Should you be getting get your knickers in a twist over the “right” underwear to wear?

There’s long been debate over whether boxers or briefs are better for your manhood — and sperm quality.

But a new study of 27,000 aims to settle this debate about drawers once and for all.

Chinese researchers found that snug undergarments can prove detrimental to sex — and not just cause they’re allegedly a massive turnoff. They could potentially impact men’s performance in the sack, too.

“Tight underwear was associated with poorer semen quality and a higher prevalence of erectile dysfunction and premature ejaculation,” wrote the authors, led by urologist Xue-Chun Hu from the University of Science and Technology of China (USTC), in the Asian Journal of Andrology.

Bulge-hugging briefs have been linked to poor male reproductive health for years, with even sperm banks recommending boxers for better sperm counts, and in theory, better fertility.

But large-scale evidence remained limited — until now.

To see whether form followed dysfunction in underwear, the researchers recruited 27,000 male participants, making this the largest study of its kind, Science Alert reported.

They then compared the semen quality of those who rocked loose boxers with their tighty-whitey-wearing counterparts, making sure to factor in habits such as smoking and drinking along with any preexisting conditions.

They found that, by and large, the sperm donors who wore tighter underwear generally produced less baby batter — and of poorer quality.

Those with more closely-skimming skivvies also boasted 108% higher odds of having more sperm with DNA fragmentation or damage. A second examination revealed that erectile dysfunction and premature ejaculation were also more common among the snug underwear group.

In addition, “prolonged use” of tight underwear “can reduce testosterone secretion and lead to sexual dysfunction,” they wrote, concluding that selecting looser, more billowy undergarments can help “protect semen quality and sexual function.”

When sperm get hot and bothered

Why are snug undies so bad for men’s sexual health? The idea is that the testes shouldn’t be … well, hot as balls.

For optimal sperm production, the testicles should be about 3.5 to 7 degrees Fahrenheit lower than the core body temperature. In theory, breezier boxers are better equipped to keep things comfortably cool.

Researchers of the new study noted that, compared with looser underwear, “tight briefs increase the temperature inside the scrotum by 0.5°C–1°C (0.9 to 1.8 F).”

Loading up on research

The new research follows a landmark 2018 study in which Harvard researchers took semen samples from 656 male partners of couples seeking infertility treatment. They found that men who wore boxers had 25% higher sperm concentration and 17% higher total sperm count.

Yet the authors only looked at men who were seeking fertility treatment with their partners, so it remained possible the findings didn’t apply to the general population.

They also emphasized that they don’t know whether underwear choice causes lower or higher sperm count. There could be a number of other things that could mess with the temperature down there, including the fabric and type of pants.

But not every study has come to the same conclusion. One out of Thailand, published in July, found there was no difference in sperm count between those wearing tight vs. looser underwear.

They also found that while semen volume was higher in men wearing loose fitting underwear, the size and shape of sperm was better in those wearing tight fitting underwear.

A review published in May might be even more damning: It didn’t find any difference in pregnancy outcomes between those who wore tight vs. looser underwear.

“Findings are inconsistent and clinical fertility outcomes have not demonstrated clear associations,” the authors wrote. “Underwear choice alone is unlikely to meaningfully influence fertility outcomes for men.”

What they found was that yes, tighter underwear was associated with higher temperatures. And while some studies, like that 2018 study, showed higher sperm count among those wearing boxers, data on sperm quality was inconsistent, and pregnancy outcomes didn’t show a clear difference.