PHOENIX, Ariz. (Nov. 12, 2026) – Babies whose mothers breathed in wildfire smoke and other air pollution during the middle and later months of pregnancy were more likely to develop asthma as young children. That's according to a new study being presented at the American College of Allergy, Asthma and Immunology (ACAAI) 2026 Annual Scientific Meeting.
Devastating large wildfires burned across Northern California from 2017 to 2020, spreading smoke over areas where millions of people live. Pregnant women and young children are among those most at risk from any smoke exposure, including wildfire. A baby's lungs are still growing in the womb, so researchers wanted to know whether wildfire smoke during pregnancy could affect a child's breathing and lung health in later years.
"A baby's lung development begins before birth, and our study suggests that certain stages of pregnancy maybe be especially vulnerable to the effects of wildfire smoke," said Anh Nguyen, MD, lead author of the study and ACAAI member. "As wildfires become more frequent and affect larger population, knowing when the exposure poses the greatest risk can help families, healthcare providers, and public health officials to take steps to protect both mothers and babies."
The researchers studied 1,097 children who were born full-term in Northern California. 108 children were born from mothers who were pregnant during the 2017 – 2020 Northern California wildfires and were recruited from B-SAFE (Bio-Specimen Assessment of Fire Effects) study. 989 children who were born at UC Davis Medical center between 2017-2019 and from areas affected by the recent Northern California wildfires were also included through chart review.
The researchers estimated how much polluted air each mother breathed every day during pregnancy and after the baby was born. They looked at two things:
- Fine particulate matter (PM2.5): Tiny bits of pollution in the air, many times smaller than the width of a human hair. They can come from smoke, cars, and factories, and they can travel deep into the lungs.
- Wildfire pollution: Pollution that came from the wildfire smoke itself.
The researchers accounted for other things that can affect asthma development, such as the child's age and sex, how far along the pregnancy was at birth, family history of asthma and whether the mother was around cigarette smoke while pregnant. Then they found:
- More fine-particle pollution during the second trimester (months 4 to 6 of pregnancy) was linked to asthma in early childhood.
- More wildfire pollution during the third trimester (months 7 to 9) and around the time of birth was also linked to asthma in early childhood.
The study shows a link between wildfire smoke and asthma. It does not prove that smoke causes asthma. Still, knowing which months of pregnancy may matter most could help doctors offer pregnant women clearer advice during wildfire season. It could also help health leaders plan ways to protect pregnant women when the air is affected by smoke.
"Pregnant women can't control when a wildfire happens, but there are things they can do on smoky days," said Dr. Nguyen. "Staying indoors, keeping windows closed, and using an air purifier can help lower how much smoke they breathe in."
Abstract Title: Effect of Prenatal Wildfire Exposure on Asthma Development
Presenter: Anh Nguyen, MD
If your child's asthma is not well controlled, talk with a board-certified allergist about treatment options. To find an allergist near you, visit AllergyandAsthmaRelief.org . The ACAAI Annual Scientific Meeting is Nov. 12-16. For more news and research from the ACAAI Scientific Meeting, go to our newsroom and follow the conversation on X/Twitter #ACAAI26.
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