Wildfire smoke is a major health threat far beyond the fire zone. A 2024 Lancet study found that landscape-fire fumes kill about 1.5 million people worldwide each year—more than floods, flames, storms and heat combined.
The smoke contains toxic gases and fine particles that inflame the airways, penetrate deep into the lungs and can enter the bloodstream. Doctors in Toronto reported more patients with allergies and shortness of breath during a recent episode, while millions of people across North America were exposed to very unhealthy pollution levels.
At a glance:
- A Nature study found that smoke from Canada’s 2023 wildfires contributed to 82,000 early deaths.
- At least 36 million people across North America were exposed to PM2.5 concentrations above 125.5 μg/m³ on 16 July, according to preliminary analysis conducted for the Guardian.
- Wildfire smoke can be more harmful than pollution from vehicles or factories because it contains more inflammatory organic compounds and ultrafine particles.
- Experts recommend checking air-quality readings, closing windows, wearing masks and moving activities indoors when pollution is high.
How smoke harms the body
Wildfire smoke is not simply ordinary air pollution. Compared with particles from factories or cars, it contains a greater share of organic compounds that increase inflammation and a higher concentration of ultrafine particles capable of reaching the deepest parts of the lungs.
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A 2021 Nature Communications study found that wildfire PM2.5 can be up to 10 times more harmful in the short term than other PM2.5. Researchers say intense peaks may overwhelm the body’s defences, while longer-term exposure is linked to much of the overall mortality burden.
Why distance and wind matter
Smoke can kill people far from the flames. The 2023 Canadian fires sent plumes into the United States and Europe; the Nature study estimated 82,000 early deaths, with about one-third of the mortality burden in the US and another quarter in Europe.
The effects depend partly on where winds carry the pollution, not only on how large a fire becomes. On 16 July, at least 36 million people across North America breathed air with very unhealthy PM2.5 concentrations above 125.5 μg/m³. In west Duluth, Minnesota, 12,000 people were exposed to an average of 541 μg/m³.
What people can do during a smoke episode
Experts recommend checking air-quality monitors in the morning, closing windows, wearing masks and moving activities indoors when pollution is too high. They also advise checking in on vulnerable neighbours, particularly older people with chronic disease who live alone.
Smoke and heat can create conflicting risks. Keeping windows closed may protect indoor air but can be dangerous without air conditioning during extreme heat, according to a BC Lung Foundation report. The source therefore describes indoor cooling and clean-air measures as a combined challenge rather than a single solution.
Questions readers ask
Who may be most vulnerable to wildfire smoke?
The source specifically highlights older people with chronic disease who live alone as vulnerable neighbours to check on. It also describes symptoms including allergies, shortness of breath and headaches during severe exposure.
Can wildfire smoke affect people outside the immediate fire area?
Yes. Smoke plumes can travel across national borders. Smoke from Canada’s 2023 fires contributed to deaths in the US and Europe, and recent pollution affected major North American population centres.
Should people stay indoors when smoke is heavy?
Experts recommend moving activities indoors, closing windows and checking air-quality readings. During hot weather, however, closed windows without air conditioning can create a separate danger, so heat and smoke must be considered together.
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