The Wim Hof Method is a breathwork and cold-exposure practice developed by the Dutch athlete Wim Hof, built on three pillars: a cycle of deep, rapid breaths followed by a breath hold, gradual exposure to cold, and commitment, now usually called mindset. It is the best-known modern form of breathwork, the umbrella term for deliberately changing the pace, depth and pattern of breathing to influence how the body and mind feel.
It matters because breathing is the one part of the autonomic nervous system most people can steer at will, and controlled studies, starting with a 2014 paper in PNAS, show that breathing techniques measurably shift stress hormones and mood. The same research shows where the evidence stops, and the safety record shows that some techniques are dangerous in the wrong setting.
Safety first. Never practise breath holds or fast, deep "power breathing" in or near water, in the bath or shower, while driving, or while standing. Hyperventilating before a breath hold can cause a blackout without warning. Sit or lie down somewhere safe. If you are pregnant, or have epilepsy, heart disease, high blood pressure, Raynaud's phenomenon or a history of fainting, speak to a clinician before trying intense breathwork or cold exposure.
What is breathwork?
Breathwork is any deliberate pattern of breathing used to change physical or mental state. The main families are slow breathing (roughly five or six breaths a minute), extended-exhale breathing, breath holds, and fast cyclic breathing in which a series of deep, quick breaths is followed by a pause.
None of this is new. Classical yoga calls breath regulation pranayama. Patanjali's Yoga Sutras list it as the fourth of the eight limbs of yoga, and the Hatha Yoga Pradipika, a fifteenth-century manual attributed to Svatmarama, devotes a chapter to breath retention and techniques such as kapalabhati, a rapid, forceful exhalation exercise. Modern methods, Wim Hof's included, are recognisable descendants; the guide to kundalini, the yoga texts and safety covers the energetic side of that tradition. What has changed is measurement: researchers can now track respiratory rate, blood gases and hormones while people breathe.
What are the three pillars of the Wim Hof Method?
The Wim Hof Method rests on three pillars: breathing, cold exposure and commitment (presented on the official site today as mindset, meaning attention, willpower and intention).
The breathing pillar is the distinctive part. A round typically consists of around 30 deep, rapid breaths, which amounts to controlled hyperventilation, followed by a breath hold after exhaling and a short recovery breath. Researchers call it "cyclic hyperventilation followed by breath retention." Hyperventilation blows off carbon dioxide and makes the blood more alkaline; the hold then briefly lowers blood oxygen.
The cold pillar involves gradual exposure to cold showers or cold-water immersion, and the mindset pillar covers meditation and focus. Hof's own instructions warn that the breathing should never be practised in water, in the shower or while driving.
What did the 2014 PNAS study actually find?
The landmark study is Kox and colleagues, "Voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans," published in PNAS (volume 111, issue 20) on 20 May 2014 by a team at Radboud University Medical Center in Nijmegen. It found that people trained in the method could voluntarily raise their adrenaline levels and showed a dampened inflammatory response to a standard laboratory challenge.
Twenty-four healthy volunteers were randomised into two groups of 12. The intervention group trained for 10 days in meditation, the breathing technique and cold exposure, including immersion in ice-cold water; the control group received no training. Everyone was then injected with a small dose of purified bacterial endotoxin, a standard research model that briefly produces flu-like symptoms.
In the trained group, the breathing caused intermittent respiratory alkalosis and low blood oxygen, and plasma epinephrine (adrenaline) rose sharply. The anti-inflammatory signalling molecule IL-10 rose faster and higher, the pro-inflammatory cytokines TNF-α, IL-6 and IL-8 were lower, and the trained volunteers reported fewer flu-like symptoms. The significance was conceptual: the autonomic nervous system and innate immune response had long been regarded as beyond voluntary control. The limits matter as much: it was a small, single-centre study of a short laboratory response, not of long-term health outcomes.
Which part of the method does the work?
A 2022 follow-up from the same Nijmegen group points to the breathing exercise as the main driver. Zwaag, Naaktgeboren, van Herwaarden, Pickkers and Kox, writing in Psychosomatic Medicine, ran two linked studies.
In the first, 40 healthy men learned two versions of the breathing, one with prolonged breath retention and one without. Both raised plasma epinephrine, regardless of training length or whether Hof or an independent instructor taught them, which suggests the long breath hold is not essential to the adrenaline response.
