the cells that produce pigment die or stop making melanin so that your hair's pigment gradually fades away.
Causes
Several factors play a role in causing pigment-producing cells to stop working. Age, of course, is one of them, and many people associate gray hair with aging. But genetic factors, hormonal levels and exposure to pollution, chemicals and extreme weather can also slow melanin production in your hair, according to the Library of Congress.
Theories/Speculation
Researchers aren't sure what happens to trigger the slowdown in melanin production that causes gray hair. Based on the fact that the roots of hair are always pale, Desmond Tobin, professor of cell biology from the University of Bradford in England, theorizes that all hair has an internal biological clock that cues the cells to stop producing pigment. Gray hair may even be caused by a natural bleaching process, suggests a study published in 2009 in the Journal of the Federation of American Societies for Experimental Biology, which found that hair's natural production of hydrogen peroxide is unchecked as people age because the enzymes that block bleaching stop working.
Misconceptions
Though over time, stress may contribute to gray hair, there's no evidence that a sudden shock or fear can turn your hair gray, according to KidsHealth.org, an online health information resource maintained by the Nemours Foundation. Your genes determine how fast your hair turns gray, but there usually is at least 10 years between spotting the first gray hairs and full-blown gray hair.
Expert Insight
Gray hair reflects light, so keeping it in top shape is key to looking good, celebrity hair stylist Mark Garrison says in Ladies Home Journal. Garrison suggests looking for clarifying, moisturizing shampoos and conditioners that leave a bluish tint on hair so it doesn't end up looking yellow and dingy--a common problem for gray hair. If you're nervous about using blue-tinted shampoo, Garrison recommends mixing the tinted shampoo with regular moisturizing shampoo to find a color intensity you like.
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