About . Birth before 37 weeks can lead to a cascade of health risks, both immediate and long-term, making prevention a vital tool for improving public health over generations.��

In recent years, researchers have identified a potential link between wildfire smoke — one of the fastest-growing sources of air pollution in the United States — and preterm birth, but no study has been big or broad enough to draw definitive conclusions. A new study led by the ����Ӱ�Ӵ�ý makes an important contribution, analyzing data from more than 20,000 births to find that pregnant people who are exposed to wildfire smoke are more likely to give birth prematurely.

“Preventing preterm birth really pays off with lasting benefits for future health,” said lead author , a UW postdoctoral researcher in environmental and occupational health sciences. “It’s also something of a mystery. We don’t always understand why babies are born preterm, but we know that air pollution contributes to preterm births, and it makes sense that wildfire smoke would as well. This study underscores that wildfire smoke is inseparable from maternal and infant health.”

In the study, ,��researchers used data from the , a federal research project focused on how a wide range of environmental factors affect children’s health. The sample included 20,034 births from 2006-2020 across the contiguous United States.

Researchers estimated participants’ average daily exposure to fine particulate matter, or PM2.5, generated by wildfire smoke, and the total number of days they were exposed to any amount of smoke. They estimated the intensity of smoke exposure by how frequently participants were exposed to wildfire PM2.5 levels above certain thresholds.

They found that pregnant people exposed to more intense wildfire smoke were more likely to give birth prematurely. In mid-pregnancy, exposure to any smoke was associated with an elevated risk of preterm birth, with that risk peaking around the 21st week of gestation. In late pregnancy, elevated risk was most closely associated with exposure to high concentrations of wildfire PM2.5, above 10 micrograms per cubic meter.

“The second trimester is a period of pregnancy with the richest and most intense growth of the placenta, which itself is such an important part of fetal health, growth and development,” said co-author , a UW professor of environmental and occupational health sciences and of pediatrics in the UW School of Medicine. “So it may be that the wildfire smoke particles are really interfering with placental health. Some of them are so tiny that after inhalation they can actually get into the bloodstream and get delivered directly into the placenta or fetus.”��

The link was strongest and most precise in the Western U.S., where people were exposed to the highest concentrations of wildfire PM2.5 and the greatest number of high-intensity smoke days. Here, the odds of preterm birth increased with each additional microgram per cubic meter of average wildfire PM2.5.

It’s possible those results were more precise simply because the West experiences more wildfire smoke on average, making the exposure model perform better, Sherris said. But there may be other factors behind the regional differences.��

The composition of wildfire smoke is different across the country. In the West, smoke tends to come from fires nearby, while in places like the Midwest, smoke has typically drifted in from faraway fires. and reacts with sunlight and airborne chemicals, which could have affected the results. Researchers also noted that external factors like co-occurring heat or housing quality may have effects that aren’t fully understood.��

Researchers hope that future studies will examine the exact mechanisms by which wildfire smoke might trigger preterm birth. But in the meantime, Sherris said, evidence for a link is now strong enough to take action.��

“There are a couple avenues for change,” Sherris said. “First, people already get a lot of public health messaging and information throughout pregnancy, so there’s an opportunity to work with clinicians to provide tools for pregnant people to protect themselves during smoke events. Public health agencies’ messaging about wildfire smoke could also be tailored to pregnant people and highlight them as a vulnerable group.”

Co-authors include , doctoral student of environmental and occupational health sciences at the UW; , clinical associate professor of environmental and occupational health sciences at the UW; , professor of biostatistics at the UW; , associate professor of environmental and occupational health sciences and of epidemiology at the UW; , postdoctoral fellow of epidemiology at the UW; and , assistant professor of environmental and occupational health sciences at the UW. A full list of co-authors is included with the paper.

This research was funded by the Environmental influences on Child Health Outcomes (ECHO) program at the National Institutes of Health under multiple awards. A full list of ECHO funding awards is included with the paper.��

For more information or to contact the researchers, email Alden Woods at acwoods@uw.edu.

