Fine particles (PM2.5) are the main health risk from smoke
Wildfire smoke is a complex mix of gases and particles, but the dominant health hazard is fine particulate matter — particles 2.5 micrometres or...
Wildfire smoke is a complex mix of gases and particles, but the dominant health hazard is fine particulate matter — particles 2.5 micrometres or smaller, called PM2.5. These particles are too small to see, slip past the body’s natural defences, and travel deep into the lungs and bloodstream. Health Canada notes there is no known safe level of exposure to PM2.5; even low concentrations affect health, and the US CDC and EPA say the same. Between 2013 and 2018, air pollutants in wildfire smoke contributed to up to 240 deaths each year in Canada from short-term exposure and up to 2,500 deaths each year from long-term exposure. PM2.5 worsens existing asthma and chronic obstructive pulmonary disease, increases cardiovascular events, irritates eyes and throat, and triggers headaches in otherwise healthy adults. The same particles can travel thousands of kilometres on prevailing winds, which is why Canadian wildfires regularly affect air quality across the country and into the eastern United States. Reducing exposure during smoke events is therefore not a marginal precaution — it is the single most effective health intervention available to the general public.
There is no safe level of PM2.5 exposure — Health Canada attributes up to 2,500 deaths a year nationally to long-term wildfire-smoke particle exposure.
Source: Canada — Wildfire Smoke and Your Health
Last reviewed 2026-05-02.
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