Air pollution may alter how sperm functions, study finds… and it can have a devastating impact on babies
One of the largest fertility studies of its kind has found that air pollution changes the way sperm genes work.
Men exposed to common air pollution while sperm are developing have seen subtle DNA changes that affect how genes are turned on and off, raising new concerns that air pollution could harm male fertility and the health of their offspring.
The findings, presented at the annual meeting of the European Society for Human Reproduction and Embryology in London, identified ozone and nitrogen dioxide as the pollutants most strongly linked to these changes.
The study followed more than 2,000 men in Salt Lake City, Utah, between 2013 and 2017. Participants provided semen samples when they enrolled and again two, four and six months later.
The researchers estimated each man’s exposure to outdoor air pollutants, including ozone, nitrogen dioxide, sulfur dioxide and fine particulate matter, during the three months before each sample, the period of sperm production.
Evidence that air pollution affects sperm health and may reduce male fertility has been growing for years, but the biological mechanisms remain unclear.
Most research has focused on the effects of pollution on sperm DNA fragmentation; This means damage to the DNA strands inside sperm cells, as well as sperm shape and movement.
But the latest study points to a different mechanism: DNA methylation.
Men exposed to common air pollution while developing sperm showed subtle DNA changes affecting their genes (stock image)
A major fertility study suggests air pollution may harm male fertility by altering DNA methylation (chemical tags that act like dimmer switches on genes in sperm cells), offering a potential biological pathway for the first time.
DNA methylation is a process in which chemical tags bind to DNA and act like dimmer switches, turning genes up or down without altering the underlying genetic code, one possible explanation suggests.
Most of these tags are deleted early in embryo development, but a small number of genes are ‘imprinted’, meaning they retain these marks and carry them forward, giving them the potential to influence the development of embryos and beyond.
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The scientists analyzed sperm DNA methylation in 1,220 men who provided samples at a six-month follow-up. They identified 39 DNA changes linked to air pollution mixtures; Ozone and nitrogen dioxide appeared to have the strongest effect.
One of the genes identified, GNAS, was previously thought to be linked to poor semen quality and fetal development.
Studies have found that when the paternal copy of GNAS is altered, it can lead to severe intrauterine growth restriction (IUGR), meaning the baby is born significantly smaller than expected for gestational age.
IUGR, also called fetal growth restriction, increases the risk of stillbirth, premature birth, brain damage, hypothermia, low blood sugar, and numerous lifelong health complications that can result from these conditions.
Epidemiologist and study leader Dr. from the University of Massachusetts Amherst. “Since imprinted genes can persist throughout early embryonic development, this raises important questions about whether fathers’ environmental exposures may affect not only fertility but also pregnancy and offspring health,” Carrie Nobles said.
He added that air pollution is a complex mix that varies by season and location.
About 152 million Americans, nearly half the country, live in places that receive failing grades for unhealthy levels of ozone or particle pollution, according to the American Lung Association’s 2026 State of Weather report.
Pollution levels change with weather conditions. For example, ozone tends to be higher on hot, sunny days because sunlight and heat help create it. Pollutants such as particulate matter from heating may be more prevalent during the winter months.
A rural agricultural area has a different pollutant profile than a city centre, where nitrogen dioxide from heavy traffic is a constant concern. Cities are particularly prone to high levels of nitrogen dioxide and ozone.
About 152 million Americans, nearly half the country, live in places that receive failing grades for unhealthy levels of ozone or particle pollution. The image above shows wildfire smoke pollution in Philadelphia in 2023.
Nitrogen dioxide is largely a byproduct of vehicle exhaust and the combustion of fossil fuels. However, ozone is not released directly, it is formed when other pollutants react with sunlight.
Cities obtain most of these raw materials, primarily from traffic and the burning of natural gas used for heating, cooking, and energy production.
The next critical step is to replicate the findings in other studies and investigate whether the DNA changes have measurable effects on fertility and pregnancy outcomes, Nobles said.
Karen Sermon, former president of the European Society for Human Reproduction and Embryology, said: ‘This is another piece of the puzzle to understanding how pollution negatively affects our fertility.
‘We know that couples exposed to air pollution often have difficulty conceiving, and this may be one explanation among the countless ways pollution affects our reproductive health.’
