The perils of wildfire smoke don't stop at the lungs or the heart. They can also affect the brain.
Recent research shows tiny particles from wildfire smoke — known as PM2.5, fine particulate matter — are so small they can travel deep into the lungs.
But they don't always end their journey there.
Some slip into the bloodstream, or get to the brain directly through the nose, says Dr. Bhavini Gohel of the University of Calgary’s O'Brien Institute for Public Health.
When toxins reach the brain, they can cause inflammation, resulting in fogginess, lack of focus and headache, she says.
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Increasing exposure to these harmful particles can also cause long-term damage to brain cells leading to cognitive decline.
Health concerns over dangerously polluted air come after drifting wildfire smoke from northern Ontario turned skies hazy in southern parts of the province.
Gohel, medical lead for the Climate Health System Alliance, says an increasing exposure to this air can lead to dementia.
“Before we were very focused on the lungs, but now we're starting to understand more and more the effects that we're seeing on the actual brain, and it really is sort of mainly cognitive.”
A study of nearly 7,000 middle-aged adults across Canada published in May found people living in areas with higher air pollution scored worse on memory tests.
Dr. Abo Akintan, medical director at multiple long-term care facilities in Toronto, says the disruption caused by the particles can affect the brain’s ability to transfer information properly.
“Thus, we see some of the cognitive changes that we see," says Akintan.
"And we know that long-term exposure over several weeks, months, years definitely does lead to dementia as well as other cognitive changes.”
Akintan says she encourages her patients to stay indoors and close windows to prevent exposure. The long-term care homes she works at have also opened cooling areas and brought in air purifiers.
For many patients, the effect is cumulative, and more common in populations where people have chronic smoke exposures.
“Usually these are people that are in lower socio-economic status areas," Akintan added.
"Certain populations that we know where they're more exposed to wildfires, we definitely see that there is a higher incidence of cognitive impairment and dementia in those populations.”
For those who can't stay indoors, the Public Health Agency of Canada has said that wearing an N95, KN95 or KF94 mask can offer some protection from wildfire smoke. Other masks, including cloth and medical or surgical masks, don't fit as snugly and the material isn't as effective at filtering out the smoke particles, it said.
Some firefighters also use tight-fitting elastomeric respirators that filter out hazardous gases and particles.
This report by The Canadian Press was first published July 17, 2026.
