Heat, Warmth, and Sperm Quality
Testicles sit outside the body for a reason: spermatogenesis, the roughly 90-day process of sperm development, functions best a few degrees below core body temperature. A recurring theme across the research is that extended heat exposure - from saunas, hot tubs, and even laptops resting directly on the lap - is one of the more consistently documented lifestyle factors linked to lower sperm counts and motility.
Saunas and direct heat
A 2013 study published in Human Reproduction followed Finnish men who used a sauna for 15 minutes, twice a week, for three months.1 Scrotal temperature rose by roughly 3°C during sessions, and the researchers observed a significant, measurable impairment in both sperm count and motility. Encouragingly, the effect was reversible - sperm parameters returned toward baseline within about six months of stopping.
Hot tubs and “wet heat”
A separate study led by researchers at UC San Francisco looked at what happened when men who regularly used hot tubs stopped.2 Among 11 men who discontinued wet heat exposure for at least three months, just under half saw a favorable response - with total motile sperm counts increasing by an average of 491% in that group. It’s a small study, and not every participant responded, but it points in the same direction as the sauna research: heat-related effects on sperm appear to be largely reversible once the exposure stops.
Laptops and everyday heat
Heat exposure doesn’t have to come from a sauna. A widely cited Human Reproduction study measured scrotal temperature in 29 men using a laptop directly on the lap and found it rose by a median of 2.6–2.8°C - with roughly a third of that increase (about 2.1°C) coming just from sitting with the thighs held together to balance the device, before the laptop was even switched on.3 Researchers have linked scrotal temperature increases of even 1°C to potential effects on sperm production.
A low-effort adjustment, not a guarantee
None of this means an occasional sauna session or a laptop left on a desk instead of a lap will make or break anything on its own - the research is about patterns of repeated, extended exposure, not one-off events. But of all the lifestyle factors researchers have studied, heat is one of the more consistent and directly modifiable ones. It’s also part of why daily reproductive-health routines, including Motility Boost, are typically framed around a similar ~90-day cycle - that’s roughly how long the studies above needed to see a measurable change, for better or worse.
These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.
Sources
- Garolla A, et al. “Seminal and molecular evidence that sauna exposure affects human spermatogenesis.” Human Reproduction, 2013;28(4):877–885. pubmed.ncbi.nlm.nih.gov/23411620
- Tarapore PE, Turek PJ, et al. “Wet heat exposure: a potentially reversible cause of low semen quality in infertile men.” International Braz J Urol, 2007;33(1). ucsf.edu coverage
- Sheynkin Y, et al. “Increase in scrotal temperature in laptop computer users.” Human Reproduction, 2005;20(2):452–458. pubmed.ncbi.nlm.nih.gov/15591087