Wildfires described by firefighters and local authorities as an "apocalyptic wall of flames" have swept across much of France and Spain, forcing more than 300,000 people to flee their homes or seek shelter.
But doctors and scientists say the immediate danger from flames and smoke is only part of the threat. Mounting evidence points to serious, and potentially fatal, long-term health consequences, not just for people caught in the fires but for those hundreds of miles away.
One study found that people who inhaled higher average levels of wildfire smoke around their homes were more likely to suffer a stroke than those exposed to the lowest levels, the European Heart Journal reported earlier this year. Based on health records of almost 25 million Americans aged 65 and over, the researchers found the risk was nearly double that triggered by the same amount of pollution from traffic and industry, with wildfire smoke estimated to cause around 17,000 additional strokes a year in the United States. Even moderate levels of wildfire pollution raised the danger, not just when the air was visibly thick with smoke.
Last week, smoke from a wildfire in the Cairngorms in Scotland travelled 50 miles east to Aberdeen.
"Wildfire is often thought of as a problem for southern Europe, but that's increasingly changing," said Dr Douglas Kelley, a global fire modelling expert at the UK Centre for Ecology and Hydrology. "In 2025, the UK experienced its most extensive recorded wildfire season, with record areas burned across the country."
He said fires on heathland, moorland and peatland "can have significant impacts on air quality and public health, even when they occur far from major population centres," adding that wildfire risk is expected to increase across much of the UK, with more frequent periods of longer fire seasons and larger fires, meaning "smoke pollution is also likely to become a more important public health issue."
Harm within days
A study last year in The Lancet Planetary Health compared daily smoke levels from wildfires with death records covering 541 million people across 32 European countries. It found the risk of dying from any cause rose during the seven days after wildfire pollution increased, and that wildfire smoke appeared more harmful than standard air pollution, according to researchers from the Barcelona Institute for Global Health.
The usual method of calculating harm from air pollution assumes tiny particles are equally dangerous whether they come from traffic, industry or a wildfire. Using that method, only 38 deaths a year would have been attributed to wildfire smoke. But when the researchers accounted for evidence that fire-released particles are more harmful, the estimate rose to 535, almost 14 times higher.
Wildfire smoke is thought to damage the body quickly because burning trees and vegetation release toxic gases and fine particles known as PM2.5, less than one-thirtieth the width of a human hair, which can travel deep into the lungs. They irritate lung tissue, causing the immune system to release inflammatory chemicals that can swell and tighten airways and increase mucus production, leading to coughing, wheezing, breathlessness and chest tightness.
The inflammation can spread throughout the body, damaging the lining of blood vessels, making them stiffer and causing blood to clot more readily, potentially raising the risk of a heart attack. It may also cause fatty deposits inside arteries to rupture, and if a resulting clot blocks blood supply to the brain, it causes a stroke.
Another study, published in the Journal of the American College of Cardiology in February, looked at 65.2 million Americans aged 65 and over and their average three-year exposure to wildfire pollution. It found those who breathed in moderate amounts had a 4 per cent greater risk of hospital admission for cardiovascular problems than those with the least exposure. At higher exposure levels, the risk of heart failure was at least 20 per cent greater.
Associate Professor Kai Chen, an environmental-health epidemiologist at the Yale School of Public Health who led the study, said wildfire smoke "contains a greater share of much smaller, chemically reactive particles than typical urban pollution."
The smallest particles may pass from the lungs into the bloodstream, where they can irritate and damage blood vessels and intensify inflammation, triggering chemical stress signals that travel around the body. These signals can disturb the nerves that keep the heart beating steadily, making its electrical rhythm unstable and causing arrhythmia. They also cause blood vessels to tighten, forcing the heart to work harder and raising the risk of a heart attack, particularly in people whose arteries are already narrowed.
For people with asthma or chronic obstructive pulmonary disease, which affects around 1.2 million people in the UK, the consequences can be more serious. Dr Matt Swallow, clinical lead at the charity Asthma + Lung UK, said people with asthma or COPD already have sensitive or damaged airways, and that smoke can trigger airway inflammation, worsening symptoms and increasing the risk of an asthma attack or COPD flare-up.
Smoke travels far
Experts warn that people do not need to be close to a wildfire to suffer effects. Powerful fires can propel smoke several miles into the sky, where faster winds may carry it across countries or oceans, and changes in weather can then bring the pollution back down into the air people breathe.
"Distance alone is often a poor indicator of exposure," said Dr Mark Parrington, a senior scientist at the EU's Copernicus Atmosphere Monitoring Service. "People do not need to be immediately downwind of a wildfire to experience wildfire smoke pollution."
In 2023, pollution from Canadian wildfires crossed the Atlantic and reached Europe. A study published in Nature last year estimated that almost 48 million Europeans experienced at least one day when particle pollution exceeded the World Health Organisation's recommended daily limit of 15 micrograms per cubic metre of air, with Canadian wildfire smoke responsible for at least half of it. The same fires sent smoke hundreds of miles across the US, and the Centers for Disease Control and Prevention found that emergency room visits for asthma were 17 per cent higher than expected during 19 days when smoke pushed air pollution to unhealthy levels.
Dr Parrington said smoke from the current French and Spanish fires is being carried mainly eastwards and is not expected to reach Britain, but he still fears Britain "may increasingly experience episodes of degraded air quality originating from fires hundreds or even thousands of kilometres away." He added: "These fires can have significant impacts on air quality and public health, even when they occur far from major population centres."
How to keep yourself safe
If you can see or smell wildfire smoke, or local authorities issue an air-quality warning, remain inside where possible and shut windows and doors.
- Switch off air-conditioning systems that draw air in from outside
- Avoid spending too long outdoors, or doing strenuous exercise outside, if there are wildfires nearby
- If driving through smoke, close windows, shut all air vents and switch the air conditioning to recirculate
- Keep inhalers close if you have asthma or other lung conditions
- If you must go outside, wear a close-fitting FFP2 or N95 mask, which will filter some of the particles