In the second, 48 men were randomised to cold training, the breathing exercise, both, or neither, then received the same endotoxin challenge. Cold training alone did not meaningfully change the inflammatory response. The breathing exercise did, and adding cold training strengthened it; the combination was the most potent.
A separate proof-of-concept trial led by Buijze (PLOS ONE, 2019) tested an eight-week add-on programme of breathing, cold and meditation in 24 people with axial spondyloarthritis, a rheumatic condition. It reported no safety signals and a fall in one inflammation marker (ESR) but not in hs-CRP, and the authors called for full-scale trials.
What do systematic reviews say about the Wim Hof Method?
The most cautious summary comes from Omar Almahayni and Lucy Hammond of the University of Warwick, whose systematic review of eight trials was published in PLOS ONE on 13 March 2024. They found the clearest signal was a possible anti-inflammatory response linked to raised epinephrine, while effects on exercise performance were inconsistent.
Their main caveat was quality: the trials were small, several were at high risk of bias, and more robust, confirmatory research is needed before the method can be recommended. The laboratory findings are reasonably consistent, but the claims circulating online run well ahead of the data.
How do box breathing and the physiological sigh compare?
Slower, exhale-focused techniques have their own evidence, and in the one head-to-head trial they did at least as well as fast breathing. Box breathing uses equal counts for the inhale, hold, exhale and hold. The physiological or cyclic sigh is a double inhale through the nose, the second topping up the lungs, followed by a long, slow exhale.
The key study is Balban, Spiegel, Huberman and colleagues at Stanford, "Brief structured respiration practices enhance mood and reduce physiological arousal," published in Cell Reports Medicine in January 2023. Over 28 days, 108 adults did five minutes a day of cyclic sighing, box breathing, cyclic hyperventilation with retention (a Wim Hof-style pattern) or mindfulness meditation as a comparison.
All four groups reported less anxiety and negative mood. The breathwork groups improved positive mood more than meditation, and cyclic sighing produced the biggest mood improvement and the largest drop in resting respiratory rate. It was a remote study with a mostly student sample, so it supports slow, exhale-focused breathing as a daily stress-management habit rather than proving wider health effects.
The gentler techniques also carry far less risk than hyperventilation and breath holds, and sit naturally alongside other low-risk practices such as binaural beats and grounding, or earthing.
What does the evidence say about cold exposure?
The cold-exposure evidence is mixed: some modest, short-lived effects, and plenty of claims that are not yet supported.
The largest trial is Buijze and colleagues (PLOS ONE, 2016): just over 3,000 Dutch adults finished their usual hot shower with 30, 60 or 90 seconds of cold water for 30 consecutive days, or were controls. The cold-shower groups had 29 percent less self-reported sickness absence, but no significant difference in days of illness.
Cain and colleagues' meta-analysis of cold-water immersion (PLOS ONE, January 2025) pooled 11 studies with 3,177 participants. They found a temporary rise in inflammation immediately and an hour after immersion, and lower stress 12 hours afterwards but not at other time points. Sleep quality and quality of life showed some improvement; mood did not, and the immune evidence was thin.
Cold water also carries a specific hazard. The RNLI defines cold water as anything below 15 °C, and sudden immersion triggers cold-water shock: an involuntary gasp, uncontrolled rapid breathing and a surge in heart rate and blood pressure. Physiologists including Professor Mike Tipton of the University of Portsmouth's Extreme Environments Laboratory have documented cold-water shock as a precursor to drowning and cardiac events.
Why breath holds and water never mix
The single most important safety fact about this style of breathwork is that hyperventilating before a breath hold can make a person black out without any warning. The urge to breathe is driven mainly by rising carbon dioxide, not falling oxygen. Fast, deep breathing lowers carbon dioxide first, so during the hold oxygen can drop low enough to cause unconsciousness before the body signals that it needs air. In water, that loss of consciousness, known as hypoxic or "shallow water" blackout, leads to drowning.
The US Centers for Disease Control and Prevention documented the pattern in its Morbidity and Mortality Weekly Report in May 2015. A review of New York State drownings from 1988 to 2011 identified 16 cases linked to "dangerous underwater breath-holding behaviors," four of them fatal. All four people who died were young, advanced or expert swimmers who had hyperventilated on purpose.
