Wildfire Smoke and Respiratory Health: What the Science Says

Wildfire season is getting longer, and its reach is growing. In summer 2025, Canada recorded 470 uncontrolled fires burning nearly 7.3 million hectares across Manitoba and Alberta, the second-worst season on record. In southern France, a fire near Marseille on 8 July destroyed 750 hectares. In early August, a blaze near Ribaute in the Aude department ravaged 16,000 hectares. In Spain and Portugal, simultaneous fires drove air quality in several cities to levels comparable to the most polluted urban centers in China and India.

The danger doesn't stop at the fire line. Wildfire smoke can travel thousands of miles, degrading air quality in cities far removed from the flames. During the 2025 Canadian fires, Montreal temporarily ranked as the worst city in the world for air quality. Chicago recorded a severe pollution episode weeks after the fires were brought under control.

This article draws on field measurements taken during the 2025 fire season and recent peer-reviewed research to explain what wildfire smoke does to the body, and what actually works to protect indoor air.

The Impact of Wildfires on Air Quality and Health

A Significant Deterioration in Air Quality

As wildfires become increasingly frequent, it is essential to examine their effects on respiratory health. Indeed, wildfires have a highly detrimental impact on air quality.

Using professional outdoor air quality monitoring tools, TEQOYA teams analyzed extensive data from the summer 2025 wildfires and identified a substantial increase in fine particulate matter levels coinciding with the outbreak of wildfires.

The following graphs illustrate the evolution of air quality over two months, July and August 2025, in European regions affected by major wildfires. They compare typical fine particle concentrations with those recorded during these wildfire events.

In August 2025, numerous simultaneous wildfires broke out across the Iberian Peninsula, notably in Riaño, Plasencia, and Ourense in Spain, as well as Arganil in Portugal.

As shown in the graphs below, these locations experienced an exponential increase in airborne fine particles on the same day or in the days following the start of the fires. Measured values approached those observed during pollution peaks in major Chinese and Indian cities.

In France, for example, during the wildfire that broke out in Les Pennes-Mirabeau near Marseille on July 8, 2025, the regional air quality agency (ATMO-SUD) reported that air quality had never been worse in the region than during this major event. The graph below shows significant fine particle peaks in the days following the outbreak.

Beyond the threat they pose to people and property near the fire front, exposure to wildfire smoke extends far beyond the immediate vicinity. Smoke can affect populations hundreds or even thousands of kilometers away⁷, as particles released by these fires are capable of traveling extremely long distances.

The Canadian wildfires of 2025 provide a striking example. The map below shows both a sharp increase in particle concentrations near the fire zones, particularly around Calgary, Candle Lake, and Winnipeg, and a clear deterioration in air quality in cities located thousands of kilometers away, such as Montreal and Chicago. In August 2025, Chicago experienced a severe air pollution episode caused by lingering smoke from Canadian wildfires even after they had been brought under control. Montreal, meanwhile, set a global record by becoming the city with the worst air quality during the summer of 2025, with pollution peaks comparable to those of the world's most polluted metropolitan areas.

The situation in Ribaute, France, also highlights the volatility of these particles. Although the wildfire began on August 5 in the area, easterly winds initially spared the town by carrying fine particles offshore. However, a fine particle peak was recorded on August 8 as the wind subsided. Measured levels then far exceeded the region’s usual thresholds.

PM2.5 from wildfires: more toxic than other sources

Wildfire smoke is a complex mixture: fine particles (PM2.5, around 80% of suspended particles in affected areas), carbon monoxide, nitrogen dioxide, semi-volatile compounds, and heavy metals⁶. It is the PM2.5 fraction that carries the greatest health burden.

What makes wildfire PM2.5 particularly dangerous is both its size and its chemistry. Below 2.5 micrometers, these particles bypass the upper airways, reach the alveoli, and can enter the bloodstream. Epidemiological research shows that a 10 µg/m³ increase in wildfire PM2.5 raises respiratory hospitalizations by 1.3% to 10%, compared to 0.67%-1.3% for equivalent increases from other pollution sources⁷.

The WHO recommends an annual average PM2.5 level below 5 µg/m³. During wildfire episodes, this threshold is exceeded by orders of magnitude.

Health effects: symptoms and vulnerable populations

Short-term exposure to wildfire smoke causes eye and throat irritation, coughing, shortness of breath, and nasal discharge. In cases of prolonged or intense exposure, the risks extend to acute and chronic disease, including asthma exacerbation, cardiac events, and increased mortality.

The European Climate and Health Observatory estimates that wildfires caused more than 1,400 premature deaths in Europe in 2005. Studies have documented a 20-fold increase in respiratory illnesses following fires near Vilnius, Lithuania, in 2022, and a strong correlation between wildfire frequency and pneumonia rates in Portugal⁸.

The U.S. EPA identifies the following as most at risk: children, older adults, pregnant women, and people with pre-existing asthma, COPD, or cardiovascular disease⁹. This is not a marginal population. In the United States alone, more than 25 million people have asthma.

Conclusion

Wildfire smoke is no longer a regional risk confined to fire-prone areas. With climate change, it has become a global air quality issue that reaches cities thousands of miles from the nearest flame. The health data are unambiguous: wildfire PM2.5 is more toxic than other particulate sources, and indoor concentrations during fire events far exceed safe thresholds even in sealed buildings. Sheltering indoors remains the right first step. Complementing it with an air purifier proven to capture PM2.5 is the logical next one.