We already know air pollution is bad for our lungs. But a new study suggests it's also bad for our brains.
Researchers said breathing polluted air can result in a "steep reduction in verbal and math scores."
The study, published in the Proceedings of the National Academy of Sciences, found air pollution led to cognitive problems, particularly in older men.
Those cognitive problems can lead to dementia and other mental health concerns.
The data is based on nearly 32,000 people over a four-year period in China.
"The damage on the aging brain by air pollution imposes substantial health and economic costs ..." researchers said.
According to the World Health Organization, nine out of every 10 people on the planet breathe air containing a high level of pollutants, with Africa and Asia being the worse affected regions.