You might not be able to see it or feel it, but air pollution can harm your brain and stress the body. Air pollution is the largest environmental health risk in the world, responsible for millions of premature deaths every year.

Air pollution tends to pose the biggest risk to the very old, to the very young and to people already suffering from some chronic ailments. What types? Asthma and heart disease are two major conditions that put people at risk.

But scientists are learning that air pollution can pose serious risks to anyone. You don’t have to be old or sick. You don’t have to suck in horrible fumes or air so full of pollutants that you can see and taste them.

Cities have seen worsening air quality in part due to wildfires and rising temperatures, since heat is one component of ozone.