covering the surrounding regions with a dense fog laden with smoke containing harmful gases and particles that represent serious health risks. Here’s what you need to know about the risks of smoke, which will likely persist not only in Southern California, but also in other regions of the world where wildfires occur:
More toxic than normal air pollution, smoke from wildfires can linger in the air for weeks and travel hundreds of miles.
Forest fires not only burn vegetation and trees, but also cities, destroying vehicles, buildings and their contents. In addition to soil particles and biological materials, smoke from fires often contains traces of chemicals, metals, plastics and other synthetic materials.
In laboratory experiments, a given amount of wildfire smoke causes more inflammation and tissue damage than the same amount of air pollution, according to Kent Pinkerton, co-director of the Center for Health and the Environment at the University of California, Davis.
Studies have linked smoke from wildfires to higher rates of heart attacks, strokes and cardiac arrests, increases in emergency room visits for respiratory problems, and weakened immune defenses. In Maryland, a study identified an increase in heart and lung disease in 2023 associated with smoke from fires up to 2,100 miles (3,380 km) away in Canada.
Fires have also been linked to eye irritation and skin problems. The effects of exposure can persist for years. Following the Hazelwood coal mine fire in Australia in 2014, rates of heart disease remained elevated for two and a half years, and respiratory illnesses for five years, according to researchers.
Exposure to wildfires during pregnancy has been associated with pregnancy loss, low birth weight, and preterm birth. A study in California found a link between fire smoke exposure and cellular damage in first and second trimester placentas. Canadian researchers have reported that people who lived outside large cities and within 50 kilometers (31 miles) of a wildfire in the last decade had a 4.9% higher risk of lung cancer and a 10% higher risk of brain tumors. Exposure to the Camp Fire in California in 2018 was linked to changes in cognition and brain activity six to 12 months later, possibly related to stress and trauma.
Data from California also shows an increase in fungal infections in the months following smoke exposure, likely due to airborne fungal spores.
Greater exposure to wildfire smoke is also associated with higher odds of developing dementia, according to a study of older people in Southern California who did not have dementia at baseline. Even “a few days of heavy smoke,” with an Air Quality Index above 200, could translate into increased risk, said Joan Casey of the University of Washington in Seattle, who led the study.
More frequent wildfires, likely linked to climate change, mean people will be exposed more frequently, and the long-term effects of smoke exposure over multiple seasons are still unclear.
“Repeated exposure is more likely to cause illness, but it’s difficult to make predictions because you don’t know how many fires you’ll face, how long they will burn, or what the smoke will contain,” said Keith Bein of the UC Center for Health and the Environment. Davis.
Researchers are also studying the long-term effects of smoke particles on water supplies, crops or livestock; the effects of urban smoke from fires; the impact of prenatal smoke exposure on children’s neurological and respiratory development; and whether smoke from fires amplifies the adverse effects of extreme heat. Additionally, nutrients carried by smoke could contribute to algal blooms downstream, with implications for drinking water reservoirs and lake ecology, experts warn.
Experts advise limiting outdoor activities, especially strenuous sports, and wearing N95 masks when fire smoke is present. The U.S. Environmental Protection Agency offers an online course with instructions for reducing exposure to smoke outdoors and indoors.
Doug Brugge, chair of the Department of Public Health Sciences at the University of Connecticut School of Medicine, said smoke from fires can be deadly. “People should reduce their exposure, especially if they are in a vulnerable population, such as the elderly, young children, or people with respiratory illnesses.”
