November 6, 2026, 7:41 pm | Read time: 2 minutes
A study involving nearly 27,000 men shows a link between tight underwear and poorer sperm quality. Notably, differences were observed in sperm shape and DNA damage. But what can really be inferred from this?
Whether briefs or boxers, for many men, it’s primarily a matter of comfort. But could the choice of underwear also be related to fertility? A new study from China provides some clues.1 Researchers examined data from 26,836 men who visited a clinic for fertility evaluation.
21,221 men reported wearing mostly loose-fitting underwear. 5,615 mostly wore tight-fitting styles, including briefs, thongs, or tight boxers. The researchers compared these reports with various semen quality characteristics, also considering other health factors.
Tight Underwear, Poorer Sperm Quality?
Compared to loose underwear, tight clothing was associated with an increased risk of significantly lower semen volume (by 18 percent) and motility (by 13 percent). The most pronounced effect was on sperm shape. The risk of having a lower proportion of normally shaped sperm was 48 percent higher. Importantly, the absolute differences between the groups were small, averaging 1 to 2 percentage points.
Interestingly, after accounting for other lifestyle factors, underwear had no statistically significant impact on the pure sperm count per milliliter.
The link with DNA fragmentation was particularly striking. This measure describes how often the genetic material in sperm is damaged. Men wearing tight underwear had more than double the statistical likelihood of an increased value compared to those wearing loose underwear.
What Role Does Temperature Play for Sperm?
One possible explanation is heat development. The testes are located outside the body because sperm require a slightly lower temperature than the body’s core temperature for development. Tight-fitting underwear could restrict ventilation and increase the temperature in the scrotum. However, this study did not prove that this mechanism explains the observed differences.
Therefore, it’s important to put this into context: The study shows a statistical correlation, but not proof of cause and effect. Additionally, only men who sought medical evaluation for fertility were considered. The results cannot be readily generalized to all men.
Whether loose underwear actually improves the chances of pregnancy is also uncertain. Those hoping to conceive might consider wearing comfortably fitting, less tight underwear as a simple adjustment. However, it is not a guarantee of better sperm quality or pregnancy.