Wildfire smoke can damage heart and lungs even after the blaze has subsided

Exposure to residual fine particulate matter (PM2.5) from wildfire smoke can lead to health consequences lasting up to three months afterwards, significantly longer than the few days noted in earlier research, and the exposure can take place even after the fires are extinguished.

These results were detailed in a recent study in Epidemiology published on May 28 by scientists from the Icahn School of Medicine at Mount Sinai and Harvard T.H. Chan School of Public Health.

This medium-term exposure to PM2.5 from wildfire smoke was associated with heightened risks for several cardiorespiratory conditions, including ischemic heart disease, cerebrovascular disease, arrhythmia, hypertension, pneumonia, chronic obstructive pulmonary disease, and asthma. 

“Even short exposures from minor fires lasting just a few days can result in enduring health repercussions.“

Yaguang Wei, associate, Harvard Chan School Department of Environmental Health

PM2.5 is a collection of minute particles and a significant element of wildfire smoke. When compared to non-smoke PM2.5, smoke PM2.5 is smaller and deemed more hazardous due to its higher concentration of carbonaceous compounds, which are more prone to provoke oxidative stress and inflammation, thereby posing a greater risk to public health.

The research also indicated larger impacts in areas with more greenery or greater disadvantages (e.g., lower education levels, higher unemployment, inferior housing conditions, and increased poverty), as well as among individuals who have smoked at any point in their lives.

This study is the first to investigate the medium-term health effects of wildfire smoke comprehensively. It also marks the first comprehensive assessment of its consequences for all significant types of cardiovascular and respiratory disorders.

“Wildfire incidents in the United States have significantly risen over recent decades, leading to increased emissions that have started to reverse years of air quality enhancements,” stated corresponding and lead author Yaguang Wei, assistant professor of environmental medicine at the Icahn School of Medicine and department associate in the Department of Environmental Health at Harvard Chan School. “Even brief exposures from small fires lasting only a few days can culminate in lasting health effects. There is a pressing need for research to completely understand the health ramifications of wildfire smoke to enhance awareness among the public and health professionals, as well as to aid in crafting effective regulations to mitigate these impacts.”

A total of 13,755,951 hospitalizations for cardiovascular issues and 7,990,910 for respiratory ailments were documented among residents of all ages across 15 U.S. states (Arizona, Colorado, Delaware, Georgia, Iowa, Kentucky, Michigan, Minnesota, North Carolina, New Jersey, New York, Oregon, Rhode Island, Washington, and Wisconsin). These were correlated across time and location using residential addresses to smoke PM2.5 exposures from 2006 to 2016. Among the disorders examined, hypertension exhibited the most significant increase in hospitalization risk related to smoke PM2.5 exposure. 

The team developed and utilized a novel self-controlled design within a cohort framework to simulate a quasi-experimental study. Within this cohort framework, researchers did not randomly assign participants to different levels of smoke exposure; rather, they monitored a participant’s health and smoke exposure over a defined duration, which can introduce bias from unmeasured confounders. This self-controlled design inherently addresses factors that remain constant or change slowly over time — such as genetics — even when they are not measured, as each individual is compared to themselves. This self-matching method enhances the credibility of study results. 

“Wildfires can persist for weeks to months, and smoke PM2.5 may remain airborne for extended durations, which may keep the air hazardous even after a wildfire has concluded,” noted Wei. “Current wildfire management strategies are outdated and ineffective. For instance, controlled burns can diminish wildfire risk but are primarily implemented to safeguard property instead of public health. Increased focus should be directed towards wildfire management rather than relying solely on traditional air quality measures in response to the rising wildfire activity.”

“As wildfires increasingly become more frequent and intense, and their effects on human health become clearer, addressing these health impacts is vital for public health,” remarked Rosalind Wright, dean for public health and chair of the Department of Public Health at the Icahn School of Medicine. “The public and medical professionals should take preventive actions during and post-wildfires, such as wearing masks and utilizing high efficiency particulate air (HEPA) filters, which are becoming more accessible. 

“The findings from this research highlight the importance of maintaining such preventive measures for an extended period following the cessation of fires. Collaborative initiatives across federal, state, and local levels are crucial to protect the health of communities nationwide,” added Wright, who is also the Horace W. Goldsmith Professor in Life Course Health Research in the Departments of Public Health and Environmental Medicine; co-director of the Institute for Exposomic Research; and director of ConduITS, the Clinical and Translational Science Award (CTSA) Program at Mount Sinai.

Other co-authors from Harvard Chan included Edgar Castro, Alexandra Shtein, Bryan Vu, Yuxi Liu, Adjani Peralta, and Joel Schwartz.

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This study received funding from the National Institutes of Health.