The dangers of wildfires do not end once the flames are put out, and long-term threats may continue to put thousands of people at risk.

Last year, deadly wildfires swept across Europe, destroying more than one million hectares of land, Euronews reports. This is four times more than in 2024 and corresponds to an area larger than the entire island of Corsica.

More than 1,800 wildfires were recorded, releasing over 38 million tonnes of CO₂ into the atmosphere. Deadly fires in Portugal and Spain accounted for more than two-thirds of the EU’s total damage, and according to attribution experts, their likelihood was 40 times higher due to climate change.

Researchers are now warning that even after fires are extinguished, residents returning to their homes may still be exposed to known carcinogens.

A new study published in Environmental Science & Technology Letters analyzed the aftermath of the 2025 wildfires in Los Angeles County, which destroyed more than 18,000 homes, claimed at least 31 lives, and forced around 200,000 people to evacuate.

On the second day of the fire, researchers began collecting air samples indoors and outdoors. Sampling continued after the fire, with fieldwork concluding on February 18 — 18 days after the fire had been fully extinguished.

After analyzing the samples, scientists found that levels of volatile organic compounds (VOCs) in the post-fire period were significantly higher than during active burning. Particularly high concentrations were observed in unoccupied homes within the fire zone, indicating ongoing indoor emissions from materials that had been exposed to smoke.

Exposure to VOCs such as benzene, toluene, ethylbenzene, and xylenes (BTEX) is associated with a wide range of health effects, from short-term irritation to cancer and organ damage. However, the risks depend on concentration, duration of exposure, and individual sensitivity.

According to the American Lung Association, indoor VOC concentrations can be up to ten times higher than those outdoors. VOCs are commonly found in everyday household products such as cleaning sprays, paints, and solvents.

“Some of them are carcinogenic and clearly harmful to human health,” says Yifan Zhu, professor of environmental health sciences and co-author of the study.

“What was particularly concerning in these urban fires was the potential toxicity of the resulting smoke, because VOCs are ubiquitous in residential areas; their usual sources include building materials and household products such as cooking and cleaning supplies.”

The study authors note that regular ventilation and the use of heating, ventilation, and air-conditioning (HVAC) systems with filters rated MERV 13 or higher can help reduce exposure to VOCs. Air purifiers with activated carbon filters may also be beneficial.