Mounting Evidence Shows Air Pollution Threatens Children's Cognitive Development

When we think about air pollution, most of us focus on its effects on our lungs and maybe our hearts. But new research reveals something more troubling: the air we breathe may affect children’s brains.

A team of UC Davis scientists systematically reviewed 40 different studies looking at how outdoor air pollution impacts the development of children’s brains. The research linked exposure to pollutants to changes in the brain. This includes differences in white matter, crucial for things like memory and learning, and even early signs of neurodegenerative diseases like Alzheimer’s.

“We’re seeing notable differences in brain outcomes between kids exposed to higher pollution levels and those with lower exposure,” said Camelia Hostinar, associate professor of psychology at UC Davis and the study’s corresponding author.

Children are especially vulnerable to air pollution for a few reasons. Their bodies and brains are still developing, and they breathe faster than adults, meaning they take in more air (and more pollutants) relative to their body size. And they spend a lot of time outside — whether that’s playing in the yard, walking to school, or just hanging out with friends. That outdoor time increases their exposure, particularly in cities or near freeways where pollution levels can spike.

“What should concern us in these studies and what they show is that fossil fuel pollution is literally damaging, not only things like the vasculature of infants and children’s brains but also what we call the cortical thickness, which is associated with cognitive capacities or cognitive deficits,” said Dr. Lisa Patel, a pediatrician for Stanford Children’s Health, who was not involved in the study.

The impact of pollution on young brains

Pollutants like fine particulate matter, what researchers refer to as PM2.5, and nitrogen dioxide from car exhaust, power plants and wildfires can penetrate deep into the lungs and bloodstream. From there, they can travel to the brain, where they can trigger inflammation, which contributes to cell loss within the central nervous system. This process may trigger cognitive decline, an increased risk for dementia, autism and attention deficit hyperactivity disorder.

The UC Davis research team examined studies primarily from the U.S., Mexico and Europe, with one each from Asia and Australia. Some used advanced imaging techniques like MRI scans, while others tested chemical compounds or even looked for signs of brain tumors.

“These are observational studies, so we can’t definitively say air pollution causes these brain changes,” said Dr. John Balmes, a physician-scientist at UCSF and UC Berkeley, whose research has shown links between early-life pollution exposure and reduced IQ by age 10. He was not involved in the UC Davis study. “But when so many studies show consistent results, the association becomes strong — strong enough to move toward causality.”

Researchers also looked at animal models to explore potential causal links. In these models, exposure to pollution led to brain changes similar to what’s observed in human children.

“Between what the animal models show, what these pathology results show, and what we know from the adult literature, connecting what we know from animal studies to humans is a reasonable assertion,” Patel said.

Reducing the risks

On days like Wednesday and Thursday, when the air district issues a Spare the Air Alert for the Bay Area due to unhealthy smog levels, health officials urge people, especially children and sensitive groups, to limit outdoor activities.

“Kids should probably not be exercising vigorously outside if they don’t have to,” Balmes said.

Patel suggested several other steps to reduce exposure to air pollution, particularly for children. Installing portable air purifiers in homes and schools can significantly improve indoor air quality, especially near high-traffic areas. If you’re looking for a new home, try to avoid areas near major roads or industrial zones. For those already living near pollution sources, weatherizing your home by sealing cracks and gaps to prevent dirty air from sneaking in.

The UC Davis researchers also encouraged other scientists to include air pollution data in studies related to brain health.

“Anyone researching brain development or health outcomes should be asking about air pollution exposure,” said Sally Hang, a Ph.D. student at UC Davis and the study’s first co-author. “It’s a simple yet critical factor that could deepen our understanding of how to protect future generations.”

As research mounts on connecting air pollution to poorer neurodevelopment, policymakers may need to rethink what they consider safe levels of pollution, particularly when it comes to the most vulnerable among us — our children.