New research suggests that breathing wildfire smoke during pregnancy, especially late in pregnancy, may slightly increase the risk that a child is later diagnosed with autism. The findings come from a large California study examining how exposure to wildfire smoke particles may affect fetal brain development during critical growth periods.
Who Is Conducting the Research
The study was led by researchers from Tulane University, with collaboration from Kaiser Permanente Southern California, the University of Southern California, Harvard University, and Sonoma Technology. The research was published on January 20, 2026, in Environmental Science & Technology.
Senior author Mostafijur Rahman is an assistant professor of environmental health sciences at Tulane University’s Celia Scott Weatherhead School of Public Health and Tropical Medicine. Lead author David Luglio is a postdoctoral fellow at the same institution.
What the Study Examined
Researchers analyzed health records from more than 200,000 births in Southern California between 2006 and 2014. This region was chosen because it experiences frequent wildfires and also reports higher autism diagnosis rates than many other parts of the country.
Using maternal home addresses, the team estimated exposure to wildfire smoke during pregnancy by tracking levels of PM 2.5, extremely small particles that can enter the lungs and bloodstream. Exposure was assessed by trimester and measured by the number of smoky days and waves of smoke exposure above specific PM 2.5 thresholds.
Why the Third Trimester Matters
The strongest association between wildfire smoke and autism appeared during the third trimester, the final three months of pregnancy. This period is marked by rapid brain growth and the formation of major neural centers.
David Luglio explained that during late pregnancy, the fetal brain grows significantly in size and complexity, which may make it more vulnerable to environmental stressors such as air pollution and inflammation caused by inhaled smoke particles.
What the Researchers Found
Compared with pregnancies that had no wildfire smoke exposure during the third trimester, autism risk increased as smoke exposure increased.
The study found that autism risk was about 10 percent higher after one to five smoky days, about 12 percent higher after six to ten smoky days, and about 23 percent higher after more than ten smoky days.
The link was strongest among women who did not move during pregnancy, suggesting that ongoing exposure in the same location may matter more than occasional smoke exposure. Among these nonmovers, hazard ratios rose consistently with the number of wildfire smoke days and smoke waves.
Researchers identified 3,356 autism diagnoses by age five within the study population.
What Levels of Smoke Were Considered Risky
The study focused on wildfire-related PM 2.5 exposure above specific concentration thresholds of 3 and 5 micrograms per cubic meter. Researchers found that the number of days and waves of exposure mattered more than the average PM 2.5 concentration alone.
This suggests that short-term spikes of heavy smoke may pose a greater concern than lower levels of ongoing pollution.
Why Wildfire Smoke May Be Different
Rahman noted that wildfire smoke has a unique chemical makeup compared to everyday air pollution. It contains higher levels of carbon compounds, metals, and toxic byproducts released from burning vegetation and buildings. These exposures often occur in intense, short-term bursts rather than steady background pollution.
Inhalation of these particles can trigger inflammation and physiological stress, which scientists suspect may interfere with early brain development.
Alycia Halladay, chief science officer at the Autism Science Foundation, reviewed the findings and said they align with existing research linking prenatal air pollution exposure to autism.
She noted that while the increased risk is not large, it is consistent with prior studies and adds to a growing body of evidence connecting air pollution and neurodevelopmental outcomes.
David Mandell, a psychiatry professor at the University of Pennsylvania, urged caution in interpreting the results. He pointed out that the observed effects were small and that the exposure pattern was not perfectly consistent across all groups. He emphasized the need for replication before drawing firm conclusions.
Limitations of the Study
The researchers stressed that the study does not prove wildfire smoke causes autism. Correlation does not guarantee cause and effect. The team could not measure how much smoke women inhaled indoors or whether families used air purifiers, masks, or altered their behavior during wildfire events.
Other factors such as genetics, indoor air quality, and individual health conditions could also play a role.
Autism affects about 1 in 31 school-aged children in the United States, according to the Centers for Disease Control and Prevention. Scientists widely believe autism develops through a combination of genetic and environmental influences, particularly during early life.
Previous research, including a 2021 Harvard University study, has also found links between late-pregnancy air pollution exposure and autism risk.
Researchers say the results highlight the importance of minimizing smoke exposure during wildfire events, especially for pregnant women. As climate change increases the frequency and intensity of wildfires, understanding these risks becomes more important for public health planning and prevention.
Rahman emphasized that wildfire smoke is a potentially preventable environmental exposure, making mitigation efforts such as air filtration and public health guidance especially critical going forward.
HNZ Editor: This makes me a bit uncomfortable, seems like someone is trying to create a new kind of lawsuit. I also am disgusted with the 1 in 31 children number, it seems alarming, but the autism “experts” have redefined autism to include a whole lot of lesser conditions. This is about funding, not health.
