As wildfires rage across North America, new study says smoke is 14 times more lethal than earlier estimates

As North America battles one of its most destructive wildfire seasons, with more than 40,000 blazes scorching nearly 3 million acres in the US and over 5.5 million acres in Canada as of July 2025, a new study warns that the health toll of wildfire smoke is far deadlier than previously believed.

Researchers now say short-term exposure to smoke-related fine particles is linked to 14 times more deaths than past estimates suggested.

According to the study, the health risks of wildfire smoke were underestimated by nearly 93 percent. Published in The Lancet Planetary Health by researchers from the Barcelona Institute for Global Health (ISGlobal), the findings suggest exposure to wildfire smoke is responsible for an average of 535 deaths annually.


In California alone, 5,362 wildfires have resulted in 31 fatalities this year as per the CalFire data.

Why wildfire smoke is so lethal

The study examined wildfire pollutants, particularly fine particulate matter (PM2.5), microscopic particles small enough to penetrate the lungs and bloodstream deeply.

• For every 1 µg/m³ rise in PM2.5, all-cause mortality increased by 0.7 per cent, respiratory mortality by 1 per cent, and cardiovascular mortality by 0.9 per cent.
  
  
• Researchers found wildfire-generated PM2.5 is more harmful than traffic-related pollutants, intensifying risks of respiratory and heart diseases.
  
  

“These estimates were made using specific data on how wildfire smoke affects health, allowing for a more precise calculation compared to general air pollution data,” the authors noted.

How the study was conducted

The team relied on data from the EARLY-ADAPT project, covering 654 regions across 32 European countries and a population of 541 million people between 2004 and 2022.

• They combined daily mortality records with fire-related and non-fire-related PM2.5 levels.
  
  
• By broadening the timeline to include deaths occurring within seven days of exposure, the study captured wildfire smoke's delayed but deadly effects.
  
  

Previous estimates were dangerously low

The study found that short-term exposure to wildfire smoke particles (PM2.5) caused an average of 535 deaths each year, including 31 from respiratory diseases and 184 from cardiovascular causes.

Earlier methods that treated wildfire smoke the same as other fine particles had suggested only 38 deaths per year, a massive undercount.

By applying risk data specific to wildfire smoke, researchers discovered that the actual toll is nearly 14 times higher, meaning previous estimates underestimated the danger by 93 percent.

A climate-linked threat to global health

As the climate crisis fuels longer fire seasons and more intense blazes, exposure to wildfire smoke is expected to rise dramatically.

“The rising frequency and intensity of wildfires makes improving estimates of PM2.5-related wildfire mortality imperative to better track this climate change-related threat,” said Anna Alari, ISGlobal researcher and study co-author.