Huberman's central argument here is deceptively simple: cold exposure, done consistently, can move the needle on immune function. Three sessions per week. Six weeks. Measurable trends in T lymphocytes and other immune markers. That's the promise.
And yes, the mechanism makes biological sense. When you hit cold water, your sympathetic nervous system floods your body with norepinephrine and epinephrine. In the short term, this is pro-immune. It activates immune cells, primes your defenses. Your body reads the cold as a controlled threat and responds accordingly.
Here's where it gets interesting. We have a 2023 study in our knowledge base comparing partial body cryotherapy against cold water immersion — and the cryotherapy group showed a greater increase in CD8+ T-cells compared to both the immersion group and the control. CD8+ cells are your cytotoxic killers. They're the immune system's search-and-destroy unit. More of them means a faster, more targeted response to viral threats.
What that study reveals is something Huberman touches on but doesn't fully unpack: not all cold is equal. The modality matters. The temperature matters. Full immersion, partial immersion, cold air — these produce different physiological signals. The immune response isn't just "cold = good." It's a spectrum of adaptations depending on how the stress is delivered.
The 2014 PNAS endotoxin study is also worth revisiting here. Participants who practiced cyclic hyperventilation before E. coli injections showed dramatically fewer symptoms — not because their immune system fought harder, but because the adrenaline surge modulated the inflammatory response. Less inflammation, less suffering. This is the same neurochemical cascade cold exposure triggers. Different entry point, same lever.
The consensus is clear on one point: chronic cold exposure builds resilience. The disagreement is around dosing. Huberman's three-times-per-week recommendation is conservative and probably right for most people. But the cryotherapy research suggests that for targeted immune effects, the delivery method and intensity matter more than frequency alone.
There's also universal agreement on one caution: if you're already sick, stay out of the cold. This isn't weakness — it's thermodynamics. A body fighting infection is already under metabolic stress. Cold exposure adds more. You're not helping your immune system. You're competing with it.
Three sessions per week, one to three minutes each, consistent temperature. Not heroic. Not punishing. Cold enough to feel uncomfortable, warm enough to recover quickly afterward. Nasal breathing throughout — Huberman is right that this protects your mucosal barrier, your first line of defense against airborne pathogens.
And here's the surprising connection I keep coming back to: the same inflammatory balance that governs immune function also governs muscle recovery. Our skeletal muscle research shows that cold exposure after training modulates the pro-inflammatory and anti-inflammatory ratio during repair. You're not just building immune resilience. You're shaping how every stressed tissue in your body heals. Same mechanism. Broader application than most people realize.
Cold isn't a cure. It's a calibration tool. Use it when you're strong. Rest when you're not. That distinction — simple as it sounds — is the entire protocol.