Summary
This review summarizes current evidence showing that elevated testicular temperature can impair spermatogenesis, although the strength of supporting data varies across lifestyle and occupational exposures. While daytime scrotal temperatures rise with prolonged sitting and inversely correlate with semen quality, studies have not consistently confirmed that time spent sitting directly reduces fertility. Professional drivers—who experience long periods of seated heat exposure—often show impaired semen parameters, but confounding factors make interpretation difficult. Tight-fitting underwear reliably increases scrotal temperature, yet convincing evidence linking it to reduced semen quality is lacking. Findings on occupational heat exposure and sauna use remain inconsistent, offering no definitive conclusions. Conversely, men with varicocele exhibit chronically elevated scrotal temperatures and poorer semen quality, and several studies suggest that varicocelectomy can normalize temperature and improve fertility. Fever is also clearly associated with temporary declines in semen quality. Although deliberate genital heat stress has been explored as a contraceptive method, it produces inconsistent suppression of spermatogenesis and is unreliable. In contrast, targeted scrotal cooling has been shown to improve semen parameters. Overall, while heat stress can impair spermatogenesis, the robustness of evidence varies, and individual factors strongly influence outcomes.
PMID: 18076419
DOI: 10.1111/j.1439-0272.2007.00794
Abstract
The concept that an elevation of testicular temperature results in impairment of spermatogenesis is widely accepted. Here, current knowledge concerning genital heat stress and its consequences in men is reviewed. Duration of sitting during work positively correlates with daytime scrotal temperatures and daytime scrotal temperature negatively correlates with semen quality. However, the assumed negative correlation between duration of sitting and semen quality could not be shown in the available studies. Fertility parameters of professional drivers with long periods of sitting in vehicles were impaired; however, for predominantly affected drivers of vans, trucks or industrial heavy machinery potential confounders have to be considered. Wearing tight fitting compared with loose-fitting underwear is associated with significantly higher scrotal temperatures. However, available observations suggesting a link between tight-fitting underwear or trousers and impaired semen quality are not convincing. Studies addressing professional exposure to high temperatures delivered conflicting results concerning fertility parameters. The postulated negative impact of sauna visits on semen quality is not sufficiently underlined by the available studies. Oligozoospermic men with a varicocele have significantly higher scrotal temperatures than normozoospermic men, and according to several studies varicocelectomy normalises scrotal temperatures. A further link has been reported between fever and deteriorated semen quality. Contraception via genital heat stress has been demonstrated using hot sitting baths or insulating suspensors. However, down-regulation of spermatogenesis is inconsistent and unsafe. On the other hand, scrotal and consecutively testicular cooling is able to improve semen quality.
Jung A, Schuppe HC. Influence of genital heat stress on semen quality in humans. Andrologia. 2007 Dec;39(6):203-15. doi: 10.1111/j.1439-0272.2007.00794.x. PMID: 18076419.