As wildfires continue to burn larger portions of the Northern Hemisphere due to rising global temperatures, the smoke they produce is taking a devastating toll on human health — killing tens of thousands of people annually, according to multiple medical studies.
The damage begins almost immediately. Within hours of smoke exposure, asthma cases spike and ambulance calls increase. Within a day or so, emergency rooms become overwhelmed with patients suffering heart attacks, cardiovascular problems, lung issues, and mental health crises, doctors and scientists told the Associated Press.
Pregnant women face additional dangers, with smoke exposure raising the likelihood of premature births and underweight babies who may struggle with breathing problems throughout their lives. Researchers have also identified long-term connections between prolonged smoke and air pollution exposure and certain cancers, as well as dementia.
Following massive wildfires in 2018 and 2019, the medical and scientific communities began studying the health effects of smoke more closely. “More and more studies coming out finding that there’s all types of impacts that may not have been so obvious before,” said Dr. Mary Johnson, an environmental health scientist at Harvard School of Public Health.
Smoke triggers the body’s immune system into overdrive, causing widespread inflammation. Scientists have found it can damage the brain, the skin, and men’s sperm — leaving almost no part of the body unaffected, Johnson said. She added that people over 60 face an increased risk of stroke when exposed to wildfire smoke.
“Wildfire smoke is the toxic product of combustion of whatever burned,” which can include homes and vehicles, explained Dr. Courtney Howard, an emergency room physician, chair of the Global Climate and Health Alliance, and president-elect of the Canadian Medical Association. “So really it’s a big giant toxic soup of particles and gases.”
Researchers have identified at least 1,000 toxic substances in wildfire smoke, according to Luke Montrose, an environmental toxicologist at Colorado State University.
“If I gave you a list, you would recognize some of these as being very bad, oftentimes associated with the burning of diesel fuel or cigarette smoke, things like formaldehyde or volatile organic compounds,” Montrose said. “So just the smoke itself can be bad.”
So far this year, wildfires have burned more than 5,740 square miles — more than 14,860 square kilometers — across the United States. That figure is 31% above the 10-year average for this point in the year, according to the National Interagency Fire Center. When averaged over a decade, the amount of U.S. land burned each year in the 2020s is now more than double what it was 30 years ago.
Europe recorded a high amount of land burned in 2025, Canada has experienced several record or near-record fire years in the 2020s, and the Arctic has seen unprecedented levels of burning in recent years.
“Wildfires are becoming more frequent and intense because of climate change, and when a fire happens, you have smoke,” said Colleen Reid, a geographic health professor at the University of Colorado.
While larger smoke particles tend to settle near the source of a fire, the smallest particles — which scientists say cause the most harm — can travel great distances. In a typical wildfire, the most dangerous particles measure roughly one micron in size, Reid said.
Those tiny particles must first get past the body’s natural defenses, such as nose hairs and mucus. Once they reach the lungs, they can enter the bloodstream. Montrose explained that these particles are often coated in chemicals and have large surface areas, prompting the body’s defense system to “send signals to other cells that say, ‘We have a problem. We need to mount an immune response to this.’ And that’s where you get your acute effect or your effect within minutes, hours or even that day.” The impact is felt most strongly in the heart and lungs, he said.
The death toll is significant. A study published this year in the journal Science Advances found that an average of 24,100 people in the Lower 48 states died each year between 2006 and 2020 due to long-term exposure to tiny wildfire smoke particles. A separate Stanford study projects that wildfire smoke deaths in the U.S. will rise with climate change, potentially reaching an annual economic cost of $244 billion by the middle of this century.
Globally, wildfire smoke particles are responsible for 677,745 deaths each year, with nearly 39% of those victims being children under the age of 5, according to a 2021 study that used observations, health response data, and computer modeling to calculate the total.
Beyond the deadly effects, wildfire smoke also causes widespread breathing difficulties — particularly for people with asthma. A 2014 study conducted after roughly two and a half months of intermittent smoke exposure found a full doubling of emergency department visits for asthma and about a 50% increase in pneumonia cases, Howard said from Yellowknife, Canada. She noted that the subarctic region is warming at triple the global rate, making it “kind of canaries in the coal mine of the health impacts of climate change.”
“Even in individuals that don’t have asthma, the air can be so irritating that you could have difficulty with your respiratory system regardless,” Johnson said, “whether it’s coughing, whether it’s chest tightness, whether it’s sore throat, headache.”
Studies have also connected smoke exposure to impaired decision-making and other cognitive problems. Howard noted that patients arrive at the emergency room feeling depressed during heavy smoke events. She recommends seeking out clean-air spaces — such as designated shelters or libraries — to get relief from the smoke and possibly get some exercise.
Experts advise wearing high-quality masks when going outside, even though they don’t offer complete protection. Indoors, they recommend checking windows and doors for proper seals, investing in a good ventilation system, and regularly checking air filters.
“Staying away from the smoke is No. 1 if you can,” Johnson said.
