Are Tighty-Whities Bad for a Man's Sperm Count?

Men's underwear hanging from a clothesline.
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For men, deciding between boxers and briefs may be about more than just comfort — men's underwear choices may affect their sperm health, a new study suggests.

The study, which included more than 600 men, found that those who wore boxers had higher sperm counts than those who wore tighter underwear, such as briefs or jockeys.

The findings suggested that tight underwear may impair sperm production, the researchers wrote in the study, published today (Aug. 8) in the journal Human Reproduction.

However, the study didn't look at the effect of switching underwear styles on sperm count, nor did it examine whether men who wear tight underwear had lower chances of conceiving a child. [Trying to Conceive: 12 Tips for Men]

While experts praised the study's concept, they also noted that low sperm counts don't always mean low fertility, especially since sperm counts are highly variable.

A "man's sperm counts can vary tremendously week to week," said Dr. Sarah Vij, a urologist at the Cleveland Clinic who was not involved with the study. Vij acknowledged that many studies of male fertility use sperm counts because they are much easier to study than pregnancy rates. But even if a study finds that something is linked with lower sperm counts, "does that actually translate to a lower ability to cause a pregnancy?" Vij said. "We always struggle in our field to make that leap."

Boxers or briefs?

It's known that higher testicular temperatures can negatively affect sperm production. Tighter underwear could potentially lead to higher testicular temperatures, by holding the testicles closer to the body, but studies looking at the effect of underwear style on testicular function have had inconsistent results.

The new study is one of the largest to examine the link between underwear type and sperm quality. It involved 656 men, mostly in their 30s, who visited Massachusetts General Hospital for infertility treatment with their female partners between 2000 to 2017.

The men provided semen and blood samples and answered questions about the type of underwear they wore most frequently. Overall, 53 percent of men said they usually wore boxers. [Should You Wear Underwear to Bed?]

Both men who wore boxers and men who wore tighter underwear had average sperm concentrations that were "normal"; that is, they had at least 15 million sperm per milliliter of semen.

But men who wore boxers had 25 percent higher sperm concentrations, and 33 percent more swimming sperm in a single ejaculate, on average, than men who wore tighter underwear. The findings held even after the researchers took into account factors that can affect sperm health, including obesity, physical activity, frequent hot baths and smoking.

What's more, the researchers found that men who wore tighter underwear had higher levels of a hormone called follicle stimulating hormone (FSH), which stimulates sperm production.

That finding suggests that, in men who wear tighter underwear, decreased sperm production may send a signal to the brain to increase levels of FSH to compensate for the lower sperm production. But more studies are needed to confirm this hypothesis.

Should men switch?

The researchers said that the findings provide some simple advice to men looking to conceive. "These results point to a relatively easy change that men can make when they and their partners are seeking to become pregnant," lead study author Lidia Mínguez-Alarcón, a research scientist at the Harvard T. H. Chan School of Public Health, said in a statement.

However, other experts said they wouldn't make a flat-out recommendation for men to switch to boxers.

Vij said she "applauded" the study question, but "I don't know that I would recommend [switching] based on this study." When men have trouble conceiving, "we hope that there are other ways that we can intervene that have a little more significant science and data to back them up," she said.

Dr. Michael Eisenberg, director of male reproductive medicine and surgery at Stanford University School of Medicine, agreed. "I generally counsel men that they can choose the type of underwear that is most comfortable," Eisenberg told Live Science. "But if they do feel warm or constricted, then another type may make sense," he added.

Still, Eisenberg said that "if the current study can be consistently reproduced, then I think it's something we should discuss with all patients." In 2016, Eisenberg co-authored a study of 500 men that found that, no matter what type of underwear the men wore, the time it took couples to become pregnant was about the same.

It's also important to note that the study wasn't able to consider some factors that could affect testicular temperatures, such as the type of underwear fabric, or whether the men wore tight pants such as skinny jeans, the researchers said.

Eisenberg said that if men are having trouble conceiving, they should see a doctor for an evaluation of risk factors for fertility problems.

Original article on Live Science.