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. It was found that these men had 25% higher sperm concentration than the men who mostly wore tighter-fitting underwear and their total sperm count was 17% higher.
They sought to test the theory that briefs, being more constricting, raise scrotal temperature and have a negative effect on fertility.
"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. "There seems some compensation, but this compensation is not sufficient to bring them back to sperm counts of men who wear looser-fitting underwear".
Also, the study did not measure actual pregnancy outcomes, so it was unclear whether the differences in sperm count and quality uncovered actually made a bottom-line difference in the desired outcome. "And unless you're in a fertility clinic you don't know what your sperm count is".
You can also avoid damage to your balls - and your sperm as a result - by avoiding high temperatures such as in hot baths and hot tubs.
"It is a simple measure to wear boxer shorts when there is uncertainty regarding fertility", he commented.
In one of the largest studies of its kind, a team of researchers from the European Society of Human Reproduction and Embryology has analysed the link between what type of underwear a man wears and his semen quality. Each provided a semen and blood sample, and answered a questionnaire that asked about the type of underwear they most often wore during the preceding three months. While the locker-room debate among men - boxers vs briefs - is more aesthetic than medical, the question has always been raised: do tight-fitting shorts overheat the family jewels?
Other lifestyle activities of these men were also seen. "But if you're exercising and wearing tighter underwear, you're probably putting your testicles at risk for heat".
Men who wore boxers also had higher percentages of motile sperm or sperm that are capable of moving through the female reproductive system and fertilizing an egg.
However, other experts said they wouldn't make a flat-out recommendation for men to switch to boxers. Hence despite having poorer quality of sperms, these men had high levels of FSH. "This was reflected both in sperm concentration as well as in total sperm count".
The findings suggest that this hormone kicks into gear when it needs to compensate for increasing scrotal temperatures and decreasing sperm counts in tight underwear.