Two hundred and fifty percent. That number gets thrown around a lot in cold exposure circles, and I understand why — it sounds almost too good to be true. But it comes from real research, and Huberman explains the mechanism clearly: cold water immersion triggers a surge of norepinephrine and epinephrine, followed by a sustained rise in dopamine that can persist for hours after you climb out. Not a spike that crashes. A genuine elevation of baseline.
That distinction matters enormously. Most dopamine triggers — coffee, social media, even exercise — produce a peak and a trough. The trough is what makes you reach for more. Cold exposure, uniquely, appears to sustain dopamine without the subsequent crash. You feel better for longer, not just immediately.
Our knowledge base has a rich picture of cold water immersion research. The 2013 review on cryotherapy confirms the physiological basis — catecholamine release is well-documented, consistent, and dose-dependent. The 2023 leukocyte study adds another dimension: three weeks of repeated cold water immersion reduced mean arterial pressure and heart rate, suggesting the nervous system itself adapts over time. You're not just getting a chemical hit. You're recalibrating your baseline stress response.
The testosterone connection is where I'd urge a little more patience. The dopamine-to-luteinizing-hormone-to-testosterone pathway is biologically plausible, and it's the kind of mechanism that makes intuitive sense. But "very likely increases testosterone" is honest scientific language for "we see a mechanism, not yet a clean human trial." That's not a reason to dismiss it — it's a reason to treat it as a promising signal rather than a settled fact.
Temperature range is one area where there's genuine agreement across the research. Somewhere between 50 and 60 degrees Fahrenheit is the practical sweet spot — cold enough to trigger the catecholamine response, manageable enough to stay safe and build consistency. Lower temperatures don't necessarily produce better outcomes. They produce more shock, more risk, and often, shorter sessions. Duration and regularity beat intensity every time.
Start with your shower. Finish cold, for two minutes, every morning for two weeks. Don't chase the dramatic plunge before you've built the habit. The discomfort you feel in that first thirty seconds? That's your sympathetic nervous system doing exactly what it's supposed to. Let it settle. Breathe through it. That settling is the training.
Here's what I find most interesting when I look across everything we've indexed: the cryotherapy history paper notes that cold exposure has been used for millennia, long before anyone understood dopamine or luteinizing hormone. Cultures that had no mechanism to explain it still knew, intuitively, that regular cold exposure changed how people felt and performed. The neuroscience we have now isn't discovering something new. It's finally explaining something ancient. That continuity — from ancient practice to modern protocol — tells me this is a signal worth taking seriously.