I did not know that yesterday!

Many of us point to our jobs as the reason for gray hair, but we sought the biological cause of those pesky reminders of our own mortality. We typed "gray hair cause" into the Yahoo! search box and set off in search of some answers. We clicked around and learned the ugly truth about gray hair.

When our bodies are functioning well, cells in our hair follicles called melanocytes generate pigments -- the chief one being melanin. When the melanocytes stop producing these pigments, we sprout a transparent hair, which appears as an unsightly gray due to the color of the dead cells that comprise the strand.

Why does this happen? The most common reason is heredity; premature gray hair is yet another thing we can blame on our parents. But there are also several medical conditions characterized by graying of the hair. A B-12 deficiency, a thyroid imbalance, and anemia can all cause premature gray hair. And if you needed yet another reason to quit smoking, there is new evidence that smokers are four times more likely to go gray at a young age.

The common belief that psychological shock or trauma can turn hair gray overnight is cause for a fair amount of controversy. While some people claim such an occurrence, many scientists question the actual time frame involved.

Source: ask.yahoo.com