Who's to blame for those gray hairs?

Can you blame a lifetime of annoying jobs, unruly kids and family emergencies for your silverstreaked head of hair?

It turns out that those ever-multiplying graying hairs that tend to crop up with age really are signs of stress, according to new research recently published in the science and medical journal, "Cell."

However, the stress in question is stress on cells in your body, not necessarily the family and work stress over your lifetime.

According to researchers at Tokyo Medical and Dental University, the DNA in the body's cells is under constant attack from such damaging agents as chemicals, ultraviolet light and ionizing radiation.

"It is estimated that a single cell in mammals can encounter approximately 100,000 DNA damaging events per day," said Emi Nishimura, who led the new research.

It turns out that stress does damage to the DNA in stem cells that are responsible for the coloring in our hair, among other things.

According to the researchers, the new findings about gray hair may lead to advances in understanding other symptoms of aging. They support the "stem cell aging hypothesis," which proposes that DNA damage to long-lived stem cells can be a major cause for the symptoms that come with age.