Study Reveals Even ‘Acceptable’ Air Pollution Levels Can Threaten Male Fertility

That cleansing breath on a crisp fall day may be deceiving. Insidious and invisible, air pollutants can harm our bodies—all the way down to our gametes.

That’s the finding of a recent study that includes a University of Maryland researcher: Men’s exposure to even low levels of air pollutants can impair sperm development and damage male fertility.

“People tend to think air pollution affects really sick or elderly people, and that it’s all about asthma, COPD (chronic obstructive pulmonary disease) and other lung problems,” said Tim Canty of the Department of Atmospheric and Oceanic Science (AOSC). But air pollution is bad for the heart, can cause cancer, and it can also impact people’s ability to have a family—“even when the pollution is below the threshold that’s considered ‘safe’ by government standards.”

The study published in September in the journal Ecotoxicology and Environmental Safety found that exposure to ozone affected sperm morphology throughout spermatogenesis—the production of sperm in the testes—especially during the early and middle stages of the process. Late in sperm development, exposure to fine particulate matter like that found in vehicle exhaust was associated with lower sperm count and motility.

The findings add to a growing body of evidence that men’s exposure before conception to environmental hazards is an understudied contributor to couples’ inability to conceive, said the study’s lead author, Weill Cornell Medicine Postdoctoral Researcher Lindsey Russo, who studies links between the environment, reproduction and cardiovascular health. “These are real effects with real outcomes for families and human reproduction more broadly,” she said.

Infertility is common, affecting about one in six couples globally, with men contributing to half of those cases. The numbers are stark: In the United States average sperm counts are down 50% from 40 years ago. For millions of people without infertility insurance coverage, some treatments may be cost-prohibitive, running from $1,000 to $20,000 or more each cycle. 

The emotional burden of infertility is for some an even greater challenge than affording treatment. “You grow up expecting that building a family will happen naturally, so when it doesn’t, there can be depression, anxiety, anger and strain on the marriage,” said Dr. Stephanie Beall, a reproductive endocrinologist at Shady Grove Fertility Center as well as an adjunct professor and division director of Reproductive Endocrinology and Infertility at the University of Maryland School of Medicine, who was not involved in the study. 

The sheer numbers of people struggling to conceive continues to grow, she said. Infertility is usually caused by many factors coming together—some easily understandable like parents’ ages, others far less so. “We are exposed to so many things we weren’t 100 years ago,” Beall said. “Environmental exposure is a huge puzzle.”

How do harmful pollution exposures happen?

“Step outside, look around and take a deep breath,” Canty said. Noxious gases, ozone, particular matter and volatile organic compounds are all culprits—toxic stuff from cars and trucks, construction sites and power and industrial plants. Gas-powered leaf blowers and mowers pollute, as do cleaning supplies and paints. Fertilizers can pollute the soil and water, which then release those pollutants into the air. 

Even nature contributes, he said: Oak and poplar trees emit isoprene, which breaks down into other pollutants to worsen air quality. Volcanoes burp sulfur dioxide. Wildfires throw up smoke and particulates. The wind blows particulates around. Meanwhile, time, temperature and season can change pollutants’ activity and effects. 

Canty began working on a series of multidisciplinary projects that led to the sperm study after giving a talk on air pollution in Maryland to a small audience that included some of his current collaborators, including Pauline Mendola, now the department chair of epidemiology and environmental health at the University at Buffalo “Afterward, we all started talking about ways we might put our heads and data together to tackle important public health questions,” he said. 

For example, he provided pollution data for a study published in January that showed that late-pregnancy exposure to air pollutants negatively impacts birth outcomes, as measured by admissions to the neonatal care unit (NICU). 

“If you live along the I-95 corridor, in fact, it’s 30% more likely your child will visit the NICU because of [pre-birth] pollution exposure,” he said. “That’s a huge impact, not just health-wise but as an economic burden for people who may already be stretched thin.” 

A third environmental health study, published in Environmental Research Letters with Canty as co-author and Akanksha Singh Ph.D. ’26, a recent graduate from his research group, as first author, examines where to locate air quality monitors in communities for the best health outcomes. Excited to continue seeking answers together, he and collaborators have continued meeting regularly, brainstorming additional ways to bridge the gap between their diverse areas. 

“For us, that means bringing our air-quality knowledge and satellite observations and modeling to epidemiologists so they have the best available science to work with,” Canty said.

Next on researchers’ agenda: Assess the air quality impacts of data centers coming online as artificial intelligence expands the demand for computing power. 

“We’re trying to think, what does the future look like? And can we get ahead of some of these issues?” he said. Because when it comes to the air we breathe and its health implications, “there’s no such thing as ‘too clean.’”