As Forest Fires Continue to Burn Across Canada, Here Are the Top Health Risks From Wildfire Smoke


Smoke from wildfires burning in Canada contain a host of noxious gases and particulate matter that carry serious health risks. Photo: Steve Russell/Toronto Star/Getty Images

Forest fires continued to burn across Canada on Thursday as the country endured its worst-ever start to wildfire season, forcing thousands of people from their homes and sending a smoky haze billowing across U.S. cities.

About 3.8 million hectares (9.4 million acres) have already burned, roughly 15 times the 10-year average, according to federal Minister of Emergency Preparedness Bill Blair. Warm, dry conditions were expected to persist in the months ahead.

Although wildfires are common in Canada, it is unusual for blazes to be burning simultaneously in the east and west, stretching firefighting resources and forcing the Canadian government to send in the military to help. Hundreds of U.S. firefighters arrived in Canada to help and more were on their way.

Prime Minister Justin Trudeau blamed climate change. “These fires are affecting everyday routines, lives and livelihoods, and our air quality,” Trudeau said on Twitter.


Some of the worst fires have sprung up in the eastern province of Quebec, and more than 11,000 people had to evacuate their homes in Quebec.

Wildfire season started unseasonably early in Alberta last month and burned a record area, and Nova Scotia continues to battle its largest-ever blaze,

In parts of the Pacific province of British Columbia, which is facing the second-biggest wildfire on record, temperatures were forecast to hit 33 Celsius (91 Fahrenheit) on Thursday, before thunderstorms and heavy rains arrive on Friday.

Rob Schweitzer, executive director of BC Wildfire, said lightning strikes could spark more blazes in tinder-dry forests and the outcome would depend on how much precipitation comes with the storms.

“When you get 150 or 200 strikes in one day from lightning coming through the province, it’s impossible to have enough resources to suppress them all,” he said.

Wildfires have eased in Alberta, the center of Canada’s oil and gas industry, but more than 3,000 people remain under evacuation orders and heat warnings are in effect in the south of the province.

Smoke-forecasting website BlueSky Canada showed wildfire smoke spreading across much of the country on Thursday. The smoke is set to intensify in Ottawa, Toronto, Cleveland and Pittsburgh and remain thick in other cities along the east coast of the United States, including New York.

(Reporting by Nia Williams in British Columbia; Editing by Cynthia Osterman)


People ride bicycles on 6th Avenue as haze and smoke caused by wildfires in Canada blanket New York City, where air quality risks were among the worst in the world on Tuesday and Wednesday. Photo: Andrew Kelly/Reuters


Health Risks

What Is Contained in Wildfire Smoke?

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

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


What Are the Known Health Effects?

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 (UC), Davis.

Studies in people have linked wildfire smoke with higher rates of heart attacks, strokes, and cardiac arrests, increases in emergency room visits for respiratory conditions, and weakened immune defenses. Wildfires have also been linked with eye irritation and skin problems.

The effects of exposure can persist for years. After Australia’s 2014 Hazelwood Coal Mine fire, rates of heart disease remained elevated for two and a half years and respiratory illnesses for five years, researchers reported in April.

Wildfire exposure in pregnancy has been associated with pregnancy loss, low birth weight, and preterm delivery. A study from California that has yet to be peer reviewed found a link between wildfire exposure and cellular damage in first- and second-trimester placentas.

Canadian researchers have reported that people who lived outside of major cities and within 50 kilometers (31 miles) of a wildfire in the past decade had a 4.9% higher risk of lung cancer and a 10% higher risk of brain tumors compared to people not exposed to wildfire.

Exposure to the 2018 Camp Fire in California was linked to changes in cognition and brain activity six to 12 months later, possibly related to stress and trauma, according to California researchers.

New data from California also show an increase in fungal infections in the months following wildfire smoke exposure, likely due to fungal spores in the smoke.


What Is Unknown?

More frequent wildfires likely linked to climate change mean people will be exposed more often. But the health effects of wildfire smoke exposure over multiple seasons are not yet clear.

“Repeated exposure, summer after summer after summer, is more likely to cause diseases, but 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,” said Keith Bein of the Center for Health and Environment at UC Davis.

Current research is also looking into the long-term effects of smoke particles in water supplies, on crops or ingested by livestock; the long-term effects of urban wildfire smoke; the effects of wildfire exposure in utero on children’s neurological development and respiratory outcomes; and whether wildfire smoke amplifies the adverse effects of extremely hot weather.

Nutrients carried in wildfire smoke may contribute to downwind algal blooms, which has implications for drinking water reservoirs and lake ecology, researchers warned earlier this year.


What Can Help Mitigate the Risks?

Experts say it is best to limit outdoor activities, especially strenuous sports, and to wear N95 masks.

An online course with instructions for reducing outdoor and indoor exposure to wildfire smoke is available from the U.S. Environmental Protection Agency.


Do We Really Need to Worry?

Doug Brugge, who chairs the Department of Public Health Sciences at UConn School of Medicine, said wildfire smoke 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 diseases.”