What you need to know about danger of wildfire smoke

Massive wildfires are raging around the world during unprecedented heat waves, blanketing millions of people under pungent haze caused by smoke carrying noxious gases and particulate matter that pose serious health risks.

Here is what you need to know about the risks of wildfire smoke.

More toxic than normal air pollution, wildfire smoke can linger in the air for weeks and travel thousands of miles.

Wildfires can burn not only vegetation but also vehicles and buildings as well as their contents. Along with particles of soil and biological ⁠materials, wildfire smoke often contains traces of chemicals, metals, plastics and other ⁠synthetic materials.

Health effects

In laboratory experiments, wildfire smoke causes more inflammation and tissue damage than air pollution, said Kent Pinkerton, co-director of the Center for Health and the Environment at the University of California, Davis. Studies have linked wildfire smoke with higher rates of heart attacks, strokes and cardiac arrests, increases in emergency room visits for asthma, weakened immune defenses and poorer survival rates after surgery. A 2023 study ⁠in Maryland identified a spike in heart and lung illnesses that was associated with wildfire smoke originating up to 2,100 miles (3,380 kilometers) away.

Wildfires also have been linked with eye and skin problems. Wildfire exposure in pregnancy has been associated with miscarriage, low birth weight and preterm delivery. A California study found a link between wildfire exposure and cellular damage in first- and second-trimester placentas. A separate study found wildfire smoke exposure during the third trimester may raise the risk of an autism diagnosis. The effects of exposure can persist for years. After Australia’s 2014 Hazelwood Coal Mine fire, heart disease rates remained elevated for two-and-a-half years and respiratory illnesses for five years. A 2026 U.S. study linked wildfire smoke exposure with elevated risks for lung, colorectal, breast, bladder and blood cancer, with the risks increasing along with the level of pollution from the fires. Exposure to the 2018 Camp Fire in California was linked to changes in cognition and brain activity six to 12 months later, California researchers found. Several studies have now linked longer-term wildfire smoke exposure to higher risks for dementia. Data from California also show an increase in fungal infections in the months following wildfire smoke exposure, likely due to spores ⁠in ⁠the smoke.

“The bad news is, there’s no safe level” of inhaled particles from wildfire smoke, said Doug Brugge, who chairs the Department of Public Health Sciences at the University of Connecticut School of Medicine. “The higher the exposure, the worse the risks, but even at levels below the national safety standards, these particles can make people sick.”

Any amount of inhaled particles will trigger inflammatory responses in the body. Children, the elderly and people with chronic illnesses are most vulnerable.

Even in healthy adults, some effects of exposure – such as sore throats, excessive phlegm, coughing, headaches and brain fog – can appear immediately and persist long after the smoke plume is gone, said Keith Bein of the Air Quality Research Center at the University of California, Davis.

Experts advise wearing N95 masks when wildfire smoke is present and limiting outdoor activities, especially strenuous sports. The longer you are outside and the harder you breathe, the more ⁠pollution you inhale, said Dr. Jasvinder Singh, a lung medicine specialist at MedStar Franklin Square Medical Center in Baltimore.

Experts also recommend the use of indoor air purifiers that can trap particles smaller than 2.5 microns. “Air purifiers reduce exposure and in our studies reduced blood pressure and cognitive impacts of air pollution,” Brugge said. For those who cannot afford an air purifier, UC Davis offers simple instructions for building one. Online instructions for reducing exposure to wildfire smoke are available from the U.S. Environmental Protection Agency (EPA).

Safety indoors

Particulates from wildfire smoke enter most buildings in high concentrations, experts say.

On average, the concentration of wildfire pollutants indoors is about half of what it is outdoors, Singh said.

If a building is poorly sealed, the concentration may be up to 70% of what it is outside, he said. Old buildings may expose people to greater amounts of pollution through drafty windows and ⁠doors. The EPA advises that ‌during wildfire smoke ‌events, people avoid indoor activities that put more fine particles into the air, such as smoking cigarettes, frying or ⁠broiling food, burning candles or incense and vacuuming without a HEPA filter.

Bein compared indoor wildfire smoke exposure ‌to second-hand tobacco smoke exposure.

“The particles … end up everywhere – on your clothes, on your walls, on surfaces and they’re still outgassing” – being released into the air – “after the smoke plume is gone,” he said.

More frequent wildfires likely linked to climate change mean people will be ⁠exposed more often. The health effects over multiple seasons are not yet clear.

“It is hard to make predictions because it ⁠is hard to say how many fires people will be exposed to, how long the fires will burn, or what the smoke will contain,” Bein said.

Researchers are ⁠looking into the long-term effects of smoke particles in water supplies, on crops or ingested by livestock; of urban wildfire smoke; of wildfire exposure in utero; and whether wildfire smoke amplifies the adverse effects of extremely hot weather. Nutrients carried in wildfire smoke may contribute to downwind algal blooms, which have implications for drinking water reservoirs and lake ecology, researchers warn.

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