A hospital-based cross-sectional study of 116 Thai male partners seeking infertility care assessed underwear fit and one semen sample. Some associations appeared for semen volume and morphology, while other parameters did not differ; causation cannot be inferred.
Key findings
- During daytime, 93.1% wore tight-fitting underwear; 74.1% used boxers or none at night. Loose fit day and night was associated with 1.232 mL higher volume (95% CI 0.406-2.057; p=0.004), while tight fit day and night was associated with 0.491 units higher normal morphology (95% CI 0.044-0.937; p=0.031). Other semen measures were not significant.
Why this matters globally
The question is attractive because behavior is modifiable and inexpensive, but credible guidance requires longitudinal or randomized crossover evidence controlling heat, spermatogenic timing, and confounders rather than one questionnaire.
Thai researcher contribution
The Chulalongkorn University and King Chulalongkorn Memorial Hospital team generated Thai clinic-based data including conventional semen parameters and DNA fragmentation.
Limitations to consider
Cross-sectional, single-center infertility-clinic data rely on self-report and one sample. Only 6.9% wore loose underwear by day, increasing imprecision. Multiple outcomes raise chance-finding risk, and duration, heat, occupation, abstinence, and lifestyle may confound results.