Two major new studies are raising fresh concerns about the long-term health consequences of wildfire smoke, identifying a significant association between prenatal exposure to smoke and an increased likelihood of autism diagnoses in young children. The findings add to growing evidence that wildfire pollution may have deeper and more lasting neurological effects than previously understood.
The research, published in the peer-reviewed journals Environmental Science and Technology and Environment International, analyzed millions of birth records in California and found that exposure to wildfire smoke particularly during late pregnancy was linked to higher rates of autism spectrum disorder diagnoses in children.
Third Trimester Exposure Shows Strongest Association
The first study examined data from more than 200,000 children born in Southern California between 2006 and 2014. Researchers found that children whose mothers were exposed to 10 or more days of wildfire smoke during the third trimester had a 23 percent higher risk of being diagnosed with autism by age five. Those exposed to six to 10 days of smoke saw a 12 percent increase in risk.
Notably, the overall concentration of smoke across the full pregnancy did not show a strong link. Instead, the number of smoke exposure days during the third trimester appeared to be the most significant factor. Even a single day of exposure during this period showed measurable association.
The second study expanded the scope dramatically, analyzing approximately 8.5 million births in California between 2001 and 2019. While the overall association between average smoke exposure and autism was modest, the link became substantially stronger among women exposed to intense smoke events particularly those in the highest 10 percent of exposure levels.
For women in this highest exposure group who otherwise lived in areas with relatively low background air pollution, the odds of having a child diagnosed with autism were 50 percent higher compared to those with lower wildfire smoke exposure. Researchers adjusted their findings to account for other pollution sources such as vehicle emissions and urban smog.
Smoke’s Health Risks Extend Beyond Lungs
Wildfire smoke is widely considered more toxic than many other forms of air pollution. Fine particulate matter released during the burning of vegetation can penetrate deep into the lungs and enter the bloodstream, aggravating respiratory conditions and potentially affecting internal organs. Scientists have increasingly suspected that these particles may also influence brain development, though the exact biological mechanisms remain unclear.
Autism spectrum disorder currently affects approximately 1 in 31 eight-year-olds in the United States. While researchers widely agree that genetics play a major role in autism, environmental factors are also believed to contribute in complex and interacting ways.
Experts caution that the new studies do not prove that wildfire smoke directly causes autism. Instead, they identify an association a statistical link that warrants further investigation. Researchers emphasize that autism is likely influenced by multiple genetic and environmental factors working together.
The findings arrive as wildfires grow more frequent and severe in parts of the world due to climate change. As smoke events become more common and prolonged, understanding their broader health consequences is becoming increasingly urgent.
Scientists say further research is needed to determine how smoke exposure may interact with fetal development and whether preventive measures such as limiting outdoor exposure or using high-efficiency air filtration could reduce potential risks.
For now, the studies underscore a sobering reality: the impacts of wildfire smoke may extend far beyond the visible flames, carrying consequences that could shape health outcomes years into the future.