Topline
The National Weather Service is cautioning people in states as far south as Virginia to monitor local air quality as smoke from hundreds of Canadian wildfires pours over the border and threatens the health of local Americans.
Wildfire smoke from northwestern Ontario fills the sky in Toronto, Canada, on July 15, 2026.
Xinhua News Agency via Getty Images
Key Facts
The National Weather Service has issued air quality alerts due to wildfire smoke in parts of Montana, Minnesota, Wisconsin, Michigan, Ohio, Illinois, Indiana, Pennsylvania, New York, Vermont, New Hampshire, Massachusetts, Connecticut, Delaware, New Jersey, Virginia, West Virginia and Washington D.C.
Air quality in parts of Michigan has been declared “hazardous”—the most extreme category—and Wisconsin and Minnesota are experiencing “very unhealthy” levels of air pollution.
New York, especially northern parts of the state, New Jersey, Massachusetts and Connecticut are warning of “unhealthy” air and a widespread haze from the smoke, and states further south and east are warning sensitive populations may be at risk.
The smoke is spilling across borders from roughly 850 wildfires burning in Canada, many of the largest in Ontario, and more than a dozen fires in northern Minnesota.
HOW TO STAY SAFE FROM WILDFIRE SMOKE
Those in states with extreme air quality warnings are being cautioned to limit outdoor activity and, in states with very unhealthy and hazardous warnings, to stay inside altogether with windows closed. Doctors advise anyone with heart or lung disease to stay indoors, and other groups to take precautions. For people who work outside, health officials have recommended wearing an N95 mask, which can filter at least 95% of airborne particles.
WHY IS WIDLFIRE SMOKE SO DANGEROUS?
Smoke from wildfires is made of water vapor, pollutants and particulate matter, which can penetrate the lungs and bloodstream, trigger systemic inflammation, exacerbate conditions like asthma and increase the risk of heart attacks and strokes. Smoke also contains a mix of harmful gases, most notably carbon monoxide. Wildfire smoke has been linked to respiratory and cardiovascular health problems, with children and teenagers, older adults, pregnant people and anyone with pre-existing heart or lung conditions at a particular risk.
SHOULD PEOPLE IN WILDFIRE SMOKE STATES WEAR A MASK?
When the Air Quality Index rises to unhealthy levels—as it has in Michigan, Wisconsin, Minnesota, Illinois, New York, New Jersey, Massachusetts and Connecticut on Thursday—masks are recommended for people who must spend time outside. Respirator masks worn correctly may provide some protection against fine particles in the smoke, but they do not help with hazardous gases. Staying inside is considered the safest option, but those who must go outside can mitigate some risk by wearing a mask. N95 or P100 respirators are considered the most effective.
Key background
Scientists say climate change is creating hotter, drier conditions and longer fire seasons, increasing the likelihood of large, intense wildfires across North America. NASA says human-caused warming is driving more frequent and severe wildfire conditions in many regions, and that extreme wildfire activity has more than doubled worldwide over the past two decades. Research shows fire seasons in some areas are now more than a month longer than they were 35 years ago, and those larger fires also produce more smoke, allowing hazardous air pollution to travel hundreds or even thousands of miles and affect millions of people far from the flames.
BIG NUMBER
$394 billion to $893 billion. That’s the annual cost of wildfires in the United States each year, according to the Joint Economic Committee, including direct and indirect deaths and injuries, health impacts from wildfire smoke, income loss, watershed pollution and other factors.