Warmer weather across the globe is reshaping the landscape of human health. Case in point:��Dengue fever incidence could rise as much as 76% by 2050 due to climate warming across a large swath of Asia and the Americas, according to a new study led by , a researcher at the ����Ӱ�Ӵ�ý.��

Dengue fever, a mosquito-borne disease once confined largely to the tropics, often brings flu-like symptoms. Without proper medical care, it can escalate to severe bleeding, organ failure, and even death. ��

The study,, is the most comprehensive estimate yet of how temperature shifts affect dengue’s spread. It provides the first direct evidence that a warming climate has already increased the disease’s toll.����

“The effects of temperature were much larger than I expected,” said Childs, a UW assistant professor of environmental and occupational health sciences who conducted much of the research as a doctoral student at Stanford University. “Even small shifts in temperature can have a big impact for dengue transmission, and we’re already seeing the fingerprint of climate warming.”��

The study analyzed over 1.4 million observations of local dengue incidence across 21 countries in Central and South America and Southeast and South Asia, capturing both epidemic spikes and background levels of infection.����

Dengue thrives in a “Goldilocks zone” of temperatures — incidence peaks at about 27.8 degrees Celsius, or 82 degrees Fahrenheit, rising sharply as cooler regions warm but dropping slightly when already-hot areas exceed the optimal range. As a result, some of the largest increases are projected for cooler, high-population regions in countries such as Mexico, Peru and Brazil. Many other endemic regions will continue to experience larger, warming-fueled dengue burdens. By contrast, a few of the hottest lowland areas may see slight declines.����

Still, the net global effect is a steep rise in disease.��

The findings suggest that higher temperatures from climate change were responsible for an average 18% increase of dengue incidence across 21 countries in Asia and the Americas from 1995 to 2014 — translating to more than 4.6 million extra infections annually, based on current incidence estimates. Cases could climb another 49% to 76% by 2050 depending on greenhouse gas emissions levels, according to the study. At the higher end of the projections, incidence of dengue would more than double in many cooler locations, including areas in the study countries that are already home to over 260 million people.����

“Many studies have linked temperature and dengue transmission,” said senior author, a professor of biology in the. “What’s unique about this work is that we are able to separate warming from all the other factors that influence dengue — mobility, land use change, population dynamics — to estimate its effect on the real-world dengue burden. This is not just hypothetical future change but a large amount of human suffering that has already happened because of warming-driven dengue transmission.”��

The researchers cautioned that their estimates are likely conservative. They do not account for regions where dengue transmission is sporadic or poorly reported, nor do they include large endemic areas such as India or Africa where detailed data is lacking or not publicly available. The researchers also highlighted recent locally acquired cases in California, Texas, Hawaii, Florida, and in Europe — a signal of the expanding range of dengue. Urbanization, human migration and the evolution of the virus could amplify risks, while medical advances may help blunt them, making projections uncertain.��

Aggressive climate mitigation would significantly reduce the dengue disease burden, according to the study. At the same time, adaptation will be essential. This includes better mosquito control, stronger health systems and potential widespread use of new dengue vaccines.��

In the meantime, the findings could help guide public health planning and strengthen efforts to hold governments and fossil fuel companies accountable for climate change damages. Attribution studies are increasingly entering courtrooms and policy debates, used to assign responsibility for climate damages and to support funds compensating countries most affected.����

“Climate change is not just affecting the weather — it has cascading consequences for human health, including fueling disease transmission by mosquitoes,” Mordecai said. “Even as the U.S. federal government moves away from investing in climate mitigation and climate and health research, this work is more crucial than ever for anticipating and mitigating the human suffering caused by fossil fuel emissions.”��

Co-authors of the study include of Arizona State University, of the University of Maryland, and of Stanford. Lyberger and Harris completed much of their work while at Stanford.������

The research was funded by the Illich-Sadowsky Fellowship through the Interdisciplinary Graduate Fellowship program at Stanford University; an Environmental Fellowship at the Harvard University Center for the Environment; the National Institutes of Health; the National Science Foundation (with the Fogarty International Center); �ٳ��  �ٳ��  and the Stanford Woods Institute for the Environment.��

Adapted from a. For more information or to contact the researchers, email Alden Woods at acwoods@uw.edu.