Pregnant women’s exposure to wildfire smoke — especially during the third trimester — may increase the risk of autism in their children, according to new research covering hundreds of thousands of births in Southern California.
The study, published Tuesday in the journal Environmental Science & Technology, is the first to examine a potential link between prenatal exposure to wildfire smoke and autism. Previous research suggested that pregnant women’s exposure to air pollution more generally, including smog released from vehicles, smokestacks, and lead, may be linked to the developmental disorder.
The new research focused on exposure to PM 2.5, tiny particles found in wildfire smoke that can lodge deep in the lungs and enter the bloodstream, raising major health concerns. To estimate smoke exposure, the researchers used a model to estimate PM 2.5 levels in each individual’s home during pregnancy.
“This paper supports other scientific research that links prenatal exposure to air pollution, particularly PM 2.5, to autism,” said Alycia Halladay, scientific director of the nonprofit Autism Science Foundation, who was not involved in the study. “The magnitude of the risk is not huge, but it is consistent with other research and adds to a body of scientific literature linking air pollution and autism.”
“Autism and wildfires are on the rise, and this study is just the beginning of research into the links between the two,” said study lead author Mostafijur Rahman, assistant professor of environmental health sciences at Tulane University’s Celia Scott Weatherhead School of Public Health and Tropical Medicine.
How big is the risk?The study analyzed health records from more than 200,000 births in Southern California from 2006 to 2014. California, researchers said, leads the nation in the amount of land burned each year by wildfires and the rate of childhood autism diagnoses.
The increased risk was stronger when mothers were exposed to wildfire smoke during the third trimester (the last three months of pregnancy), particularly during multiple smoke days, rather than from overall average pollution levels alone, the study found.
The risk of autism diagnosis was approximately 10% higher for children whose mothers experienced 1 to 5 days of smoking during the third trimester, 12% higher with 6 to 10 days, and 23% higher with more than 10 days.
The association was clearest among women who did not change residence during pregnancy, suggesting that prolonged exposure to the same location – and not just casual smoking – may play an important role.
The study, however, does not explain why smoke from wildfires may increase the risk of autism.
Rahman said wildfire smoke is very different from other pollutants, such as traffic pollutants, that people are exposed to almost daily.
“Wildfire smoke has a unique chemical composition,” he said, “including higher levels of carbon compounds, metals and toxic byproducts, and it tends to occur in intense, short-term peaks. »
The third trimester is a critical period in fetal development, said the study’s lead author, David Luglio, a postdoctoral researcher at the Celia Scott Weatherhead School.
“When it comes to the brain, and at the end of the term, that’s when the brain really grows and develops its major centers,” he said. He added that the findings should not cause alarm, noting that autism is not limited to environmental factors, but is also believed to have a strong genetic component.
Halladay said exposure to high levels of PM 2.5 has previously been linked to low birth weight, higher levels of premature births, asthma and obesity.
“Close monitoring as well as mitigation of air pollution should be a priority for regulatory agencies in the future,” she said.
Further research is neededAutism spectrum disorder – characterized by problems with social and communication skills and repetitive behaviors – affects 1 in 31 school-age children in the United States, according to the Centers for Disease Control and Prevention.
This disorder is thought to be “multifactorial,” said Dr. Akhgar Ghassabian, associate professor of pediatrics and population health at NYU Grossman School of Medicine, and several environmental factors “are involved, particularly if these environmental exposures occur early in life.”
Health and Human Services Secretary Robert F. Kennedy Jr., with the support of President Donald Trump, has made autism a high-profile research priority, saying health officials want to better understand the “root causes” of the disease, including potential environmental causes, such as air pollution, chemicals and medications. Kennedy also promoted unproven treatments, including leucovorina synthetic form of vitamin B9 or folate, which the body needs to make healthy blood cells.
In September, Trump claimed without new evidence that acetaminophen — the active ingredient in the painkiller Tylenol — was a cause of autism, a statement that sparked intense pushback from obstetrician-gynecologists, autism advocacy groups and international health organizations, such as the World Health Organization. Big new analysis found no link between acetaminophen and autism.
David Mandell, a professor of psychiatry at the University of Pennsylvania, said the idea that exposure to wildfire smoke might increase autism risk is largely consistent with previous research linking exposure to air pollution during maternal pregnancy to poorer neurodevelopmental outcomes in children.
But he said he was cautious about how the study results were interpreted, noting that the observed effects were small and that the most exposed group did not show a clear increase in risk.
“They do see higher risk at the second highest exposure level during the third quarter among nonmovers, but not at the highest exposure level,” Mandell said. “This lack of dose response makes me skeptical of the results. I would definitely want to see a replication before putting a lot of stock into it.”
The authors note that the study has limitations: Exposure estimates were based on outdoor air, and researchers don’t know how much smoke people were exposed to indoors, or whether they used air filters, wore masks, or changed their behavior during a wildfire. Rahman said further studies were still needed.
The findings, he said, “reinforce the importance of minimizing exposure to smoke during a wildfire when possible and following public health guidelines.”
Mandell said he hoped an administration “truly interested in improving outcomes for children would strengthen” the Environmental Protection Agency and strengthen the Federal Emergency Management Agency “to reduce pollution and help families cope.”
“This administration seems to be going in an absolutely opposite direction,” he said.
Rahman said he’s also curious about whether prevention — like masks or air purifiers — can reduce the risk seen in the study.
“Wildfire smoke is a potentially avoidable environmental exposure,” he said.
Berkeley Lovelace Jr. is a health and medical reporter for NBC News. He covers the Food and Drug Administration, with a particular focus on Covid vaccines, prescription drug pricing and health care. He previously covered the biotech and pharmaceutical industry with CNBC.