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Diesel exhaust is associated with an increased risk of lung cancer, according to a press release issued by the World Health Organization (WHO).[1]

The announcement came after a group of international experts gathered for a weeklong meeting to review the evidence. As a result of that review, the International Agency for Research on Cancer (IARC), a scientific working group of the WHO, has classified diesel exhaust as a carcinogen based on sufficient evidence that exposure to the exhaust is associated with an increased risk for lung cancer and bladder cancer. A report highlighting the data was published early online in the Lancet Oncology.[2]

Much of the evidence reviewed by the group focused on people with occupational exposure to diesel exhaust, such as railway workers, bus drivers, and underground miners. The evidence indicates that occupational exposure may be associated with a significantly increased risk—for example, miners may have a two- to three-fold increased risk of developing lung cancer, railroad workers may have a 40 percent increased risk, and truck drivers may have a 15-40 percent increased risk.

Evidence for non-occupational exposure is more limited; however, the experts concluded that exposure still poses a risk for the general population and thus, the classification as a carcinogen extended to all exposure, including traffic exhaust for the general population. With most carcinogens, the risk is associated with dose; however, diesel exhaust appears to be a public health issue—regardless of dose.

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In short, after reviewing the evidence, the experts unanimously agreed that there was now sufficient evidence to classify diesel exhaust as a group one human carcinogen—in contrast to a more ambiguous 1988 conclusion that it was “probably” a carcinogen. It is not clear how much exposure is needed to increase the risk. Now that it is classified as a carcinogen, it will be up to governments to make regulatory decisions regarding diesel exhaust.


[1] International Agency for Research on Cancer: Diesel engine exhaust carcinogenic. [World Health Organization Press Release]. Available at:

[2] Carcinogenicity of diesel-engine and gasoline-engine exhausts and some nitroarenes. The Lancet Oncology. Published online June 15, 2012. DOI:10.1016/S1470-2045(12)70280-2

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