November 12, 2026
New research finds the later months of pregnancy may be an especially sensitive time
PHOENIX (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 in your area, visit AllergyandAsthmaRelief.org. The ACAAI Annual Scientific Meeting is Nov. 12-16 in Phoenix. For more news and research from the ACAAI Scientific Meeting, go to our newsroom and follow the conversation on X/Twitter #ACAAI26.
About ACAAI
The American College of Allergy, Asthma & Immunology (ACAAI) is a professional medical organization of more than 6,500 allergists-immunologists and allied health professionals, headquartered in Arlington Heights, Ill. Founded in 1942, the College fosters a culture of collaboration and congeniality in which its members work together and with others toward the common goals of patient care, education, advocacy, and research. ACAAI allergists are board-certified physicians trained to diagnose allergies and asthma, administer immunotherapy, and provide patients with the best treatment outcomes. For more information and to find relief, visit AllergyandAsthmaRelief.org. Join us on Facebook, Instagram, Threads and X.
EFFECT OF PRENATAL WILDFIRE EXPOSURE ON ASTHMA DEVELOPMENT
R141
A. Nguyen*, A. Goodrich, Y. Ren, K. Kim, R. Schmidt, Sacramento, CA.
Introduction
In the past few years, multiple wildfires caused devastating destruction in Northern California, affecting millions, especially pregnant women and children who are particularly vulnerable. Our study aims to investigate the impact of wildfire smoke on developing fetal lung.
Methods
Analyses included 1097 full term (≥ 37 gestation weeks) children. 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. Daily air pollution exposures were estimated using a hybrid modeling approach that captured estimate PM2.5 exposure for each subject. A Cox proportional hazards model combined with distributed lag nonlinear model was used to evaluate the associations of asthma and wheezing with PM2.5 exposure and wildfire (WF)-specific pollutant during pregnancy and infancy.
Results
Distributed lag models adjusting for child age, sex, gestational age, and secondhand smoking during pregnancy showed that increased PM2.5 exposure levels during second trimester and increased WF-specific pollutant during third trimester and at birth were significantly associated with early childhood asthma development.
Conclusion
Prenatal exposures to PM2.5 and WF-specific pollutants, especially during second and third trimester, were associated with later development of asthma. In identifying sensitive window of gestation exposure to wildfire smoke, this can help shape preventive strategies that mitigate maternal exposure and ultimately protect children’s health.
