- August 14, 2026
- By Fid Thompson
As this year’s wildfires set new records for acres burned, destroying homes and businesses and ravaging communities, a new University of Maryland study finds their smoke may also be harming unborn babies more than ever before.
Wildfire smoke in the United States comprises a rising proportion of air pollution experienced by infants before birth, more than doubling from 2003 to 2019, according to the study published Aug. 6 in Frontiers in Environmental Health. Air pollution experienced during this prenatal period has been linked to premature birth and low birth weight, which are among the leading causes of infant illness and death.
The team of researchers from the School of Public Health and the Department of Atmospheric and Oceanic Science found that by the end of the study period, wildfire smoke contributed about 4% to 13% of the average daily air pollution experienced before birth, depending on where the mother lived.
“Although extremely bad air days have become far less common, most of the ones that remain are now attributable to wildfire smoke,” said Menglu Liang, assistant clinical professor in biostatistics and lead author.
She and colleagues analyzed prenatal exposures to PM2.5, tiny particles 30 times smaller than a human hair that people can inhale from various polluting sources such as power plants, industrial exhaust, wildfires and fossil fuel-powered vehicles. These fine particles pose a risk to human health and have been linked to adverse birth outcomes.
The study analyzed over 64 million live births in 48 states between 2003 and 2019. They linked these birth records to pollution measures from an atmospheric model that estimated daily air pollution from different sources, including wildfires. This model allowed the researchers to estimate how much of total air pollution was attributable to smoke versus other sources.
Researchers tracked the average daily exposure to PM2.5 during the prenatal period and the number of prenatal days that exceeded the Environmental Protection Agency’s quality standard for particulate matter.
The increased role that wildfire smoke plays in prenatal pollution exposure is partially explained by the fact that U.S. regulations and cleaner technologies have reduced exposure to other sources of pollution, such as from industry or vehicles, the researchers said.
They found that pollution from these sources dropped by 37% and the chance of gestational mothers being exposed to an extremely bad air day caused by a non-fire source plummeted by about 85%. Nationally, however, the share of extreme pollution days attributable to wildfire smoke climbed from 22% to 65%.
The study also found that wildfire’s share of air pollution grew fastest in places that already face other disadvantages: lower-income counties, rural areas, communities with large American Indian and Alaska Native populations and areas with few maternity and neonatal care services..
“As more people increasingly encounter wildfire smoke, we need to proactively help communities avoid exposures when they can and access appropriate medical care when they experience an adverse reaction,” said co-author Michel Boudreaux, associate professor of health policy and management.