Study Links Long-Term Wildfire Smoke Exposure to Increased Cancer Risk

A study presented at the American Association for Cancer Research Annual Meeting in 2026 has found that long-term exposure to wildfire smoke was associated with a significantly increased risk of developing several types of cancer. The research analyzed data from over 91,000 participants and quantified exposure using fine particulate matter and satellite data.

Study Methodology and Scope

The research team analyzed data from 91,460 participants in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, tracking them from 2006 to 2018.

To assess wildfire smoke exposure, researchers used three metrics derived from participants' residential areas:

• Fine particulate matter (PM 2.5) attributed to wildfire smoke.
• Black carbon levels from wildfire smoke.
• Satellite-derived counts of days with wildfire smoke plumes.

The study calculated 36-month moving averages of these exposure levels for each participant. The median exposure levels among participants were:

• 0.37 µg/m³ for wildfire smoke PM 2.5
• 0.0083 µg/m³ for wildfire smoke black carbon
• 1.94 days for monthly plume-day counts

Reported Findings on Cancer Risk

The analysis identified a significant association between increased long-term wildfire smoke exposure and a higher risk of several cancers, while no significant link was found for others.

Cancers with Increased Risk: Lung, colorectal, breast, bladder, and blood cancers.
Cancers with No Significant Association: Ovarian cancer and melanoma.

The study reported a linear dose-response relationship for PM 2.5 exposure. For every additional 1 µg/m³ in the 36-month moving average of wildfire smoke PM 2.5, the analysis indicated increased risks:

• Lung cancer risk increased by 92%.
• Colorectal cancer risk increased by 131%.
• Breast cancer risk increased by 109%.
• Bladder cancer risk increased by 249%.
• Blood cancer risk increased by 63%.

Similar associations were observed with increases in wildfire smoke plume-day counts. Increased black carbon exposure was significantly associated only with breast and bladder cancer risk.

Context and Researcher Statements

The study notes that wildfire smoke contains various toxins, including known carcinogens such as polycyclic aromatic hydrocarbons.

"The findings suggest chronic exposure to wildfire smoke may carry long-term cancer risks, even at the relatively low levels commonly experienced by the general population."
— Qizhen Wu, PhD, the study's first author

Shuguang Leng, MBBS, PhD, the senior author, noted that as wildfires continue to increase in frequency and intensity, understanding their long-term health impacts is becoming increasingly important.

Study Limitations and Funding

The researchers outlined several limitations to their analysis:

• Satellite data for wildfire smoke are only available from 2006, which may not capture the full period of cancer initiation due to the potential years-long delay between initiation and diagnosis.
• The location-based exposure assessment assumed participants were within their residential areas during every measured period and did not account for time spent indoors versus outdoors.
• The researchers stated that further investigation is warranted into how the origin and specific contents of wildfire smoke from different regions may affect cancer risk.

The study was funded by the National Institutes of Health. The study authors declared no conflicts of interest.