Exposure to fine particles from wildfire smoke during pregnancy was associated with a higher risk of autism diagnosis in children, according to a study led by Rutgers University with researchers from the Harvard T.H. Chan School of Public Health and other institutions. It was published in JAMA Pediatrics on 26 October 2026.
The researchers analysed records for 893,212 mother-child pairs enrolled in Medicaid, the US health programme for people on lower incomes, with children born between 2007 and 2014. They used modelled estimates of weekly wildfire-related fine particulate matter (PM2.5) for each mother's residential ZIP code.
Each 0.75 microgram per cubic metre increase in the average concentration of wildfire-related fine particles during pregnancy was associated with a 30% higher risk of a later autism diagnosis. The associations were strongest during the second and third trimesters, and particularly for exposure after the 15th week of pregnancy. Fine-particle pollution from other sources was associated with a smaller increase in risk, and the study found no significant association between wildfire smoke and ADHD.
The authors stress that the study was observational and cannot establish that wildfire smoke causes autism. Its focus on Medicaid enrollees may limit how widely the findings apply, and unmeasured factors and uncertainty in the exposure estimates remain possible sources of bias. Because the births studied came before recent large wildfire smoke events, such as the 2023 Canadian wildfires, the authors call for further research in more recent groups of children.