A recent review published in Translational Andrology and Urology on June 17 finds that while looser underwear may help keep testes cooler and support some sperm measures, the evidence does not prove it can increase a man's chances of fatherhood.
Researchers conducted a structured narrative review examining whether underwear fit and fabric characteristics are associated with scrotal temperature, semen quality, reproductive hormones, and male fertility outcomes. The authors searched PubMed for studies published up to April 20, 2025, focusing on types of underwear, scrotal or testicular temperature, sperm quality, semen quality, and fertility outcomes. Only peer-reviewed studies involving human participants were included.
The reviewed evidence showed that tight-fitting underwear increases testicular temperature by about 1°C compared with loose-fitting options or no undergarments. Some induced-heating models indicated that sustained increases in testicular temperature could negatively affect spermatogenesis. However, findings comparing boxer shorts and briefs were inconsistent; several early studies found no meaningful differences in sperm concentration or motility between men wearing loose or tight underwear. Other research suggested that tight clothing may increase the risk of abnormal semen quality when combined with tight trousers.
More recent observational studies have reported associations between looser underwear and better semen measures such as higher sperm concentration and lower DNA damage. For example, one cross-sectional study of over 650 men attending a fertility center found boxer-short users had approximately 25% higher sperm concentration than those who wore tighter underwear. Despite these laboratory findings suggesting physiological benefits from looser garments, there was little consistent evidence showing an impact on real-world fertility outcomes such as conception delay or infertility rates.
The review also examined fabric composition but found little information comparing natural versus synthetic fabrics under normal conditions. Textile studies suggest cotton-containing fabrics may release heat more effectively than polyester-based ones; however, there are no direct human fertility studies comparing these materials.
The authors concluded that while choice of underwear may modestly influence male reproductive physiology by altering scrotal temperature—and some studies indicate slightly higher sperm production among men wearing loose-fitting garments—there is currently no consistent evidence showing improved semen parameters translate into better fertility outcomes. Underwear selection should be considered a supportive lifestyle factor rather than a proven intervention for improving male fertility.
