When I’m about to deliver some bad news, I often advise people to take a deep breath. This time, that would be bad advice. According to the World Health Organization, the air people breathe in many parts of the world needs to be labeled as carcinogenic to humans. “Depending on the level of exposure in different parts of the world, the risk was found to be similar to that of breathing in second-hand tobacco smoke.”

+ Quartz: Here are the world’s worst cities for air pollution, and they’re not the ones you’d expect.