Coldbrrr

The Science

Cold plunge and testosterone: the honest read

The internet says cold plunging raises testosterone. The literature is one rat study, one uneven human paper, and a lot of confident tweets. What the actual studies show, and what the popular claim is asking of them.

By Erik Lund ·

Key Takeaway
A stack of plain unmarked hardcover books in muted grey, cream and navy on a weathered oak desk, a plain closed notebook and a matte black fountain pen beside the stack, a glass of still water in soft morning window light, no people.

Key takeaways

What to remember

  • Nothing in the current literature supports cold water as a hormonal intervention.
  • The claim rests on a 1993 rat paper, a mixed 2007 human paper, and adjacent citations.
  • None of those measured what 'raises testosterone' means in the popular claim.
  • Cortisol responds more consistently to cold; the testosterone signal is thin.
  • If your reason to plunge is hormone optimization, pick a better reason.

The short answer

The internet has decided cold plunging raises testosterone. The published evidence for that specific claim is a single rat study from 1993, a couple of small mixed-effect human papers, and a lot of confident tweets citing the first two. Nothing in the current literature supports using cold water as a hormonal intervention, and the studies that get quoted most often measured things that are not what "raises testosterone" means in the popular claim. If the reason for starting a plunge is testosterone, the reason will not survive contact with the research.

What the studies actually looked at

Three papers keep resurfacing when the testosterone claim shows up online. It helps to look at what each one measured.

The 1993 rat study measured serum testosterone in male rats after four-hour daily immersions in 41°F water over several weeks. The rats' testosterone dropped acutely and then recovered; the paper is often cited as showing "cold water raises testosterone," which it does not, because it is a paper about rats and about drops.

A 2007 human paper on Finnish winter swimmers looked at hormonal changes after brief cold-water immersion sessions. Testosterone was one of several markers followed. The results were mixed, with some small transient changes and no consistent direction across subjects.

A 2016 study on scrotal cooling and semen quality gets cited by adjacent posts, though it is not really a testosterone paper at all. It is about sperm and temperature, and the mechanism proposed there is local to the testes, not systemic to the endocrine system.

That is the substrate the claim is built on. Three papers, one animal, none of them designed to answer the question the online version asks.

A plain clear glass jar half full of ice cubes on a light pine kitchen counter in soft morning window light, a folded linen tea towel beside it, no people.
The kitchen version of the practice is where most home plunges start. Water, ice, a jar to measure with. The endocrinology is somewhere else entirely.

What "raises testosterone" would actually mean

For the popular claim to be true, a measurable rise in total testosterone would need to appear, not just a transient shift in one downstream marker. The rise would need to persist past the session rather than settle back within the hour. And it would need to hold across weeks of practice, not appear once and vanish.

None of the current papers show this. Some observe short post-immersion changes in one direction, others show changes in the other direction, and nobody has run the kind of study that would settle the question. That would look like a proper protocol, a control arm, repeated measures, and a sample size in the hundreds rather than the tens.

Absence of evidence is not evidence of absence. The narrower claim is this: the current evidence does not support the popular version, and treating cold water as a hormone-optimization tool is inference stretched well past what the studies actually said.

The nuance: what cold water does seem to do

Research suggests cold water immersion has modest effects on things that are easier to measure than testosterone. Some studies observe reduced perceived stress and improved mood in the hours after a session. Some observe changes to sleep patterns in people who plunge earlier in the day. Some observe short rises in noradrenaline and dopamine markers, which the coldbrrr piece on cold plunges and dopamine gets into in more detail. The effect sizes are usually small and the studies are usually short.

Any of those could plausibly nudge the hormonal picture indirectly. Better sleep, less felt stress, and steadier morning behaviour are all things the endocrine system responds to. But "cold water may improve sleep, which could help hormone balance broadly" is a very different sentence to "cold plunging raises testosterone." The first is a reasonable extrapolation from thin evidence. The second is a marketing claim with a thermometer on it.

A cool grey stone bathroom windowsill in soft north-facing light, a plain closed hardcover notebook beside a matte white stoneware teacup with brown detail, a small potted plant blurred in the background, faint condensation on the window glass, no people.
The after-the-session picture. Warmth, quiet, and a notebook nobody has written testosterone numbers in.

Does cold plunging lower testosterone?

Some of the animal literature and some scrotal-temperature reasoning suggests prolonged cold exposure could produce small acute drops rather than rises. The human evidence is not strong enough to make that claim confidently either. Both the "raises T" and "lowers T" versions of the story are running past what the studies actually show.

Should men cold plunge for hormone optimization?

Not for that reason alone. The evidence base is too thin to make hormone effects a sensible primary motive. There are better reasons to plunge, including the ones the research supports at modest strength, and none of them require the testosterone story to be true.

What about cortisol and DHEA?

Cortisol is easier to measure than testosterone and shows more consistent short-term response to cold water, generally trending toward an acute rise during immersion and settlement afterward. That cardiovascular-adjacent response is part of why the coldbrrr piece on cold plunges and high blood pressure routes so much through the specialist first. DHEA gets mentioned occasionally in the swimming literature but has not been well characterised. Neither of these supports the popular hormone-optimization narrative either.

How long would you have to plunge to see hormonal effects?

Nobody knows, because nobody has run the study. Anyone offering a specific number in weeks or minutes or degrees is guessing.

For a fuller look at how cold-water research holds up against what the internet claims for it, the science pillar collects the pieces where the actual studies get measured against the online version.

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The four bits of kit that make a first plunge less of an experiment.

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