Secondhand smoke rears its ugly head once again -- this time in the form of study results revealing high levels of secondhand smoke in the workplace can double the risk of lung cancer for non-smokers.

Researchers at the University of Illinois at Chicago looked at results from 22 studies conducted in the United States, Canada, Europe, India, Japan, and China. What they found -- and published in the American Journal of Public Health -- is a lung cancer risk 50 percent higher than normal for non-smokers exposed to smoke on the job for more than 30 years. They also found risk increases with level of exposure.

"We believe that our study provides the strongest evidence to date that smoking in the workplace does present a substantial risk to workers -- and particularly to workers who are working in highly exposed areas such as bar workers or restaurant workers," lead researcher Leslie Stayner said.

Previous evidence for increased lung cancer risk caused by secondhand smoke comes from studies of non-smokers married to smokers.

Secondhand smoke -- also known as passive smoke and environmental tobacco smoke -- is smoke from a cigarette, pipe, or cigar as well as smoke exhaled from the lungs of smokers and inhaled by non-smokers. It can cause cancer, respiratory problems, and asthma in non-smokers and is leading to increased efforts by communities to ban or limit smoking in the workplace.

This week in France, bans begin in offices, stores, schools, and hospitals. Come January 2008, cafes and restaurants must also comply with bans. For now, smoking in these areas is permitted in hermetically sealed rooms without any services.