The Wim Hof Method is famous for ice baths — but the science points to a more nuanced conclusion: in a laboratory model, the breathing does the main work in damping inflammation, and the cold mainly adds to it. In landmark research at Radboud University in the Netherlands, trained practitioners were able to voluntarily activate their sympathetic nervous system and blunt their body's inflammatory response to an injected bacterial toxin — something long considered impossible, because the autonomic nervous system was assumed to be beyond conscious control. A later Radboud study separated the method's ingredients and found that cold exposure alone did not meaningfully change inflammation, the breathing technique did, and adding cold training strengthened the breathing effect. In that one pilot study, the breath was the active part; the cold added to it but did not produce the effect on its own.
The study that broke a dogma
For decades, physiology textbooks held a firm line: you cannot consciously control your autonomic nervous system or your innate immune response. That's why it's called autonomic — it runs itself. Wim Hof, a Dutchman known for extreme cold feats, claimed otherwise. Rather than dismiss him, researchers at Radboud University Medical Centre tested him.
In a 2014 study (Kox, Pickkers and colleagues, published in PNAS), 12 people trained in the Wim Hof Method — along with a control group — were injected with endotoxin (a piece of bacterial cell wall that triggers a temporary, controlled inflammatory reaction, normally producing flu-like symptoms for a few hours). The trained group used the method's breathing during the challenge. The results were striking: they showed increased adrenaline release, activated their sympathetic nervous system on demand, and had lower levels of pro-inflammatory proteins, higher levels of an anti-inflammatory one, and milder flu-like symptoms. In this laboratory model, they had voluntarily dampened their innate immune response. This challenged the assumption that the autonomic and innate immune systems are entirely beyond conscious influence.
The follow-up that isolated the active ingredient
A single dramatic study invites a fair question: which part of the method did it — the breathing, the cold, or the mindset? A 2022 Radboud pilot study (Zwaag et al., 48 healthy young men) separated the components.
Cold exposure training alone did not meaningfully change the inflammatory response; the breathing exercise did; and adding cold training strengthened the breathing exercise's effect — the combination worked best. The findings come from a laboratory model in healthy young men, not from people with inflammatory disease.
Why this matters — and what it doesn't mean
This is genuinely important, and it's easy to overstate, so here's the honest framing. It means:
- •In one pilot study, the breathing was the active part. Breathing alone changed the inflammatory response in the lab model; cold alone did not. Cold training added to the breathing effect, so the combination worked best — but the cold was not the source of the effect.
- •Conscious influence over "automatic" systems is real, within limits. Trained people measurably shifted their immune and autonomic response. That's remarkable, but so far it has been shown only in small laboratory studies in healthy volunteers.
It does not mean you become immune to disease, or that breathing cures inflammatory illness. As the researchers themselves are careful to note, this is a temporary, controlled activation — a proof that the lever exists, not a treatment. Overselling it ("breathe away your autoimmune disease") goes far beyond what the science supports — the same overclaiming trap covered in the honest limits of breathing and cold.
How does Wim Hof breathing work?
The Wim Hof breathing is a form of controlled hyperventilation: rounds of deep, full breaths followed by a breath-hold. Physiologically, it drives a strong, deliberate sympathetic surge — including the adrenaline release seen in the studies — which is what appears to modulate the subsequent immune response. This is notably different from slow, calming breathwork: where slow breathing at six breaths per minute is associated with higher vagally mediated HRV — the calming, "rest and digest" direction — Wim Hof breathing intentionally activates the sympathetic system first. Both are legitimate tools with different purposes — one calms, the other primes and, in this research, changed a laboratory inflammatory response.
Because it's an intense technique, it should be done seated or lying down — never in or near water (including baths and cold plunges) and never while driving, because the breath-holds can cause light-headedness or fainting without warning. If you have epilepsy, heart disease or high blood pressure, are pregnant, or have panic attacks, talk to a doctor first. More in fast breathing: what the evidence shows.
See your own response
The autonomic shifts behind this research show up in your heart rhythm. ONDA reads your pulse from your phone camera, or your HRV from Apple Health (Apple Watch or another tracker that syncs there), so you can watch how intense breathing drives your heart rate up — the sympathetic activation these studies measured — versus how slow breathing settles it back down. Seeing the two opposite effects in your own numbers makes the difference between "priming" and "calming" breathwork concrete.