In Brief: Boxers!
Although the link between the type of men’s underwear and fertility has been regarded by many as an old wives’ tale, folklore, or urban legend, the largest study to date has concluded that men who wear looser-fitting (boxer) shorts have higher sperm concentrations than men who wear tighter undergarments. The investigation, conducted by Dr. Lidia Mínguez-Alarcón and colleagues at the Harvard School of Public Health, studied 656 men in the Massachusetts General Hospital (Harvard) infertility clinic and not only looked at semen concentration but reproductive hormones and sperm DNA damage.
Recently published in the journal Human Reproduction, the researchers also found that men who wear boxers had lower levels of follicle-stimulating hormone, FSH, compared to men who most frequently tight-fitting underwear. (FSH is the pituitary hormone that stimulates sperm production.) These findings certainly suggest that FSH is elevated to compensate for the damage from increasing temperatures within the scrotum and decreasing sperm concentration.
Men who wore boxer shorts (53% of the study population) had a 25% higher sperm concentration, 17% higher total sperm count, 33% more swimming sperm in a single ejaculate and 14% lower FSH levels than men who did not usually wear boxers. All of these differences were statistically significant, even after adjusting for potentially confounding variables, such as body mass index, physical activity, hot baths and Jacuzzis, tobacco usage and the year the sample was taken.
There were no significant differences in other reproductive hormones or damage to the DNA of the sperm.
It is important to note that it is not possible to prove from this study that the type of underwear causes the difference in semen quality and FSH levels, only that that there is a strong association between them. Definitive proof is not possible from this study because other factors that might affect scrotal heat, such as the material and fit of trousers worn and underwear fabric type, could also affect the results.
Dr. Mínguez-Alarcón suggested, "Since men can modify the type of underwear they choose to wear, these results may be useful to improve men's testicular function."
- Lidia Mínguez-Alarcón, Audrey J Gaskins, Yu-Han Chiu, Carmen Messerlian, Paige L Williams, Jennifer B Ford, Irene Souter, Russ Hauser, Jorge E Chavarro. Type of underwear worn and markers of testicular function among men attending a fertility center. Human Reproduction, 2018; DOI: 10.1093/humrep/dey259