Wildfire Smoke and Dementia: What Scientists Now Know

Could Wildfire Smoke Affect Dementia Risk?

Wildfire smoke is well known to harm respiratory and cardiovascular health. Researchers are also investigating whether repeated or long-term exposure to wildfire smoke could affect the brain and contribute to dementia risk.

One large study of 1,228,452 Kaiser Permanente Southern California members aged 60 and older examined whether long-term exposure to wildfire-generated fine particulate matter, known as PM₂.₅, was associated with dementia diagnoses. The study used electronic health records from 2008 through 2019 and was originally published in JAMA Neurology in November 2024.

The original analysis reported that every 1 microgram-per-cubic-meter increase in three-year average wildfire PM2.5 exposure was associated with an 18% increase in the odds of receiving a dementia diagnosis. However, researchers later discovered a coding error in the way dementia cases were identified.

The paper was retracted and replaced on June 30, 2025. The error had incorrectly classified 5,413 people who did not have a dementia diagnosis as having dementia. Researchers also found that 5,345 people with Parkinson disease had incorrectly been excluded from the original study population.

After correcting the error, the estimated association was smaller. A 1 microgram-per-cubic-meter increase in three-year average wildfire PM2.5 exposure was associated with 12% higher odds of a dementia diagnosis. However, the result was not statistically significant. The adjusted odds ratio was 1.12, with a 95% confidence interval of 0.98 to 1.28. Because the confidence interval includes 1.00, the study could not rule out the possibility that the overall association was due to chance.

This does not mean wildfire smoke has been shown to be harmless to the brain. Rather, the corrected study did not establish a statistically significant association between long-term wildfire PM2.5 exposure and dementia in the overall study population.

What Is PM2.5?

PM2.5 refers to fine particulate matter that is 2.5 micrometers or smaller in diameter. These particles are small enough to travel deep into the lungs, and some particles or their components may enter the bloodstream.

Long-term exposure to PM2.5 from various sources has been associated with adverse health effects, including cardiovascular and respiratory disease. Researchers have proposed several possible ways air pollution could affect the brain, including inflammation, oxidative stress, blood-vessel dysfunction, and effects on the blood-brain barrier. These mechanisms, however, do not by themselves prove that wildfire smoke causes dementia.

Wildfire smoke can also differ chemically from pollution produced by traffic, industry, and other sources. Researchers are continuing to investigate whether these differences influence long-term health risks.

What Did the Study Find in Different Groups?

The corrected analysis found statistically significant associations between wildfire PM2.5 exposure and dementia diagnosis among participants who were younger than 75 at study entry and within a broad "Other" racial and ethnic category that included people reporting multiple races, American Indian or Alaska Native, Native Hawaiian or Pacific Islander, other, or unknown race and ethnicity.

These findings should be interpreted cautiously. Subgroup results do not prove that wildfire smoke causes dementia in these populations, and differences may reflect statistical variation, exposure patterns, socioeconomic conditions, health care access, or other factors.

Other Research

A separate study published in Alzheimer's & Dementia also examined long-term wildfire smoke exposure and dementia in a large California population. It found that each 1 microgram-per-cubic-meter increase in three-year average wildfire PM2.5 exposure was associated with 10% higher odds of a dementia diagnosis, but the confidence interval was 0.96 to 1.25, meaning the overall association was not statistically significant.

Together, these studies suggest that wildfire smoke and dementia deserve further investigation, but they do not establish that wildfire smoke causes dementia.

Why This Matters

Wildfires are an increasingly important source of PM₂.₅ exposure in many areas. Understanding the potential long-term effects of repeated smoke exposure is therefore an important public-health question.

For now, the connection between wildfire smoke and dementia remains uncertain. The strongest evidence continues to concern the immediate and well-established respiratory and cardiovascular harms of wildfire smoke. Nevertheless, the possibility of neurological effects is an important area for continued research.

During wildfire smoke events, reducing exposure remains important regardless of what future research finds about dementia. Following local air-quality advisories, keeping indoor air clean, limiting outdoor exposure when smoke levels are high, and using appropriate air filtration can help reduce exposure to wildfire smoke.

Sources

JAMA Neurology, “Wildfire Smoke Exposure and Incident Dementia”https://jamanetwork.com/journals/jamaneurology/fullarticle/2827124

National Institutes of Health, “Wildfire Smoke Exposure and Dementia Risk”https://www.alzheimers.gov/news/wildfire-smoke-exposure-and-dementia-risk

University of Washington, “Retracted and Replaced: UW-Led Research Links Wildfire Smoke Exposure With Increased Dementia Risk”https://www.washington.edu/news/2024/11/25/video-uw-led-research-links-wildfire-smoke-exposure-with-increased-dementia-risk/

Alzheimer’s & Dementia, “Long-Term Wildfire Smoke Exposure and Incident Dementia in a Large California Cohort”https://pmc.ncbi.nlm.nih.gov/articles/PMC11715301/