Wearing boxers or other forms of loose underwear might result in higher semen quality than tighter styles, a new study suggests.
Published in Human Reproduction, the research compared men's semen quality with the style of underwear they wore, and found that regularly wearing boxer shorts correlated with higher sperm concentration. The finding supports current advice to men seeking fertility treatment in the UK to keep their testes cool by wearing loose-fitting underwear and avoiding hot baths.
Lead author Dr Lidia Mínguez-Alarcón from the Harvard T H Chan School of Public Health said: 'The results from this study are very practical. Men could improve their sperm production by easily changing their type of underwear.'
The 656 men included in the study were all partners of women attending Massachusetts General Hospital, Boston, USA, for fertility treatment between 2000 and 2017.
The men self-reported the type of underwear that they wore and provided blood and semen samples. Around half of the men usually wore boxers, and this group had on average 25 percent higher sperm concentration, 17 percent higher sperm count and 33 percent more motile sperm than men who preferred closer fitting styles.
The study also found that wearing tighter underwear, such as briefs, correlated with higher levels of follicle stimulating hormone (FSH), a hormone that stimulates sperm production.
Andrologist Professor Allan Pacey from the University of Sheffield, who was not involved in the study, said: 'This is an intriguing observation as it implies that the wearing of tight underwear may be damaging the testicles in some way, and is why the FSH levels from the pituitary rise to try and make the testicles work harder at producing sperm.'
An important limitation of this study is that the men self-reported the type of underwear that they wore and the frequency that they wore it. There is no explanation as to what 'frequently' means in terms of days per week.
Additionally, the researchers did not measure the temperature of the testes and used style of underwear to infer likelihood of higher scrotal temperatures.
Professor Sheena Lewis, emeritus professor of reproductive medicine at Queen's University Belfast, who was not involved in the study, said: 'The most important take-home message from this study is that neither boxer shorts, jockeys nor bikinis led to a drop in sperm counts below the normal range.'