Experts confirm that your choice of undies matters.

Your choice of underwear could affect a lot more than just your comfort level, according to a new study from researchers at Harvard.

They found that men who reported wearing looser styles of underwear, such as boxers, had higher sperm concentrations and total sperm count, as well as healthier sperm, than those who reported wearing briefs.

“[The study] does sit well with the fact that, biologically speaking, elevated scrotal temperature is not good for the sperm,” says Dr. Tomer Singer, assistant professor at Hofstra School of Medicine and director of reproductive endocrinology and fertility at Lenox Hill Hospital in Manhattan. “Sperm is a very unique cell in the body and high temperature can affect its motility, its quality, and it can affect its potential for fertilizing an egg.”

Researchers examined sperm samples from a group of nearly 700 men seeking fertility treatment at a fertility center between 2000 and 2017. The average age of men in the group was 35. The average BMI of the group was 26.3, meaning slightly overweight.

Men who reported wearing looser underwear had about 25 percent higher sperm concentrations and 17 percent higher total sperm count than those with tight underwear.

But before you go toss your favorite pair of jockeys in the trash, the study had several limitations that also need to be considered. Both BMI and age can affect sperm concentration and health.

On average the group that wore tighter underwear tended to be about one year older and had slightly higher BMI.

“I wouldn’t take one study like this and say you know this is the end of tight underwear for everyone that has infertility and everyone should wear loose underwear. It’s a study in the right direction,” said Singer, who is not affiliated with the study.

Doctors have previously pointed at underwear as a potential culprit for an ongoing decline in semen quality in men in western countries. According to the study authors, both sperm count and testosterone levels have been steadily decreasing in these populations during the 20th and 21st centuries.

Other lifestyle factors including smoking, alcohol, and certain medications are known to affect sperm count. Saunas, hot tubs, and even electric blankets, which all raise scrotal temperature, can also be deleterious for sperm count.

“I don’t want guys to get too nervous about it, but I do believe that there is some decline in the sperm parameters that we’ve seen in the past two decades — whether it’s because of cellular phones or less healthy diet or sedentary lifestyle — we do see a trend in worsening sperm parameters,” said Singer.

The study could also have significance for men who aren’t struggling with infertility as well.

“Poor semen quality has been also associated with higher risk of common chronic diseases highlighting their public health importance beyond fertility and reproduction. So not only men who are trying to conceive should pay attention to their semen quality,” Lidia Mínguez-Alarcón, PhD, research scientist at Harvard T.H. Chan School of Public Health and lead author of the paper, told Healthline.

There is still more work to be done, but the take-home message for most men is that you should at least be considerate of your underwear choice, especially if you’re dealing with infertility problems. Still, when it comes to modifying lifestyle factors, changing underwear probably isn’t the most important.

“I would encourage healthy lifestyle; encourage reduction in alcohol, smoking; I would recommend cutting down on medication that may have an impact on sperm quality before I would focus on the type of underwear that guys are wearing,” said Singer.