Garment fit, scrotal thermoregulation, and male fertility outcomes: a narrative review

Scrotal thermoregulation is a recognized feature of normal spermatogenesis, with testicular function occurring at temperatures below core body temperature. Tight-fitting underwear has been hypothesized to influence scrotal temperature, whereas looser garments may allow greater ventilation. Public interest in "fertility-friendly" underwear has increased despite uncertainty regarding clinical relevance. This narrative review synthesizes current literature examining associations between underwear choice, particularly garment fit and fabric, and semen parameters and male fertility outcomes.

A structured literature search of PubMed up to April 20th, 2025 was conducted using keywords related to underwear type ("underwear", "boxers", "briefs", "undergarments"), scrotal temperature ("scrotal temperature", "testicular temperature"), and male fertility ("male fertility", "sperm quality", "semen parameters", "sperm concentration", "sperm motility", "sperm morphology", "fecundity"). Peer-reviewed human studies published in English evaluating underwear fit or fabric in relation to semen parameters, reproductive hormones, or fertility outcomes were included. Experimental studies involving testicular heat exposure were reviewed to provide physiologic context. Data were synthesized qualitatively.

Physiologic studies have reported higher scrotal temperatures associated with tighter underwear. Observational studies have described modest differences in semen parameters between men wearing briefs and boxers, while prospective data have not demonstrated differences in pregnancy outcomes. Cross-sectional analyses have reported differences in sperm concentration and follicle-stimulating hormone levels by underwear type. Evidence regarding fabric composition remains limited, and controlled human studies comparing materials under typical wearing conditions are lacking.

Underwear choice has been variably associated with modest differences in sperm production parameters, although findings are inconsistent and clinical fertility outcomes have not demonstrated clear associations. Evidence regarding fabric composition remains limited. In clinical discussions, avoidance of excessive scrotal heat exposure may be considered as a general measure, while emphasizing that underwear choice alone is unlikely to meaningfully influence fertility outcomes for men.