A successful sperm entering an egg. 

A new study now confirms that men who wear boxers are more likely to have higher and healthier sperm counts that men who wear underwear that fits more snuggly on their scrotum. The study comes out of Harvard University and explains that researchers looked at semen samples from more than 600 men who were part of a couple seeking fertility treatment at the Massachusetts General Hospital in Boston. In addition to the samples, collected between 2000 to 2017, the men also disclosed various lifestyle habits, including what type of underwear they usually wore.

Fifty-three percent of the men typically wore boxers. And these men, the authors found, had a sperm concentration that was on average 25 percent higher than men who said they stuck to jockeys, briefs, or bikinis. They also had a total sperm count an average 17 percent higher, as well as more mobile sperm. And interestingly enough, the boxer men also had lower levels of follicle stimulating hormone (FSH), which helps regulate fertility. These differences were still apparent after accounting for factors like age or their level of physical activity.

The researchers theorize that FSH levels were higher in men who wore close-fitting underwear because their bodies were trying to compensate for the lower sperm count.

Author, Jorge Chavarro, an associate professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health explained that beyond providing additional evidence that underwear choices may impact fertility, the study provides evidence, for the first time, that a seemingly random lifestyle choice could have profound impacts on hormone production in men at both the level of the testis and the brain.

The study was published on Wednesday in the journal Human Reproduction.

“These results point to a relatively easy change that men can make when they and their partners are seeking to become pregnant.”- Lead author Lidia Mínguez-Alarcón