People wear masks in Chicago on Thursday to protect themselves from smoke from the Canadian wildfires. City officials are encouraging people to stay indoors as data shows Chicago has some of the worst air quality of any major city in the world. Scott Olson/Getty Images hide title toggle title Scott Olson/Getty Images One version of
People wear masks in Chicago on Thursday to protect themselves from smoke from the Canadian wildfires. City officials are encouraging people to stay indoors as data shows Chicago has some of the worst air quality of any major city in the world.
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One version of this story was originally published on January 8, 2025. It has been updated to reflect the wildfires currently bringing smoke to the US.
Smoke from wildfires in Canada and Minnesota prompted more air quality alerts Friday in the Northeast and Mid-Atlantic United States, as well as the Upper Midwest.
Michigan received a statewide air quality advisory on Wednesday, and Minnesota’s air quality reached the dangerous “purple” alert level. Wildfire smoke is breaking records in Wisconsin and turning the sky orange in Vermont. And after a brief respite on Friday morning, New York City will see more smoke.
Exposure to wildfire smoke is a growing health issue across the country, as human-caused climate change increases the risk and intensity of wildfires and smoke that can travel thousands of miles downwind.
Here’s what you need to know about the health risks and how to protect yourself.
The health risks of breathing wildfire smoke
May-Lin Wilgus, a pulmonologist and professor at UCLA, compares breathing wildfire smoke to smoking cigarettes: a lot of cigarettes.
Scientists track air quality with the Air Quality Index, or AQI, which incorporates different sources of pollution such as ozone and fine particulate matter. Many scientists do not believe there is a “safe” AQI level because the measurement does not capture many harmful contaminants, but below 50 is often considered acceptable. Higher numbers indicate air pollution that is more harmful to health.
As of Friday morning, the AQI in Detroit was 435, the worst for any major city in the world. On a smoky day, when AQI levels reach between 100 and 200, “exposure to fine particulate matter, air pollution, is similar to smoking a quarter to a half pack a day,” Wilgus says.
That exposure takes its toll on a healthy person. But it’s particularly harmful for those with pre-existing health problems, Wilgus adds. Emergency room visits for respiratory problems such as asthma and COPD increase dramatically during wildfire smoke events, doubling in some cases. During the 2023 Canadian wildfires, when smoke spread across much of the US, emergency room visits for asthma increased nearly 20%.
Smoke exposure can also worsen other medical conditions. Emergency departments see more visits related to cardiovascular diseases after days of smoke. And a growing body of research suggests that smoke exposure is linked to long-term impacts, such as an increased risk of developing dementia.
Overall, air quality has improved in the United States over the past 20 years, says Tarik Benmarhnia, a climate and health scientist at the Scripps Institution of Oceanography at the University of California, San Diego. But wildfire smoke is erasing many of those achievements.
“Maybe like 10 years ago, wildfires were a rare problem. It was a once-in-a-lifetime thing for most people,” he says.
But climate change has increased the chances of wildfires breaking out in many parts of the country and the intensity of many of the burns and smoke they produce.
“Unfortunately, this is not the first or the last that the people of Los Angeles will experience,” Benmarhnia says.
Wondering which AQI is safe and what activities are safe in different AQIs? Life Kit explains.
The dangers of breathing wildfire smoke
Wildfires burn at extremely high temperatures, making their ash more toxic than other pollutants, such as car exhaust. But in many cases, even during these ongoing fires, It’s not just trees and organic matter that burn. Houses, cars and other materials also catch fire, adding potentially harmful particles to the pollution load.
“It’s just a toxic soup,” says Lisa Miller, a wildfire smoke expert at the University of California, Davis. “Think about all the synthetic fibers that are present in your living room: on your couch, on your carpet, on your clothes. All of those things can be particularly toxic” if they go up in smoke, he says.
Higher risks for some people
Wildfire smoke is dangerous to everyone, but it is especially dangerous to some people, including children and older adults, pregnant people, and anyone with pre-existing health problems.
First responders and firefighters are exposed to the worst of the smoke. A 2019 study found that heavy and repeated exposure to smoke among wildland firefighters is linked to increased risks of lung cancer and cardiovascular disease.
Children may be especially vulnerable, doctors say, because they breathe more air (and therefore more smoke) relative to their body size.
Pregnant people should also be careful, Miller says. There is growing evidence that exposure to wildfire smoke is linked to increased chances of premature birth and lower birth weight, an outcome that is sometimes linked to health problems later in life.
Older people and those with pre-existing health problems, such as heart problems, are also at higher risk.
The Shots blog breaks down tips on how to protect those most at risk from wildfire smoke.
How to protect yourself from wildfire smoke
“If you can smell smoke, it’s time to limit your exposure as much as possible,” Wilgus says. She says the best way to protect yourself is to leave the area and, if possible, get out of range of wildfire smoke.
If that’s not an option, he suggests staying inside with the windows tightly closed. Limit your physical activity. Use an air filter if you have one.
If you must go out, consider wearing an N95 mask, which effectively blocks smaller particles from entering your lungs if worn correctly.
No level of exposure to wildfire smoke is completely safe, Miller says. But toxicologists have a saying: “The dose makes the poison. It’s a matter of how much and for how long you are exposed.”
That means anything you can do to limit the dose, he says, will help protect you.
For more tips, check out the Life Kit guide.
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