As wildfires become increasingly common and severe across the United States and globally, concerns about their health impacts have grown. Now, a groundbreaking study presented at the annual meeting of the American Association for Cancer Research (AACR), held April 17 – 22, 2026, reveals that prolonged exposure to wildfire smoke (WFS) may significantly raise the risk of developing multiple types of cancer, including lung, colorectal, breast, bladder, and blood cancers.
Understanding the Risks
Wildfire smoke is known to contain a complex mixture of toxic substances, including carcinogens such as polycyclic aromatic hydrocarbons, benzene, and formaldehyde, as well as heavy metals. While the connection between air pollution and health problems is well established, the full-body effects of WFS on cancer risk have remained unclear—until now.
“Wildfire smoke exposure is not only a short-term respiratory or cardiovascular concern—but chronic exposure may also carry long-term cancer risks,” noted Qizhen Wu, Ph.D., a postdoctoral fellow at The University of New Mexico (UNM) Comprehensive Cancer Center and first author of the study.
The Study: Large-Scale Data and Real-World Exposure
Wu and colleagues, including senior author Shuguang Leng, MBBS, Ph.D., associate professor at the UNM Comprehensive Cancer Center, analyzed data from over 91,000 participants in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial (NCT00339495). None of the participants had a prior history of these cancers at enrollment (1993-2001).
To assess exposure, researchers used ground-level air pollution data and satellite imagery from 2006 onward to track levels of fine particulate matter (PM2.5) and black carbon—key components of wildfire smoke—at participants’ residences. They also counted the number of days each area was exposed to wildfire smoke plumes.
Shuguang Leng, MBBS, PhD, associate professor at the UNM Comprehensive Cancer Center. Photo courtesy: © 2026 AACR. Used with permission.Study outcome
Within the PLCO trial, 91,460 participants were evaluable for WFS exposure. From 2006 to 2018, the researchers calculated 36-month moving averages updated monthly for each participant’s exposure to WFS as defined by micrograms per cubic meter (µg/m3) for PM2.5 and black carbon and days of exposure for WFS plume-day counts. The median of those moving averages was 0.37 µg/m3 for WFS PM2.5, 0.0083 µg/m3 for WFS black carbon, and 1.94 days for monthly WFS plume-day counts.
During the same time period, Wu, Leng, and colleagues identified 1,758 lung cancer cases; 800 colorectal cancer cases; 1,739 breast cancer cases; 242 ovarian cancer cases; 896 bladder cancer cases; 1,696 blood cancer cases; and 1,127 melanoma cases.
Using a statistical analysis method that allows scientists to examine nonlinear risk associations, the researchers confirmed that WFS exposure was significantly associated with an increased risk of developing lung, colorectal, breast, bladder, and blood cancer. There was no evidence of deviation from a linear dose-response relationship. Associations with ovarian cancer and melanoma were not significant.
The team also found that the risk of developing these cancers increased with every additional 1 µg/m3 in the 36-month moving average of WFS PM2.5. Every 1 µg/m3 increase in WFS PM2.5 exposure was associated with significantly greater likelihoods of developing cancer: 92% greater risk of lung cancer; 131% greater risk of colorectal cancer; 109% greater risk of breast cancer; a 249% greater risk of bladder cancer; and a 63% greater risk of blood cancers.
The associations between increased exposure levels and risk for various cancers were similar for WFS plume-day counts. However, the associations between increased WFS black carbon exposure and risk of cancer development were only significant for breast and bladder cancer.
Implications for Public Health
“For the general public, the key message is that wildfire smoke is not only a short-term respiratory or cardiovascular concern—chronic exposure may also carry long-term cancer risks,” Wu said. “Increased cancer risk may occur even at relatively low levels of wildfire smoke PM2.5 commonly experienced by general populations.”
Leng emphasized that these findings have major implications as wildfires worsen due to climate change. “Wildfire smoke has emerged as a major source of ambient air pollution, reversing decades of improvement achieved under the Clean Air Act.”
The study, funded by the National Institute of Health (NIH), highlights the need for further research—especially to understand how the source and composition of wildfire smoke might affect cancer risk for different populations. The researchers also noted limitations, including reliance on satellite data available only from 2006, and assumptions about participants’ locations during exposure periods.
Summary of Key Findings
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Protecting Yourself from Wildfire Smoke
Nearly half of the U.S. population now lives in areas with unhealthy levels of air pollution, according to the American Lung Association. While immediate effects of wildfire smoke—like respiratory irritation—are well known, the potential for increased cancer risk underscores the importance of minimizing exposure:
- Stay indoors with windows and doors closed during wildfire events.
- Use air purifiers and avoid activities that further pollute indoor air.
- Follow local air quality alerts and evacuation orders when necessary.
- Wear masks designed to filter fine particles if you must go outside.
Looking Ahead: a wake-up call
As wildfires continue to increase in frequency and intensity, understanding their long-term health impacts is more important than ever. The new research presented at AACR 2026 serves as a wake-up call for individuals, communities, and policymakers to take action—both to limit exposure to wildfire smoke and to support further research into its health effects.
Study limitations
Limitations of this study include that data from satellite images are only available from 2006, which precluded analysis of wildfire smoke’s role in cancer initiation due to the sometimes years-long delay between cancer initiation and cancer diagnosis. Additionally, the location-based analysis assumed that participants were within their residential areas during every measured exposure period and did not account for time spent indoors versus outdoors.
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Clinical trials
Prostate Lung Colorectal and Ovarian (PLCO) Cancer Screening Trial – ClinicalTrials.gov ID NCT00339495
References
[1] Wu Q, Sinclair L, Pankratz VS, Lan Q, Rothman N, Jones R, Zhang S, Shuguang Leng S. Wildfire smoke and cancer risk in the United States: Evidence from the PLCO Trial In: Proceedings of the 117th Annual Meeting of the American Association for Cancer Research; 2026 April 17-22; San Diego, CA.: AACR; 2026. Abstract nr 6252 / 14
Featured image: Taken on the day the Calwood fire started from the Peak to Peak Highway. Showing the smoke plume created from the fire after growing to 8,000 acres within the first 5 hours, also capturing the empty road with the smoke behind it. Boulder County, CO, USA. Photo courtesy: © 2020 – 2026 Malachi Brooks on Unsplash. Used with permission.
DOI
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