Choking smoke spewed by wildfires is far more dangerous than previously thought, a new study has found, with death tolls from short-term exposure to fine particulates underestimated by 93%.

Researchers found that 535 people in Europe died on average each year between 2004 and 2022 as a result of breathing in the tiny toxic particles known as PM2.5 that are released when wildfires rage.

Under standard methods, which assume PM2.5 from wildfires is as deadly as from other sources, such as traffic, they would have expected just 38 deaths a year.

The study comes as wildfires ravage southern Europe, and new data from EU fire monitors shows that 895,000 hectares (2.2m acres) have burned so far in 2025, breaking records for this time of year. They have pumped out more than twice the amount of PM2.5 that wildfires have generated on average by this point in the year over the last two decades.

“Previously, people assumed the same toxicity for wildfire particles and all particles,” said Prof Cathryn Tonne, an environmental epidemiologist at the Barcelona Institute for Global Health (ISGlobal) and co-author of the study.

“Our paper shows evidence that – although it happens less often – the health impact for the same amount of particles is stronger for wildfire particles,” she added.

Dirty air is one of the biggest threats to human health, and research suggests wildfires are a significant contributor to the vast death toll. In December, a study attributed 1.53 million deaths around the world each year to short-term and long-term exposure to air pollution from wildfires.