Scientists at the Barcelona Institute for Global Health (ISGlobal) found that between 2004 and 2022, wildfire smoke was responsible for an average of 535 premature deaths per year across Europe. Standard calculations had placed the figure at just 38.
The discrepancy stems from a long-held assumption that PM2.5 particles—tiny, inhalable pollutants less than 2.5 microns in diameter—are equally harmful regardless of their source. The study challenges that view, showing wildfire-related particles are significantly more toxic than those generated by traffic or industry.
"Although wildfires are less frequent, the health damage caused by their particles is stronger," said Prof Cathryn Tonne, an environmental epidemiologist at ISGlobal and co-author of the study.
Rising smoke amid record-breaking fires
The research coincides with one of Europe's most destructive fire seasons on record. According to EU monitoring data, nearly 900,000 hectares of land have burned in 2025 so far, more than double the average of the past two decades for this point in the year. Fires across southern Europe and the Balkans have killed several people in recent weeks, but scientists warn the invisible health burden of smoke may be far greater.
"Smoke can travel hundreds of kilometres, exposing far more people than those directly threatened by flames," Tonne said.
Stronger risks for heart and lungs
The ISGlobal team combined daily mortality records from 32 countries with smoke exposure data over nearly two decades. Their models showed that each additional microgram of wildfire PM2.5 per cubic metre of air increased:
The risk persisted for up to a week after exposure, highlighting the delayed but deadly effects of toxic smoke.
Prof Antonio Gasparrini, an environmental epidemiologist at the London School of Hygiene & Tropical Medicine who was not involved in the study, said the findings were "deeply concerning" given the accelerating pace of climate-driven wildfires.
A growing global crisis
Air pollution is already considered one of the world's leading health threats. A global study published in December linked 1.53 million deaths annually to both short- and long-term exposure to wildfire pollution. The new ISGlobal analysis, focused only on short-term effects, suggests the true toll may be even higher than global estimates currently reflect.
Indoor exposure is also a rising concern. A separate study earlier this year found that wildfire smoke infiltrates homes housing over one billion people worldwide each year. Even with doors and windows shut, indoor air pollution on wildfire days can be nearly three times higher than usual.
Northward shift of Europe's fire belt
Europe's vulnerability is expected to grow as warming temperatures and prolonged droughts expand the traditional "fire belt" beyond the Mediterranean.
"Sooner or later, what we are seeing in Spain, Portugal and Greece will occur in central and northern Europe," warned Victor Resco de Dios, associate professor of forestry at the University of Lleida. "This is not just a Mediterranean issue—it is a European one."
With greenhouse gas emissions continuing to dry out landscapes and extend fire seasons, scientists fear the deadly legacy of smoke will become one of the most severe yet least visible public health crises of the climate emergency.