It was once scientific heresy to suggest that smoking contributed to lung cancer. Now, another idea initially dismissed as nutty is gaining acceptance: the graveyard shift might increase your cancer risk.

Next month, the International Agency for Research on Cancer, the cancer arm of the World Health Organization, will classify shift work as a "probable" carcinogen.

That will put shift work in the same category as cancer-causing agents like anabolic steroids, ultraviolet radiation, and diesel engine exhaust.