Sauna exposure and human spermatogenesis: heat effects on sperm parameters

Objective: To assess whether repeated sauna exposure affects human spermatogenesis and sperm quality. Healthy men underwent a defined period of regular sauna bathing, with semen analyses and reproductive hormone measurements obtained before, during, and after the heat exposure phase. Repeated sauna use was associated with declines in sperm concentration, motility, and morphology in several participants, indicating heat-related impairment of spermatogenic function. Importantly, the changes appeared at least partially reversible after cessation of sauna exposure, supporting a direct thermal effect rather than permanent damage. Hormonal measures were less consistently altered, suggesting that the principal mechanism may involve local testicular heat stress. The study provided concrete human evidence that frequent high-temperature exposure can transiently compromise male fertility parameters. Although the sample was small and the protocol specific, the findings have practical implications for counseling men with fertility concerns, especially those with other sources of heat exposure or reduced baseline sperm reserve.