Sauna has one well-documented downside

Sperm production and testosterone synthesis require a narrow thermal window — 3 to 7°F below core body temperature. This is why the testes are anatomically positioned outside the body cavity, suspended in the scrotum with its own thermoregulation system (the pampiniform venous plexus).

A sauna session exceeds 176°F. That heat penetrates every exposed area of the body — including the one region engineered by evolution to stay cool.

When scrotal temperature rises even slightly, three biological processes are directly affected:

Spermatogenesis disruption — the production of new sperm cells is impaired at the cellular level. A temperature increase of just 1°C can reduce fertility by 14%, and a 2–3°C increase can halt sperm production entirely.

Leydig cell damage — these are the cells responsible for producing approximately 95% of a man's testosterone. They are highly sensitive to thermal stress, and sustained heat weakens their output.

HPG axis suppression — the hypothalamic-pituitary-gonadal axis is the hormonal signaling chain that tells the body to produce testosterone. Elevated scrotal heat disrupts this signaling, causing production to shut down.

The relationship between scrotal heat and male reproductive health is one of the most well-documented areas in andrology. Multiple peer-reviewed studies have established the connection:

The Garolla study is particularly significant because the exposure level — twice weekly — reflects a normal sauna routine, not extreme use. The damage was measurable, reproducible, and directly tied to sustained heat exposure in the groin area.

Additional research has shown that scrotal cooling can reverse these effects. Studies on men with varicocele-related infertility demonstrated that localized cooling improved sperm count, motility, and morphology — confirming that temperature regulation is a viable, non-invasive intervention.

The full spermatogenesis cycle takes approximately 74 days — meaning that one period of unprotected heat exposure can affect sperm quality for nearly three months.

This is no longer a fringe concern. Some of the most prominent figures in health optimization and longevity have publicly addressed the impact of sauna heat on male reproductive health.

Johnson's public sharing of his own semen analysis data — before and after implementing scrotal cooling during sauna — became one of the most-discussed data points in the biohacking community. His results showed that unprotected sauna use caused dramatic, measurable decline across every fertility metric.

Dr. Huberman has discussed scrotal thermoregulation extensively on his podcast, framing it as one of the most actionable and overlooked areas of male health optimization. His audience — millions of health-conscious men — now actively seeks solutions for thermal management during sauna.

Other voices contributing to this conversation include Dr. Rhonda Patrick (FoundMyFitness), who has covered the sauna paradox — the conflict between systemic health benefits and localized reproductive risk — and fertility specialists who increasingly recommend scrotal cooling as a first-line, non-invasive intervention.

The benefits of regular sauna use are extraordinary and well-documented:

Men who used the sauna 4–7 times per week had a 50% lower risk of cardiovascular mortality and a 66% lower risk of dementia. Sauna triggers heat shock protein activation, growth hormone release (up to a 16-fold increase), improved blood pressure, and accelerated recovery.

But that same heat — the heat that delivers all these benefits — simultaneously damages the one area of the male body that cannot tolerate it.

This is the sauna paradox. And until recently, men had to choose: take the heat and accept the reproductive cost, or avoid the sauna entirely.

CULMIN exists to eliminate that trade-off.

The principle behind CULMIN is simple and supported by research: localized scrotal cooling preserves the testes without lowering systemic core temperature. You still get the full cardiovascular, hormonal, and recovery benefits of sauna — while protecting the area that needs to stay cool.

Each pair of CULMIN boxer briefs includes two reusable BPA-free cooling inserts that sit in a discreet integrated pocket. Freeze, slide in, sauna. The cooling effect lasts through a full session.

No ice packs. No improvisation. No compromise. Just a more considered way to sauna.