As Extreme Fires Multiply, California Scientists Zero In on How Smoke Affects Pregnancy and Children

When wildfires spread through parts of Northern California wine country in 2017, they melted electronics, combusted cars and exploded propane tanks. The fires sent acrid smoke billowing into the sky, its footprint wafting over the state and extending for 500 miles into the Pacific Ocean. 

At the time, Rebecca Schmidt, a molecular epidemiologist at the University of California, Davis, was working on a study that followed families of children with autism who were expecting another child. When the fires spread, pregnant participants in the research started asking whether they should be worried about the air. 

Schmidt and her collaborators didn’t know what to say. There wasn’t much existing research on how wildfire smoke affects pregnancy. “I would have been wondering the same thing,” she said. “We really couldn’t tell them how concerned they needed to be.”

She decided to try to find the answers herself. Over the last several years, Schmidt and a team of fellow scientists have collected biological samples like hair, saliva and blood from pregnant people in California to better understand the health effects of smoke exposure on babies and those who carry them. 

The study’s timeline overlapped with numerous huge fires in the state, and researchers are still assessing the results. But the number of participants wasn’t large enough to fully understand the relationship between exposure and birth outcomes or developmental health. 

Now, Schmidt and a team of researchers are expanding the scope, examining two decades of statewide health and birth records alongside wildfire smoke data to determine which pockets of California are bearing the brunt of the smoke and what effects that environmental exposure could be having on early life. The results could have wide-reaching implications for locations experiencing similar spikes in hazardous fires.

“It’s only going to get worse with climate change,” Schmidt said. “Learning about it is relevant for everybody.”

The team, which includes nine researchers from UC Davis and the University of California, Los Angeles, will be led by Schmidt and Miriam Nuño, a UC Davis biostatistician who researches public health and health disparities. In addition to identifying communities where wildfire smoke may be causing harm and analyzing health impacts, the scientists will engage with community members on ways they can better protect themselves, like wearing N95 masks or installing relatively cheap indoor air filters. 

Both Nuño and Schmidt have long studied human health. And both grew up in areas where air pollution was a part of daily life. 

Born and raised in Iowa, Schmidt drove past agricultural fields where pesticides at times hung in the air like a “brown shroud” on her way to school. She lived in the state through graduate school, earning her Ph.D. in epidemiology at the University of Iowa. When she moved to California in 2008, the state was experiencing drought and a devastating fire year. 

“I remember thinking, ‘Is it going to be like this every year?’” she said. “I’ve definitely had to modify my life around smoke exposure.”

Nuño moved to California from Guadalajara when she was 14, settling in Los Angeles and then the city of Riverside, about 60 miles east. In areas inland of Los Angeles, smog and pollution blow in from the west and sit there, with nearby mountains preventing dispersal. At the time, she didn’t realize poor air quality was a problem there, she said,  and she didn’t expect to pursue health-related research. 

“Those clouds of gray smoke—I never grew up realizing that was even an issue,” she said. “Often, you worry about other things, like do you have enough to eat and things like that.”

Nuño studied pure mathematics at the University of California, Riverside, and planned on getting her Ph.D. in applied math and biostatistics, although she couldn’t entirely envision a future limited to studying mathematical concepts. Then, while in graduate school, she attended a lecture on math and HIV modeling. “That was really the change for me,” she said. “I want to do research that people can read about, and it can have some change.” 

After studying math and computational biology during her Ph.D. work at Cornell University and completing fellowships in biostatistics at the Harvard School of Public Health and UCLA, Nuño increasingly focused her research on real-world health data. 

When the Covid-19 pandemic arrived in 2020, she began working with the city of Davis to forecast infection rates. It was her “first taste,” she said, of how her skills could help focus resources like testing and vaccination to reduce the disproportionate health impacts in underserved communities. Mathematical modeling and statistical analysis are powerful, she said, “but if you’re not looking with the lens of equity and health equity, then you’re missing the picture.”

This study on wildfire smoke is Nuño’s first collaboration with Schmidt. Their work will be funded by a $1.35 million grant from the U.S. Environmental Protection Agency focused on environmental justice and climate-related health impacts on vulnerable populations and on life stages.

To date, only a few studies have looked at the impact of wildfire smoke on birth outcomes, such as a 2022 paper from scientists at Stanford University that attributed nearly 7,000 preterm births from 2006 to 2012 in California to wildfire smoke exposure. 

Past research has largely focused on the years preceding California’s parade of record-breaking wildfires in the last decade. By focusing on a more recent time period that encompasses those extreme fires, the UCLA and UC Davis research may yield different findings from the earlier research, said Amy Padula, an epidemiologist at the University of California, San Francisco’s School of Medicine, who is using California birth records to conduct separate research on wildfire-related air pollution and birth outcomes from 2007 to 2020. 

More research is needed, said Nuño, in part because of the size of climate-worsened fires but also because of where they’re burning. As people move into forested areas and wildfires spread to inhabited zones, the flames are combusting not just trees and vegetation but also homes and all of the objects inside them. That changes the chemical makeup of smoke and the dangers of exposure. 

The team is currently mapping the parts of the state that are at high risk for smoke exposure. Then the group will determine where that exposure varies, and how that intersects with race, income level, exposure to pollutants and other factors. In addition to looking at birth weight and gestational age, the team will examine health data on developmental outcomes and autism diagnoses. 

While data collected from birth records and from measuring wildfire smoke, birth outcomes and later development will guide their work, collaborators are paying close attention to communities where many people spend a lot of time outside, such as agricultural areas where many farmworkers live. 

Communities of color and low-income communities experience disproportionate air pollution, and the team expects the same will be true for wildfire exposure.

“All of this is systemic,” said Natalia Deeb-Sossa, a sociologist and professor of Chicana/o studies at UC Davis, who is working on the team. “Wildfires are now every year more and more common because of climate change. I believe that is something that is affecting more and more of our more vulnerable communities and populations, and I think it’s really important that we do something about it.”

Past research has linked air pollution to lower birth weights and preterm births, which can have a negative impact on health later in life. The California study, which will run into 2025, could provide more clarity on the extent to which those effects also result from wildfire smoke, for those inside and outside of the state.

“The whole world’s been impacted by wildfire smoke at this point,” Schmidt said. “It’s not easy to run from anymore.”