Graying hair is an inescapable part of growing older for most. The 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 but the number one cause is so obvious it has been verified without scientific research:
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