Wildfire smoke exposure is linked to tens of thousands of deaths in the U.S.

A thick blanket of Canadian wildfire smoke has billowed across North American cities this week, forcing evacuations in Minnesota, cancelling sporting events, reducing visibility on roads and degrading air quality to levels deemed unsafe.

Breathing in the smoke can damage the lungs as much as smoking cigarettes over the course of just a few days, according to researchers at Stanford University.

That’s because wildfire smoke often contains chemicals, metals and dangerous particle pollution known as PM2.5, that can travel through the lungs and enter the bloodstream.

But there are threats to the heart, brain and other areas of health people should be aware of, according to experts, and wildfire smoke exposure has been linked to tens of thousands of deaths.

“Extreme heat and wildfire smoke each carry major risks, especially for people with chronic health conditions including heart disease,” Dr. Manesh Patel, chief of the division of cardiology at Duke University School of Medicine, said in a Thursday statement. “The combination of the two is extremely dangerous.”

Hitting the heart

Smoke that enters the bloodstream can trigger harmful inflammation that causes heart trouble.

Wildfire smoke can raise the risk of cardiac arrest and complications related to heart disease. A 2023 study found that the risk of fatal heart attacks nearly doubled during heat waves with high levels of fine particle pollution. The risks were even greater for women and older adults, too.

The heart isn’t the only organ under threat, either.

Matters of the mind

Smoke can trigger inflammation in the brain that lasts for more than a month, University of New Mexico scientists found in 2023.

“Neuroinflammation is the seed for all sorts of bad things in the brain, including dementia, Alzheimer’s disease – the buildup of the plaques — but also alterations in neurodevelopment in early life and mood disorders throughout life,” Matthew Campen, a professor at the school and the director of the New Mexico Center for Metals in Biology, explained in a release.

Air pollution from wildfires has been associated with a higher stroke rate and more serious strokes, too, according to research from the American Academy of Neurology earlier this year.

Birth effects

For pregnant women, wildfire smoke exposure has been tied to pre-term births.

”During pregnancy there are a lot of physiological changes – for example, respiratory rate [for mothers] increases 40 percent, meaning that more smoke gets inhaled – which could affect fetal development,” Sally Picciotto, an associate researcher at the U.C. Berkeley School of Public Health, said in 2024.

Wildfire smoke exposure is expected to continue this weekend in northern states.

Detroit, Chicago, Washington, D.C.,, and New York topped the list of cities with the worst air quality in the world Friday morning, according to air quality tracker IQAir.

People can protect themselves from the smoke by staying indoors, wearing a well-fitting KN95 mask or respirator and ensuring all doors and windows are well-sealed.