Millions of people awoke this week to hazy skies and a dim red sun, its light filtered through smoke released by one of Canada’s worst, and earliest, wildfire seasons on record. More than 400 fires are currently burning in the country, leading to smoke conditions across Canada and in much of the U.S.

As of Wednesday afternoon, New York City had some of the worst air pollution of any city in the world.

Wildfire exposure is bad for the human body no matter how healthy a person is or how long they’re exposed to it, and public health officials across the U.S. and Canada are urging people to take precautions. "Wildfire smoke absolutely puts your health at risk,” said Kimberly Humphrey, an emergency physician from Australia who is now a climate change and human health fellow at Harvard University.