Air pollution may be doing more than irritating the lungs and heart. New research suggests it could also leave tiny chemical marks on genes involved in sperm development, potentially influencing not only a man's fertility but also the health of future children.

The findings, presented at the 42nd Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE), come from one of the largest studies to examine how everyday air pollution may affect sperm at the molecular level. The study abstract is being published in Human Reproduction, a leading journal in reproductive medicine.

Researchers analysed data from more than 2,000 men in Salt Lake City, Utah, who took part between 2013 and 2017. Participants provided semen samples when they joined the study and again after two, four and six months. Scientists examined DNA from 1,220 men who completed the six-month follow-up, focusing on DNA methylation—tiny chemical tags that switch genes on or off without changing the genetic code itself.

The team estimated exposure during spermatogenesis, the roughly three-month period when new sperm are produced. They assessed common pollutants, including ozone, nitrogen dioxide, sulphur dioxide and fine particulate matter (PM2.5), which are microscopic particles small enough to enter the bloodstream.

After months of laboratory analysis, researchers identified 39 DNA methylation changes linked to mixtures of air pollutants. Ozone and nitrogen dioxide, both commonly associated with traffic emissions and natural gas combustion, appeared to contribute most strongly.

Among the most notable findings was altered activity in GNAS, an imprinted gene whose behaviour depends on whether it is inherited from the mother or the father. Previous research has linked this gene with semen quality and early embryo development, making it a potential biological bridge between a father's environmental exposure and pregnancy outcomes.

Lead author Dr Carrie Nobles said, “Our findings suggest that being exposed to air pollution during important times of sperm development may be linked to changes in sperm DNA methylation, including in genes related to sperm production and early development.”

She added, “The association with changes in the imprinted gene GNAS was particularly important. Because imprinted genes can persist through early embryonic development, the findings raise important questions about whether fathers’ environmental exposures may influence not only fertility but also pregnancy and offspring health.”

Dr Nobles cautioned that air pollution is a complex mixture that varies with season and location and stressed that the study shows an association rather than proving that pollution directly causes these genetic changes. “A critical next step is replication of findings in other studies,” she said, adding that researchers also need to investigate whether these molecular changes translate into measurable effects on fertility, pregnancy and children's health.

The findings build on earlier evidence from the World Health Organization, The Lancet, Environmental Health Perspectives and Human Reproduction, which has linked long-term air pollution with poorer semen quality, pregnancy complications, cardiovascular disease and respiratory illness. The new study offers one possible biological explanation for those observations.

Commenting independently, Professor Dr Karen Sermon, immediate past chair of ESHRE, said, “This new study is another piece of the puzzle to understand how pollution negatively influences our fertility. We know that couples exposed to air pollution often have difficulties becoming pregnant, and this may be one of the explanations among the myriad ways that pollution impacts our reproductive health. the myriad ways that pollution impacts our reproductive health.”

As scientists continue to unravel how polluted air affects the body, the research adds to growing evidence that cleaner air may be important not only for healthier lungs but also for healthier families yet to be born.