Study Links Wildfire Smoke Exposure to Increased Autism Risk in Infants

A new study published Tuesday in the journal Environmental Science & Technology reports a significant association between exposure to wildfire smoke during pregnancy and a higher likelihood of autism spectrum disorder (ASD) diagnoses in children.

The research analyzed birth and health data from hundreds of thousands of deliveries in Southern California, focusing on periods of intense wildfire smoke. Researchers found that higher exposure to fine particulate matter (PM2.5) linked specifically to wildfire events corresponded with an increased risk of ASD.

Wildfire smoke contains extremely small particles—PM2.5 measures less than 2.5 micrometers in diameter—that can penetrate deep into the lungs and enter the bloodstream. Scientists believe these particles may reach the placenta and potentially affect fetal development through two primary pathways: direct exposure to toxic compounds and inflammation triggered by the mother’s immune response.

In the direct pathway, researchers suggest fine particles or chemical byproducts from smoke may cross into the fetal environment and disrupt early brain development. In the second pathway, wildfire smoke exposure may activate the mother’s immune system, increasing inflammatory markers such as cytokines. Elevated inflammation during pregnancy has been linked in past research to changes in fetal brain signaling and connectivity.

The study also indicates the risk may be stronger during sensitive developmental windows in pregnancy, although the authors note that high levels of smoke exposure at any stage could be concerning.

In response to the findings, health experts are urging stronger safety guidance for pregnant women living in wildfire-prone areas. Common advice such as “stay indoors” may not provide enough protection without proper filtration, since smoke particles can infiltrate homes through doors, windows, and ventilation systems.

Experts recommend improving indoor air quality during smoky periods by using high-efficiency filters, including MERV 13 or higher for central HVAC systems. For homes without central air or for added protection in bedrooms, portable HEPA air purifiers are advised to help create a cleaner indoor environment. If outdoor activity is unavoidable, specialists suggest using a properly fitted N95 or KN95 respirator, as cloth masks offer minimal protection against PM2.5.

Monitoring air quality in real time is also recommended so families can make informed decisions about limiting outdoor activity, increasing filtration, or relocating temporarily when conditions become hazardous.

Researchers say the findings highlight that wildfire smoke is not only a respiratory threat but may also pose risks to fetal neurodevelopment. With wildfires becoming more frequent and severe, the study adds to growing evidence that the long-term health impacts of smoke exposure could extend well beyond the duration of a fire season.