LA’s January 2025 wildfires didn’t just burn neighborhoods—they sparked a surge in heart, lung, and illness emergencies across the city.
A new Cedars-Sinai study reports that far more people than usual experienced heart attacks, lung problems, or general illness in the three months following the January 2025 wildfires in Los Angeles. The researchers found that these health issues appeared within 90 days of when the fires began, pointing to a rapid and measurable impact on the community.
“Wildfires that spread into urban areas have proven to be extremely dangerous because of how quickly they move and what they burn and release into the environment,” said Susan Cheng, MD, MPH, director of Public Health Research at Cedars-Sinai and senior author of the study, published today (December 17) in JACC. “Our research suggests the Eaton and Pacific Palisades fires had an immediate effect on people’s health.”
How researchers tracked emergency room visits
The Cedars-Sinai Emergency Department sits on the medical center’s main campus, roughly 10 miles from Pacific Palisades and about 20 miles from Altadena, where the largest Los Angeles fires started in January 2025.
Researchers analyzed emergency department visit records from January 7 to April 7, 2025, covering the first 90 days after the fires began. They then compared those numbers with data from the same calendar period between 2018 and 2024.
Overall emergency room traffic during that time did not change significantly compared with previous years. However, visits tied to specific medical problems rose sharply.
Sharp increases in illness, heart attacks, and lung problems
When investigators focused on particular conditions, they found striking differences. Visits for general illness increased by 118% compared with the average from the prior seven years. Emergency visits for heart attacks rose by 46%, while pulmonary illness visits climbed by 24% during the same period.
“Fine particles released by wildfires can enter the body and cause injury, particularly to the heart and lungs,” said Cheng, who is also the Erika J. Glazer Chair in Cardiovascular Health and Population Science in the Smidt Heart Institute at Cedars-Sinai. “Stress related to the fires may also contribute to a broad range of health issues.”
Unusual blood test findings after the fires
The study also uncovered changes that had not been widely reported after previous wildfire events. Abnormal blood test results linked to general illness more than doubled during the 90-day window in 2025 compared with the same timeframe in earlier years, according to the investigators.
“Abnormal blood test results could indicate that the body is responding to an external stressor such as toxins in the air,” said Joseph Ebinger, MD, MS, associate professor in the Department of Cardiology and first author of the study. “This study is an important step toward understanding how the Eaton and Palisades fires may have affected Angelenos’ health. We need more research to determine what we can do to mitigate any remaining risks and protect people from fire harm in the future.”
A decade-long effort to study wildfire health impacts
This research is part of the broader LA Fire HEALTH Study, a long-term collaboration focused on understanding the health consequences of the January 2025 fires in L.A. County. Scientists from Cedars-Sinai; the Harvard T.H. Chan School of Public Health; the Keck School of Medicine of the University of Southern California (USC); Stanford University; UCLA; the University of California, Davis (UCD); the University of California, Irvine (UCI); the University of Texas at Austin; and Yale University plan to continue studying the fires’ effects on health over the next 10 years.
Reference: “Emergency Encounters for Illness During and After the Los Angeles Wildfires” by Joseph E. Ebinger, MS, Tzu Yu Huang, MS, Sandy Y. Joung, MSHS, MBA, Juliane Louise F. Kwong, BS, Wasay Warsi, MS, BS, Nancy Sun, MPS, Jesse Navarrette, MPA, Patrick Botting, DHSc, Zaldy S. Tan, Brian L. Claggett, Alan C. Kwan and Susan Cheng, 17 December 2025, Journal of the American College of Cardiology.
DOI: 10.1016/j.jacc.2025.10.079
Additional Cedars-Sinai authors include Tzu Yu Huang, MS; Sandy Joung, MSHS, MBA; Juliane Kwong, BS; Wasay Warsi, MS, BS; Nancy Sun, MPS; Jesse Navarrette, MPA; Patrick Botting, DHSc; Zaldy S. Tan, MD, MPH; and Alan C. Kwan, MD.
Other authors include Brian L. Claggett, PhD, of Brigham and Women’s Hospital in Boston.
Funding: This work was partially supported by the Spiegel Family Fund, the Smidt Heart Foundation, and the Erika J. Glazer Family Foundation.
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