Air quality is linked to a wide range of health problems, including respiratory problems, cardiovascular complications and cancer, and that list of concerns continues to grow. According to researchers presenting this week at the 42nd Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE), common contaminants may be fundamentally altering the genetics of human sperm, and these alterations may affect much more than male fertility.

The project, one of the largest studies of its kind, was conducted from 2013 to 2017 and included more than 2,000 men in Salt Lake City, Utah. Volunteers provided researchers with semen samples initially after signing up, and then at intervals of two, four and six months. The researchers particularly focused on examining changes in sperm DNA methylation. These chemical changes regulate genetic activity without actually rewriting the DNA itself. Changes in methylation are already linked to genes used during chromosome organization, cell maintenance, and overall sperm development.

At the same time, the team also used regional data to estimate men’s exposure to outdoor air pollutants during the roughly three-month period of sperm production known as spermatogenesis. These included common concerns such as nitrogen dioxide, sulfur dioxide, fine particulate matter and ozone. Although previous studies have already uncovered evidence linking air pollution to semen quality, geneticists still do not fully understand how these adverse outcomes occur at the molecular level.

The researchers noted that ozone and nitrogen dioxide are among the most influential pollutants. Torque is frequently recorded at higher levels in urban areas such as Salt Lake City due to natural gas combustion and traffic emissions.

“Our findings suggest that exposure to air pollution during key stages of sperm development may be associated with changes in sperm DNA methylation, including genes involved in spermatogenesis and early developmental processes,” Carrie Nobles, study co-author and environmental health scientist at the University of Massachusetts Amherst, said in an accompanying statement.

Researchers identified 39 DNA methylation changes associated with air pollution, especially in GNAS—An imprinted gene linked to poorer semen quality and fetal development. However, Nobles explained the GNAS The implications are “particularly important.”

“Because imprinted genes can persist during early embryonic development, this raises important questions about whether parental environmental exposure can influence not only fertility, but also pregnancy and offspring health,” he said.

Since these are preliminary findings, Nobles emphasized that it is vital that researchers work now to replicate their results in future studies. He also explained that more research is needed on the measurable effects on men’s fertility and pregnancies, as well as other sources of pollution.

“We know that couples exposed to air pollution often have difficulty getting pregnant, and this may be one explanation among the countless ways pollution affects our reproductive health,” former ESHRE president Karen Sermon said of the study.

2025 PopSci Best of what’s new

The 50 most important innovations of the year