If you’re packing a pair of testicles, you’ve likely heard that keeping your scrotum and its precious cargo from getting too overheated is essential for maintaining healthy sperm. This proven link between temperature and fertility is often the linchpin of pro-boxer arguments presented during debates with briefs wearers.

And now, a new study by Harvard TH Chan School of Public Health adds more fuel to the long-running underwear superiority war by confirming that tightly fitting gonad garments are associated with reduced sperm concentration and counts using the largest-ever cohort of reproductive age men. Though the physiological mechanisms behind this pattern remain mysterious, the authors also discovered that men who wore briefs, "jockeys" (tight but long undies), or 'bikinis" (tight and very short undies) had lower blood levels of follicle-stimulating hormone (FSH) – a chemical messenger involved in spermatogenesis that is produced in the brain’s pituitary gland.

"An important strength of this study is that we were able to investigate the potential relationship between the type of underwear worn and indicators of testicular function such as reproductive hormone levels and DNA damage, which were missing in all previous studies on the topic,” Dr Lidia Mínguez-Alarcón, first author of the study published in Human Reproduction, said in a statement. She and her colleagues note that numerous investigations have tried to directly connect temperature differences from types of underwear to reproductive health, but the results have been inconsistent.

“Because of this, we were able to find a potential compensatory mechanism whereby decreased sperm production relating to the type of underwear signals to the hypothalamus to increase secretion of gonadotropin[s], [hormones that act] on the testes and that is reflected by the increased levels of FSH, to try to increase sperm production.”