Wildfire smoke may harm the heart and lungs more than the same amount of pollution from traffic, industry, and other everyday sources, according to two large studies released this week by researchers at the Icahn School of Medicine at Mount Sinai in New York.
The studies found that long-term exposure to fine particles from wildfires, known as PM2.5, was associated with higher risks of hospitalization for heart failure, asthma, pneumonia, chronic obstructive pulmonary disease (COPD), and other conditions. A second analysis linked long-term smoke exposure with poorer survival among older adults with lung cancer.
The findings matter well beyond the West. Smoke from Canadian fires turned skies orange over Chicago and New York City this July, MedicalDaily reported. That means many households with older parents, young children, or relatives living with heart and lung disease may face exposures they never planned for.
The Source of Pollution Matters, Not Just the Amount
In one study, published Sept. 17 in Nature Communications, researchers analyzed hospitalization records from 20 U.S. states between 2006 and 2019. The data included more than 57 million cardiovascular hospitalizations and nearly 33 million pulmonary disease hospitalizations, according to Mount Sinai's announcement.
At equal concentrations, wildfire-related PM2.5 was consistently associated with larger increases in hospitalization risk than PM2.5 from other sources. The associations were especially strong among racial and ethnic minority groups, residents of metropolitan areas, and people in communities with lower educational attainment and greater economic hardship.
"Wildfire smoke is no longer a regional environmental issue. It is becoming a nationwide public health challenge," said Dr. Yaguang Wei, an assistant professor of environmental medicine at Mount Sinai and senior author of both studies.
Dr. Min Zhang, a postdoctoral fellow and first author of both studies, said the research found that wildfire smoke can affect both the lungs and the cardiovascular system, and that its effects may be stronger than those of similar amounts of pollution from traffic and industry.
Older Lung Cancer Patients Showed Poorer Survival
The other study, published Sept. 15 in The Lancet Oncology, followed 414,016 adults aged 65 and older with lung cancer using the SEER-Medicare database. Researchers estimated each patient's smoke exposure based on where they lived.
Wildfire-related PM2.5 made up only about 4% of total fine particle pollution but accounted for about 17% of the deaths tied to total PM2.5 exposure. More smoky days and longer periods of smoke exposure were associated with worse survival.
"Patients with lung cancer are already medically vulnerable, and our findings suggest that wildfire smoke may place them at even greater risk," Zhang said.
Christine Ekenga, PhD, MPH, of Emory University's Rollins School of Public Health, a co-author, said long-term smoke exposure may add "another, potentially preventable risk" for these patients.
MedicalDaily Evidence Check: Both studies are observational analyses of large health databases. They show associations, not proof that smoke directly caused each hospitalization or death. Exposure was estimated from where people lived rather than measured for each person. The findings have not changed federal air quality standards, but they add weight to existing advice for vulnerable groups during smoke events.
Earlier Research Points in the Same Direction
A study by Stony Brook University and Mount Sinai researchers examined the June 2023 Canadian smoke event using data from Stony Brook Hospital on Long Island. During the event, the hospital saw higher rates of visits for cardiovascular disease and high blood pressure, driven mainly by emergency department visits, along with more inpatient admissions for respiratory disease, according to the Stony Brook study summary.
A 2025 study by Mount Sinai and Harvard researchers, published in the journal Epidemiology, found that lingering smoke particles were linked to heart and lung hospitalization risks for up to three months, even after fires ended, as the Harvard Gazette reported. That work also found larger effects in more disadvantaged neighborhoods.
Taken together, the research suggests that people living far from any fire can still face meaningful risk, particularly those with chronic heart or lung conditions.
Protecting Vulnerable Relatives During Smoke Events
The people most likely to be affected include older adults, people with heart disease, asthma, or COPD, cancer patients and survivors, pregnant people, and young children. Outdoor workers and households without air conditioning or air filtration also face higher exposure.
"For people with lung cancer or chronic heart and lung diseases, monitoring air quality and limiting exposure during smoke events may be especially important," Wei said.
Practical steps include checking the daily Air Quality Index, staying indoors with windows closed when smoke is heavy, using a HEPA air purifier if available, and wearing a well-fitted N95 respirator when going outside cannot be avoided. Cloth masks offer little protection against fine smoke particles. Mount Sinai public health leaders have also advised continuing these precautions for a period after fires end.
Symptoms that can follow smoke exposure include coughing, wheezing, burning eyes, headache, and fatigue. Chest pain, severe shortness of breath, confusion, or signs of a heart attack or stroke require emergency care. People with chronic conditions can ask their clinician for a smoke-day plan that covers medications, rescue inhalers, and when to seek help.
Air purifiers and N95 masks cost money, and not every household can afford them. Some cities and counties open clean-air spaces during smoke events, and local health departments typically announce locations when air quality worsens.
The researchers say future work will try to identify which chemical components make wildfire smoke more toxic and how those particles affect the body. For now, the evidence supports treating smoke days as a health event, especially for relatives who are older or chronically ill.
Key Questions Answered
What did the Mount Sinai studies find? Wildfire smoke particles were associated with greater risks of heart and lung hospitalization than equal amounts of other fine particle pollution, and with poorer survival in older adults with lung cancer.
Who is most at risk from wildfire smoke? Older adults, people with heart or lung disease, cancer patients, pregnant people, young children, outdoor workers, and households without good air filtration.
Do these studies prove smoke causes these outcomes? No. They show strong associations in large datasets, but exposure was estimated by location, and other factors may play a role.
How can families reduce exposure? Check the Air Quality Index, stay indoors with windows closed, use HEPA filtration if possible, and wear a fitted N95 respirator outdoors during heavy smoke.
Does smoke only matter near wildfires? No. Smoke can travel hundreds of miles and has affected major cities far from active fires.
