It kills more people every year than car accidents, war or drugs. This invisible killer is air pollution from sources such as cars and trucks or factory smokestacks.
But as wildfires intensify and become more frequent in a warming world, smoke from those fires is emerging as a new and deadly source of pollution, health experts say. According to some estimates, wildfire smoke – which contains a mixture of dangerous air pollutants such as particulate matter, nitrogen dioxide, ozone and lead – already causes up to 675,000 premature deaths annually worldwide, as well as a range of respiratory, heart and other diseases .
Research shows wildfire smoke is beginning to erode global progress in cleaning up pollution from tailpipes and smokestacks as climate change supercharges wildfires.
“It’s heartbreaking, it really is,” said Dr. Afif El-Hasan, a pediatrician specializing in asthma care at Kaiser Permanente in Southern California and director of the board of the American Lung Association. Fires “put our homes at risk, but they also put our health at risk,” Dr. El-Hassan said, “and it’s only going to get worse.”
Those health concerns came to the fore this week as wildfires ravaged the Los Angeles area. Residents began returning to their neighborhoods, many littered with ash and rubble, to survey the damage. Air pollution levels remained high in many parts of the city, including northwest coastal Los Angeles, where the air quality index rose to “hazardous” levels.
Los Angeles, in particular, has seen air pollution at levels that could increase daily mortality by 5 to 15 percent, said Carlos F. Gould, an expert on the health effects of air pollution at the University of California, San Diego.
That means the current death tolls, “while tragic, are probably gross underestimates,” he said. People with underlying health problems, as well as the elderly and children, are particularly vulnerable.
The rapid spread of this week’s fires in densely populated neighborhoods, where they burned homes, furniture, cars, electronics and materials such as paint and plastic, made the smoke more dangerous, said Dr. Lisa Patel, a pediatrician in the San Francisco Bay Area. executive director of the Medical Society Consortium for Climate and Health.
A recent study found that even for homes that aren’t destroyed, smoke and ash billowing inside could stick to carpets, sofas and drywall, creating health hazards that can linger for months. “We are breathing in this toxic mixture of volatile organic compounds and polycyclic aromatic hydrocarbons and hexavalent chromium,” said Dr. Patel. “All these are harmful.”
Intensifying and more frequent fires, meanwhile, are upending experts’ understanding of smoke’s health effects. “Wildfire season is no longer a season,” said Colleen Reid, who researches the health effects of air pollution from wildfires at the University of Colorado Boulder. “We have fires all year round that hit the same population repeatedly.”
“The health effects are not the same as if you are exposed once and then not again for 10 years,” he said. “The effects of that are something we still don’t really know.”
A United Nations report from 2022 concluded that the risk of catastrophic fires around the world will increase in the coming decades. Warming and drying caused by climate change, along with development in places vulnerable to wildfires, were expected to intensify a “global fire crisis,” the report said. Both the frequency and intensity of extreme wildfires have more than doubled over the past two decades. In the United States, the average area burned annually has increased since the 1990s.
Now, wildfire pollution is reversing decades of air quality improvements brought about by cleaner cars and electricity generation. Since at least 2016, in nearly three-quarters of states in the continental US, wildfire smoke has eroded about 25 percent of progress in reducing concentrations of a type of particulate matter called PM 2.5, according to a study in Nature in 2023.
In California, the effect of wildfire smoke on air quality outweighs the public health gains from reducing air pollution from cars and factories, state health officials have found. (By releasing carbon dioxide and other planet-warming gases into the atmosphere, wildfires are a major contributor to climate change: Wildfires that ravaged Canada’s boreal forests in 2023 produced more greenhouse gases than burning fossil fuels in all but three countries . )
“It’s not a pretty picture,” said Dr. Gould of UC San Diego, who participated in the Nature study. If emissions of global-warming gases continue at current levels, “we have some work suggesting that US wildfire smoke mortality could increase by 50 percent,” he said.
A silver lining is that the Santa Ana winds that have so fiercely fueled the flames in recent days are blowing some of the smoke toward the ocean. This contrasts with smoke from the 2023 wildfires in Canada that drifted into New York and other US states hundreds of miles away, causing spikes in emergency room visits for asthma.
At one point that year, more than a third of Americans, from the East Coast to the Midwest, were under air quality warnings from smoke from wildfires in Canada. “We’re seeing new and worsening threats in places they’re not used to,” said pediatrician Dr. Patel.
The new normal is bringing changes to health care, Dr. Patel said. More health systems are sending air quality alerts to vulnerable patients. At the small community hospital where she works, “every child that comes in with wheezing or asthma, I talk to them about how air pollution is getting worse because of fires and climate change,” she said.
“I teach them how to look for air quality and say they should ask for an air purifier,” added Dr. She also warns that children should not be involved in cleaning up after a fire.
Scientists are still trying to understand the full range of health effects of wildfire smoke. A big question is how much of what researchers know about vehicle exhaust and other forms of air pollution applies to wildfire smoke, said Mark R. Miller, a researcher at the Center for Cardiovascular Science at the University of Edinburgh who led a recent global research climate change, air pollution and fires.
For example, exhaust particles “are so small that when we breathe them in, they go deep into our lungs, and they’re actually small enough that they can pass through our lungs into our blood,” he said. “And once they get into our blood, they can be carried around our body and start to accumulate.”
This means air pollution affects our entire body, he said. “It affects people who have diabetes, it affects the liver and the kidneys, it affects the brain, it affects pregnancy,” he said. What is not yet clear is whether pollution from wildfires has all these same effects. “But it’s possible,” he said.
Experts have a number of tips for people living in smoky areas. Monitor air quality alerts and follow evacuation orders. Stay indoors as much as possible and use air purifiers. When you go outside, wear N95 masks. Don’t do vigorous exercise in bad air. Keep children, the elderly and other vulnerable groups away from the worst of the smoke.
Ultimately, addressing climate change and reducing all types of air pollution is the way to reduce the overall health burden, said Dr. El-Hassan of the American Lung Association. “Can you imagine how much worse things would be if we hadn’t started cleaning up the emissions from our cars?” he said. “I try to think, glass half full, but it breaks my heart and worries me.”
