• Posted April 7, 2025

Ozone Pollution Increases Risk Of Childhood Asthma

Ozone air pollution increases the risk of asthma among preschoolers and kindergarteners, a new study says.

Relatively small increases in ozone smog in a child’s first two years of life is associated with an increased risk of asthma and wheeze at 4 to 6 years of age, researchers reported April 2 in JAMA Network Open.

However, ozone exposure didn’t increase risk of asthma at ages 8 and 9, results show.

“It’s a puzzling finding,” said lead researcher Logan Dearborn, a doctoral student with the University of Washington Department of Environmental & Occupational Health Sciences. “It’s something we spent a long time trying to consider, and I don’t know if we ever came up with a satisfying answer.”

“But these findings are important,” Dearborn added in a news release. “Even if we only see the effects early in life, there are still all kinds of associated health care costs and stresses for families.”

For the study, researchers analyzed data on more than 1,100 children from a federal research project investigating how environmental factors can affect children’s health. The children lived in six cities – Minneapolis; San Francisco; Seattle; Memphis, Tenn.; Rochester, N.Y.; and Yakima, Wash.

The team compared kids’ asthma and wheeze as reported by their moms to federal data on ozone pollution in their area.

Previous studies have linked childhood asthma to exposure to fine particulate and nitrogen dioxide air pollution, researchers said in background notes.

But it’s been unclear whether asthma can be triggered by exposure to ozone, the pollutant that most often exceeds U.S. air quality standards, researchers said.

Ozone pollution is formed when sunlight bakes emissions from cars, power plants and industrial facilities, according to the U.S. Environmental Protection Agency (EPA). 

Results showed that if toddlers are exposed to a relatively small increase in ozone exposure of 2 parts per billion, they have a 31% increased risk of asthma and 30% increased risk of wheeze at ages 4 to 6.

Ozone also stood out when researchers analyzed how exposure to mixtures of three common air pollutants – ozone, nitrogen dioxide and fine particulates – affected asthma risk, results show.

“We interpret trends, and what we can conclude from this analysis is that when ozone within the air pollution mixture was higher than about 25 parts per billion, we saw a higher probability of asthma regardless of the concentration of nitrogen dioxide,” Dearborn said.

“We found a relationship between ozone and asthma only when fine particulate matter was at or above median concentrations, giving novel evidence that the relationship between ozone and childhood asthma may depend on the concentration of other pollutants, like fine particulate matter,” he added.

Further research is needed to determine why ozone exposure doesn’t increase asthma risk at ages 8 and 9, and whether the risk increases again as children become tweens and teens, researchers said.

But these results indicate that parents and regulators should take ozone pollution seriously when it comes to kids’ health.

“In the United States, ozone regulations only consider a very short time period,” Dearborn said. “We don’t regulate ozone over the long term, and that’s where this analysis fits in. Maybe we should be considering both a short- and a long-term threshold for the regulation of ozone.”

More information

The U.S. Environmental Protection Agency has more about ozone pollution.

SOURCE: University of Washington, news release, April 2, 2025