A new study has found that even small increases in ozone air pollution during the first two years of a child’s life may significantly raise the risk of developing asthma and wheezing by the time they are 4 to 6 years old. The research, published on April 2 in JAMA Network Open, shows how exposure to this common pollutant can negatively affect children’s respiratory health early on.

Ozone, a harmful gas formed when sunlight reacts with emissions from vehicles, power plants, and factories, is known to frequently exceed U.S. air quality standards. Researchers say that exposure to just a 2-parts-per-billion increase in ozone levels during toddlerhood was associated with a 31% increased risk of asthma and a 30 per cent increased risk of wheezing by preschool age.

Interestingly, the study found no increased risk of asthma in children aged 8 and 9, making the findings somewhat puzzling. “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,” said lead researcher Logan Dearborn, a doctoral student at the University of Washington's Department of Environmental & Occupational Health Sciences.

Despite the unclear reason for the lack of effect in older children, Dearborn emphasized the importance of the findings. “Even if we only see the effects early in life, there are still all kinds of associated health care costs and stresses for families,” he noted in a news release.

The research team analyzed data from over 1,100 children as part of a federal project studying how environmental factors impact child health. These children were from six cities across the US—Minneapolis, San Francisco, Seattle, Memphis, Rochester (NY), and Yakima (Washington). The researchers compared mothers’ reports of their children’s asthma and wheezing with federal records of local ozone pollution levels.

While earlier studies have linked childhood asthma to air pollutants like fine particulate matter and nitrogen dioxide, the impact of ozone alone has been less understood. This study suggests ozone should be taken more seriously when it comes to children’s health.

When the researchers studied the effects of ozone alongside other common pollutants—nitrogen dioxide and fine particulate matter—they found that ozone had a particularly strong impact. The risk of asthma was higher when ozone levels were above 25 parts per billion, regardless of nitrogen dioxide levels. Interestingly, the connection between ozone and asthma was only evident when fine particulate matter was also present at or above average levels, suggesting a complex interaction between different pollutants.

The study calls for further investigation into why ozone exposure doesn’t seem to affect older children and whether the risk might return during adolescence. However, the results already point to a need for more comprehensive air quality regulations.

“In the United States, ozone regulations only consider a very short time period,” said Dearborn. “Maybe we should be considering both short- and long-term thresholds when regulating ozone, especially to protect children’s health.”

Get Latest News Live on Times Now along with Breaking News and Top Headlines from Health and around the world.