Boxers or Briefs? Scientists Investigate How Men’s Underwear May Affect Sexual Health

Men concerned about their reproductive health may want to take another look inside their underwear drawers. A large-scale study involving 27,000 men has found an association between wearing tight-fitting underwear, poorer sperm quality and sexual dysfunction. However, researchers stress that whether loose-fitting boxers actually improve a man's chances of conceiving a child remains an open question.

Researchers from the University of Science and Technology of China compared sperm quality in men who preferred loose-fitting boxers with those who wore tight briefs. They also accounted for factors such as smoking, alcohol consumption and existing medical conditions.

The results showed that men who wore tighter underwear tended to have poorer sperm quality. They were also 108% more likely to have elevated sperm DNA fragmentation — damage to the genetic material carried by sperm. Erectile dysfunction and premature ejaculation were also more common in this group.

“Wearing tight underwear was associated with poorer semen quality, as well as a higher prevalence of erectile dysfunction and premature ejaculation,” the study, published in the Asian Journal of Andrology, stated.

The researchers suggest that one possible explanation is an increase in scrotal temperature. For normal sperm production, the testes need to remain approximately 3.5–7 degrees Fahrenheit cooler than core body temperature. According to the study, tight briefs can raise the temperature inside the scrotum by 0.5–1 degree Celsius compared with loose-fitting underwear.

Previous research has also suggested potential benefits of wearing boxers. In 2018, Harvard University researchers examined sperm samples from 656 men whose partners were undergoing fertility treatment. Men who preferred boxers had 25% higher sperm concentrations and 17% higher total sperm counts.

However, scientists are not yet drawing definitive conclusions. A study published in Thailand in July found no difference in sperm counts between men who wore tight and loose underwear. Men who preferred looser styles had a higher semen volume, while those wearing tighter underwear had better sperm size and shape measurements.

An even more cautious assessment came from a scientific review published in May. Its authors found no convincing evidence of a link between underwear type and the likelihood of achieving pregnancy.

“Research findings are inconsistent, and clinical evidence does not support a clear relationship between underwear choice and pregnancy outcomes. Underwear choice alone is unlikely to have a substantial impact on male fertility,” the researchers concluded.

In other words, loose-fitting underwear may help keep the testes cooler, and some studies have linked it to better sperm quality. But it is still too early to consider boxers a guarantee of good male reproductive health.