The Cause Of Gray Hair?

As I've been graying (and balding) over the last several years, I've often wondered why hair color changes.

Scientists looking for a cure for skin cancer have stumbled on something else: the reason why hair turns gray.

It turns out that one of the most common signs of aging occurs because of the death of stem cells that spawn the pigment-manufacturing cells called melanocytes, the scientists said. As the supply of new pigment is cut off, hair turns gray.

And here I thought the cause might be teenagers -- in particular those in my last class of the day.