Wearing tight underwear is associated with reduced sperm count, according to a recent study which was led by researchers from the Harvard T. H. Chan School of Public Health, and published in Human Reproduction.
In this cross-sectional study, semen samples were analyzed from 656 male partners of couples seeking infertility treatment at a treatment centre from 2000-2017, to assess the effect of underwear choice on sperm quantity.
Boxer-wearing men had a 25% higher sperm concentration than those who reported not wearing boxers. Boxer-wearing men also had a higher total sperm count, and lower serum concentration of follicle-stimulating hormone, FSH.
Elevated scrotal temperatures are known to negatively affect testicular function. There's an adaptive reason which explains why human males evolved with testicles external to the abdomen. Sperm cells lose their mobility and viability at 37 degrees Celsius, so keeping them external to the abdomen allows them to stay cooler.
Despite this, studies on underwear choice and its relation with scrotal temperature and male testicular function have been inconsistent. In 1998, a small study consisting of 97 men was published in the Journal of Urology, where the authors claimed that the hyperthermic effect of brief style underwear had been exaggerated, and concluded that routinely advising infertility patients to wear boxer shorts was not justified.
However, authors of the current study persevered with the age-old question, and completed the research with a much larger study group.
Although this study was not designed to directly measure fertility, these results do suggest an easy way for men to help their chances of improving their fertility.
An andrology researcher from the University of Sheffield, Professor Pacey (who was not involved in the study), shared his thoughts with the BBC:
“Potentially switching from tight to loose might help some men who are on the lower edge of sperm production.”
The authors concluded that certain styles of male underwear may impair spermatogenesis, which may result in a compensatory increase in gonadotrophin secretion, as reflected by a higher serum FSH concentration in men who frequently wore tight underwear.
The authors acknowledged several limitations of the study. Underwear use was self-reported in a questionnaire, so misclassifications were possible. Blood sampling was not limited to the morning, so circadian variation in hormone levels was not accounted for. Other potentially confounding factors that were not taken into consideration included the type of trousers worn, and the textile fabric of the underwear.
Regardless, there are some harmless implications of the findings, as outlined by Professor Pacey:
"It shows that tight pants have an effect and shows there is a relatively cheap and easy thing that men can attempt to do to try and improve their situation."
The paper's author, Dr Jorge Chaverro, told the BBC: "It takes about three months for an entire population of sperm to change, so plan in advance.”
“Infertility is most certainly not just a female problem. Reproduction is a team sport. You need both people to make a baby. I think we still have a lot to learn about men's contribution to fertility."
Mínguez-Alarcón, L., Gaskins, A. J., Chiu, Y., Messerlian, C., Williams, P. L., Ford, J. B., . . . Chavarro, J. E. (2018). Type of underwear worn and markers of testicular function among men attending a fertility center. Human Reproduction. doi:10.1093/humrep/dey259