Outdoor air pollution has been officially classified as carcinogenic by the cancer arm of the World Health Organisation.
The International Agency for Research on Cancer (IARC) said air pollution from traffic and industrial fumes was a definite cause of lung cancer and also linked to bladder cancer. The strong verdict from IARC, a cautious body that pronounces only when the evidence is strong, will put pressure on governments to take action.
"The air we breathe has become polluted with a mixture of cancer-causing substances," said Dr Kurt Straif, head of the IARC monographs section, which assesses evidence and publishes official warnings. "We now know that outdoor air pollution is not only a major risk to health in general, but also a leading environmental cause of cancer deaths."
Air pollution is already known to increase the risks for other diseases, including heart and respiratory disease. The numbers of those exposed to air pollution have risen rapidly as countries have industrialised. The most recent data suggests there were 233,000 deaths from lung cancer caused by air pollution around the world in 2010.