June 15th, 2009
10:12 AM ET

Is radiation causing prematurely gray hair?

By Madison Park
CNNHealth Writer

I was 22 years old when I plucked a gray strand from my tangled black hair.

I showed my mom the strange silver hair, and she shot me the "I-told-you-so" look.  She always told me that watching TV or being on the computer  would make me prematurely gray.

Her evidence: Every computer engineer she knew got gray in her 30's, but she only knew one computer engineer. So I dismissed this as a kooky theory.

But my gray encounter sparked a curiosity. I’ve seen an occasional silver strand and sometimes a scattering of gray hairs on students, teens and even kids.  One mother wrote to CNNhealth after spotting a strand of gray hair on her 3½-year-old daughter.

Could younger people be graying earlier?  Could it be hereditary or are there environmental factors - like  TVs and computer screens– as my mother suggested?

While researchers have no definitive answers, scientists in Japan say that "genotoxic stress" damages cells which are responsible for hair color. When these melanocyte stem cells die, we get irreversible graying, according to a report released this month in the journal Cell.

Our DNAs are under constant attack by chemicals, ultraviolet light and ionizing radiation, said one of the authors, Dr. Emi Nishimura of Kanazawa University.

In nature, ionizing radiation can come from cosmic rays from the sun and stars, and radioactive materials in rocks and soil, according to the National Institutes of Health. But ionizing radiation also comes from man-made sources, such as X-rays, televisions, smoke detectors, building materials, tobacco smoke, and mining and agricultural products, such as granite, coal, and potassium salt.

"It is estimated that a single cell in mammals can encounter approximately 100,000 DNA damaging events per day,” Nishimura wrote in an email. "But is not clear which kind of sources for genotoxic stress are the major contributors to aging or hair graying."

In Nishimura’s experiment, 7-to-8-week-old brown and black mice were exposed to whole-body X-rays. "If we try lower doses (of ionizing radiation), you can see a salt and pepper pattern in their hair," Nishimura said.  "With a bit higher doses, you can see more white hair.  Most of the hair became white."

While studies in mice don't always apply to humans, they can provide scientific clues.

“We discovered that hair graying, the most obvious aging phenotype, can be caused by the genomic damage response" wrote the researchers from the Center for Cancer and Stem Cell Research at Kanazawa University in Japan. The results on mice "suggest that physiological hair graying can be triggered by the accumulation of unavoidable DNA damage."

I haven't seen another gray hair in years, but I'm on the lookout.

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Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.