It's easy to see how air pollution could affect people with respiratory problems.
But could bad air also cause ear infections?
A new study suggests children who live in areas with moderate air pollution have a higher risk of middle-ear infections than those who breathe cleaner air.
Researchers tracked more than 45,000 Canadian children from birth to age 2, who visited the doctor for middle-ear infections, a common ailment in young kids.
They analyzed air-quality data in each child's neighborhood, to determine their exposure to pollutants. Then they looked at the relationship between their ear infections and their air-pollution exposure, to determine their exposure to pollutants.
Then they looked at the relationship between their ear infections and their air-pollution exposure.
Forty-two percent saw the doctor at least once.
But kids living in areas with the most traffic pollution were 10 percent more likely to see the doctor than those living in areas with the least.
And children breathing the highest levels of wood smoke were 32 percent more likely to see the doctor.
More research is needed to confirm the link.