Researchers at the Icahn School of Medicine at Mount Sinai have found that wildfire smoke may carry greater health risks than equivalent amounts of air pollution from other sources.

Two large-scale studies examined long-term exposure to wildfire-related fine particulate matter (PM2.5), finding stronger associations with cardiovascular and respiratory hospitalisations, as well as poorer survival among people with lung cancer.

The research, led by first author Min Zhang, PhD, and senior author Yaguang Wei, PhD, compared wildfire-related PM2.5 with pollution from non-wildfire sources.

Published in The Lancet Oncology and Nature Communications, the studies examined health outcomes across millions of people in the United States.

Together, the findings suggest that the source of air pollution may matter as much as the amount people are exposed to.

Wildfire-related PM2.5 was linked with greater health risks per unit of exposure, suggesting that wildfire smoke represents a distinct environmental health concern rather than simply another source of particulate pollution.

Wildfire smoke and lung cancer survival

The first study investigated the relationship between long-term wildfire-related PM2.5 exposure and survival among older adults diagnosed with lung cancer.

Researchers analysed data from 414,016 people aged 65 and over using the SEER-Medicare database.

Researchers estimated exposure to wildfire and non-wildfire PM2.5 based on where participants lived, using total ambient PM2.5 estimates developed by the researchers alongside wildfire-specific estimates produced by Stanford University researchers.

Both forms of PM2.5 were associated with higher mortality following a lung cancer diagnosis. However, equivalent increases in wildfire-related exposure were associated with substantially greater toxicity.

Although wildfire-related PM2.5 represented only around 4% of total PM2.5 exposure, researchers estimated that it accounted for approximately 17% of mortality associated with total PM2.5 exposure.

The analysis also found that more smoky days and longer exposure periods were associated with poorer survival. Researchers estimated that hundreds of deaths each year among the study population were attributable to wildfire-related PM2.5 exposure.

Cardiovascular and respiratory risks

The second study examined the relationship between long-term wildfire smoke exposure and hospitalisation for cardiovascular and respiratory conditions.

Researchers analysed records from residents across 20 US states between 2006 and 2019, combining hospitalisation data with models estimating long-term exposure to wildfire and non-wildfire PM2.5.

The study covered more than 57 million cardiovascular hospitalisations and almost 33 million pulmonary disease hospitalisations.

Long-term exposure to wildfire-related PM2.5 was associated with increased hospitalisation risks across a wide range of conditions.

These included heart failure, ischemic heart disease, hypertension, asthma, pneumonia, chronic obstructive pulmonary disease, and other respiratory illnesses.

At comparable concentrations, wildfire-related PM2.5 was consistently associated with larger increases in hospitalisation risk than PM2.5 from other sources.

Some communities face greater risks

The researchers also identified particularly strong associations among racial and ethnic minority populations, people living in metropolitan areas and communities with lower educational attainment and greater socioeconomic deprivation.

The findings therefore point to differences in how wildfire-related air pollution affects populations, alongside the broader health risks associated with exposure.

Wildfire smoke poses a distinct health threat

The two studies indicate that assessing exposure based solely on the overall concentration of PM2.5 may overlook differences in its health effects depending on its source.

The researchers now intend to investigate which chemical components of wildfire smoke may account for its greater toxicity.

Further work will also examine the biological mechanisms through which wildfire-related PM2.5 influences cardiovascular health, respiratory disease, and cancer outcomes.

The findings suggest that strategies addressing air pollution may need to distinguish wildfire smoke from pollution generated by other sources, particularly as exposure becomes more widespread.