Here’s what the health risks are from Canadian wildfire smoke : NPR

This story is updated to reflect the current wildfire smoke conditions in the U.S. The original story was published Jan. 8, 2025.

Smoke from Canadian wildfires continued to prompt air quality alerts Monday in the Northeast U.S. as well as the Upper Midwest.

Michigan saw a statewide air quality advisory on Monday, and while Minnesota is seeing some relief, the wildfire smoke is persisting in Wisconsin, and spreading across New York, Vermont, and Maine.

Canada is experiencing its second worst wildfire season on record, according to government data. There have been nearly 4,000 fires recorded already this calendar year.

Exposure to wildfire smoke is a growing health problem across the country, as human-caused climate change increases the risk and intensity of wildfires and the smoke that can drift thousands of miles downwind from them.

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 pollution sources like ozone and fine particulates. Many scientists don’t think there’s a “safe” AQI level because the measurement doesn’t capture many harmful pollutants, but under 50 is often considered acceptable. Higher numbers indicate more health-damaging pollution in the air.

On Monday the AQI in Detroit was at least 159. On a smoky day, when AQI levels reach 100 to 200, “the exposure to the fine particulate matter, the air pollution, is similar to smoking a quarter to half a pack a day,” Wilgus says.

That exposure takes a toll on a healthy person. But it is particularly harmful for those with pre-existing health issues, Wilgus adds. Emergency room visits for respiratory issues like asthma and COPD increase dramatically during wildfire smoke events, as much as doubling in some cases. During the Canadian wildfires in 2023, when smoke wafted across much of the U.S., emergency room visits for asthma increased by nearly 20%.

Smoke exposure can also worsen other medical conditions. Emergency departments see more cardiovascular related visits after smoky days. And a growing body of research suggests smoke exposure is linked to long-term impacts such as a higher risk of developing dementia.

Overall, air quality has improved in the U.S. 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 gains.

“Just maybe like ten years ago wildfire was an exceptional issue. It was something that happens once in a lifetime for most people,” he says.

But climate change has increased the chance of wildfires across many parts of the country, and the intensity of many of the burns themselves and the smoke they produce.

“This is unfortunately not the first one and not the last one the people in Los Angeles are going to be experiencing,” Benmarhnia says.

Wondering what AQI is safe and what activities are safe at different AQIs? Life Kit explains.

The dangers of breathing wildfire smoke 

Wildfires burn at extremely high temperatures, which makes their ash more toxic than other pollution, such as car exhaust. But in many cases, including during these ongoing fires, it’s not just trees and organic matter that burn. Homes, cars and other materials go up in flames, too, 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 of all the synthetic fibers that are present in your living room – in your couch, in your carpet, in your clothes. All those things can be particularly toxic” if they go up in smoke, she says.

Higher risks for some people

Wildfire smoke is hazardous for everyone, but it’s especially dangerous for some people, including children and older adults, pregnant people and anyone with preexisting health problems.

First responders and firefighters are exposed to the worst of the smoke. A 2019 study found that heavy, repeated smoke exposure among wildland firefighters is linked with higher risks of lung cancer and cardiovascular disease.

Children can be especially vulnerable, doctors say, because they breathe in more air – and therefore more smoke – relative to their body size.

Pregnant people should also take care, says Miller. There’s growing evidence that wildfire smoke exposure is linked with higher chances of preterm birth and lower birth weights, an outcome sometimes linked with health issues later in life.

Older people and those with preexisting health problems like heart issues are also at higher risk.

The Shots Blog breaks down advice for how to protect people who are more at risk from wildfire smoke.

How to protect yourself from wildfire smoke 

“If you can smell smoke, those are times to limit your exposure as much as possible,” says Wilgus. She says the best way to protect yourself is to leave the area and get outside the range of the wildfire smoke, if possible.

If that’s not an option, she suggests staying indoors with the windows tightly shut. Limit your physical activity. Run an air filter if you have one.

If you have to go outside, consider wearing an N95 mask, which effectively blocks most tiny particles from getting into your lungs if worn correctly.

No level of exposure to wildfire smoke is completely safe, says Miller. But toxicologists have a saying, she says: “The dose makes the poison. It’s about how much, and how long, you’re exposed.”

That means everything you can do to limit the dose, she says, helps protect you.

For more tips, check out Life Kit’s guide.