What the research says — and where it stops
We sell textiles, not medicine. Here is the evidence we build on, without exaggeration.
Heat and sperm production
Testicles sit outside the body for a reason: sperm production happens a few degrees below core temperature. That heat exposure affects sperm production is well established in the literature.
The most cited sauna study had ten men sit for 15 minutes, twice a week, for three months. Sperm count and motility dropped measurably, and values recovered only after roughly six months. The study is small — ten people — but the direction is consistent with the broader heat literature.
Cooling — promising, thin evidence
There is research on scrotal cooling, including nightly cooling in men with impaired semen quality and cooling-patch studies. Results point in the right direction, but the studies are small and the evidence base is limited.
There are no good studies on exactly what we do: an ice pack in the sauna. We are not going to pretend otherwise.
The Bryan Johnson angle
Bryan Johnson (Blueprint) runs daily dry sauna with an ice pack in the groin as stated protection, and has reported improved values in his own comparison of sessions with and without ice.
That is a self-experiment on one person, n=1, with no control group. We use it as a cultural reference — that the question is real — never as scientific proof.
Background
A large meta-analysis (Levine et al., 2022) reported that sperm concentration in population data fell by more than 50 percent between 1973 and 2018. That is context, not a product argument.
Our position
- We know heat affects sperm production. That is well established.
- We know cooling has shown promising results in studies, but the evidence base is small.
- We do not know whether our product improves anyone's fertility — and we are not going to claim it does.
- What we do is simple: we keep one area cooler while the rest of you gets hot. What you do with that information is up to you.
The hype: Bryan Johnson and the ice
The heat-cold-sperm question went from niche forums to tabloids when Bryan Johnson (Blueprint) started sitting in the sauna with an ice pack in his groin and publishing his own numbers. We don't use that as proof — we show you where it comes from and let you read on.
Clip from Bryan Johnson's channel on fertility. His ice-in-the-sauna protocol is a self-experiment, n=1, no control group — interesting, not evidence.
Sources (peer-reviewed)
- 1. Garolla A. et al. — Seminal and molecular evidence that sauna exposure affects human spermatogenesis. Human Reproduction, 2013.
- 2. Levine H. et al. — Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update, 2023.
- 3. Jung A., Schuppe H-C. — Influence of genital heat stress on semen quality in humans. Andrologia, 2007.
- 4. Osman M. W. et al. — FertilMate™ scrotum cooling patch and male fertility (SCOP), randomised trial. Trials, 2012.
Blue Balls Co. sells textile and comfort products. Our products are not medical devices and are not intended to diagnose, treat, cure or prevent any disease or condition. We make no claims about effects on fertility. Consult a doctor with questions about reproductive health.