The rules, without exceptions. Never do breath holds or fast breathing in a pool, open water, bath or shower. Never do them while driving, cycling or operating anything. Do them sitting or lying down, on a stable surface. Stop if you feel faint, have chest pain or feel your heart racing irregularly. If you are pregnant, or have epilepsy, heart disease, high blood pressure, Raynaud's phenomenon or a history of fainting, consult a clinician before any intense breathwork or cold exposure, and enter cold water gradually, never alone.
Billy Carson's reading
There is no long-form Billy Carson lecture devoted specifically to breathwork or the Wim Hof Method, and this article does not attribute specific breathwork claims to him. What his work does show is where breath fits. In the site's pillar on biohacking for beginners, Carson's approach is framed as consciousness-first: sleep, movement, food timing and breath are treated as maintenance for the body, and the point of looking after them is to have more energy and clarity for meditation and inner work rather than to chase metrics.
Seen that way, breathwork is less a performance hack than a bridge between the body and the meditative practice that runs through his teaching on consciousness. The studies above support short, regular, low-risk practices and set clear limits on the riskier ones, the same evidence-first balance applied across the biohacking pillar, from intermittent fasting and autophagy to sleep and light exposure.
Watch, read and go deeper
For a guided starting point, the Meditation show on 4BK TV collects guided meditations and frequency sessions for relaxation, focus and sleep, which pair naturally with a few minutes of slow breathing beforehand. The biohacking for beginners guide sets breathwork alongside sleep, light, movement and fasting with the evidence for each. For every article on the subject, start at the biohacking topic hub.
Frequently asked questions
Is the Wim Hof Method backed by science?
Partly. Small controlled studies, led by the 2014 Kox paper in PNAS, show the breathing raises adrenaline and dampens the short-term inflammatory response to a laboratory endotoxin challenge in healthy volunteers. A 2024 review of eight trials found the evidence limited by small samples and high risk of bias.
Is the Wim Hof breathing technique safe?
It is never safe in or near water, in the bath or shower, or while driving, because hyperventilating before a breath hold can cause sudden loss of consciousness without warning. Healthy adults should sit or lie down on dry land. People who are pregnant or have epilepsy, heart disease, high blood pressure or a history of fainting should consult a clinician first.
What is the physiological sigh?
The physiological or cyclic sigh is a double inhale through the nose followed by a long, slow exhale. In a 2023 Stanford randomised trial, five minutes a day for a month improved mood more than mindfulness meditation and lowered resting respiratory rate.
What is box breathing?
Box breathing uses four equal counts: inhale, hold, exhale, hold. It was one of the breathwork arms in the 2023 Stanford trial. With short holds and no hyperventilation, it carries far less risk than the Wim Hof pattern.
Do cold showers help you stay well?
The evidence is modest. A 2016 Dutch trial of about 3,000 adults found that ending a shower with 30 to 90 seconds of cold water cut self-reported sickness absence by 29 percent but not days of illness. A 2025 meta-analysis found short-term effects and thin evidence on immunity.
Sources and further reading
- Kox M. et al., "Voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans," Proceedings of the National Academy of Sciences 111(20), 2014.
- Zwaag J. et al., "The Effects of Cold Exposure Training and a Breathing Exercise on the Inflammatory Response in Humans: A Pilot Study," Psychosomatic Medicine 84, 2022.
- Almahayni O. and Hammond L., systematic review of the Wim Hof Method, PLOS ONE, 2024.
- Balban M.Y. et al., "Brief structured respiration practices enhance mood and reduce physiological arousal," Cell Reports Medicine 4, 2023.
- Buijze G.A. et al., "The Effect of Cold Showering on Health and Work: A Randomized Controlled Trial," PLOS ONE, 2016.
- Cain T. et al., "Effects of cold-water immersion on health and wellbeing: A systematic review and meta-analysis," PLOS ONE, 2025.
- Boyd C. et al., "Fatal and Nonfatal Drowning Outcomes Related to Dangerous Underwater Breath-Holding Behaviors, New York State, 1988–2011," CDC Morbidity and Mortality Weekly Report, May 2015.
- Tipton M.J. et al., "Cold water immersion: kill or cure?" Experimental Physiology, 2017.
These statements have not been evaluated by the Food and Drug Administration. This content is for information only and is not medical advice. Talk to a qualified clinician before starting breathwork or cold exposure, especially if you have a medical condition or are pregnant.
