Is Wim Hof Breathing Safe? Side Effects and Contraindications

Wim Hof breathing is, for most healthy adults, a well-tolerated practice with a good safety record — provided two rules are followed without exception. It also has a genuinely dangerous edge, which is under-discussed precisely because the practice is otherwise so benign. People have died doing this. Not many, and not mysteriously: they died in water, from a mechanism that is entirely understood and entirely preventable.

This page is the honest version. Not a warning designed to scare you off a practice worth doing, and not the reassurance that comes from leaving things out.

The two rules

Never practise in or near water. Not in a swimming pool, the sea, a lake, a bathtub, an ice barrel, or a shower where you could fall. Not before swimming, and never while floating or submerged.

Always practise sitting or lying down, and stay there until the session has fully ended and normal breathing has returned.

Every serious incident associated with this method traces back to one of these being broken. Everything else on this page is detail.

Why water is the line

The breathing works by lowering carbon dioxide. That is the whole mechanism — the tingling, the warmth, the unusually long breath holds all follow from it.

The problem is that carbon dioxide is also your body's alarm. The urge to breathe comes almost entirely from rising CO₂, not from falling oxygen. Drive CO₂ low enough and you can run your oxygen down to unconsciousness while feeling calm and comfortable the entire way. There is no gasping, no panic, no signal. This is called shallow-water blackout, it is well documented in swimmers and freedivers, and it is why competitive pools ban breath-hold training (NPR, 2015).

On your bedroom floor, a blackout means you wake up a few seconds later, confused and fine. In thirty centimetres of water it means you drown, silently, while looking relaxed to anyone watching.

These are not hypothetical deaths. Fatalities have been reported in people who combined this style of breathing with water — swimmers, pool users, people practising breath holds in the bath. The instruction not to do it exists in the method's own materials and on every page of this site; it is simply very easy to underestimate, because nothing about the sensation warns you.

If cold exposure is part of your practice, the sequence is fixed: breathing on dry land, full recovery, and only then the water — breathing normally throughout the plunge.

Why you lie down

Fainting during a session is uncommon but not rare, and it is not a sign that something went badly wrong — it is the predictable end of the same physiology, arriving a little early. Lying down converts a potential emergency into a non-event.

This is also why the practice never belongs in the standing position, on a balcony, near stairs, on hard tile, at the gym between sets, or anywhere a brief loss of consciousness would mean a head injury. And it is why you never practise while driving, cycling, or operating anything.

Who should not practise this

Do not practise Wim Hof breathing, and speak with your doctor first, if any of the following apply.

Pregnancy. Deliberate breath retention reduces oxygen availability, and the effects on a pregnancy have not been studied. There is no reason to take the risk when slow breathing without holds offers the calm benefits safely.

Epilepsy or any seizure history. Hyperventilation is used clinically to provoke seizure activity during EEG testing. That is a direct contraindication, not a theoretical one.

Heart conditions, arrhythmias, or uncontrolled high blood pressure. The practice raises adrenaline deliberately and produces meaningful swings in blood pressure and heart rate.

A history of fainting or vasovagal syncope. You are already predisposed to the one failure mode this practice can produce.

Serious respiratory conditions, including poorly controlled asthma or COPD.

A history of panic attacks. This one is a caution rather than an absolute bar. The sensations of a session — tingling, light-headedness, chest tightness, unreality — are physiologically almost identical to a panic attack, because both involve low carbon dioxide. For some people that resemblance is enough to trigger the real thing. If that is you, start with slow breathing instead; nothing important is lost.

Children. This is an adult practice. Adolescents should not do it unsupervised.

Normal, and not normal

Expect tingling in the hands, face and lips; light-headedness; warmth spreading through the body; occasional mild involuntary tightening of the hands; and sometimes an emotional wave that arrives without an obvious reason. All of this is ordinary, all of it resolves within minutes of breathing normally, and none of it means you should stop practising.

Stop the session, breathe normally, and stay lying down if you experience chest pain or pressure, a pounding or irregular heartbeat that does not settle, sharp headache, genuine panic rather than discomfort, or cramping that will not release. If chest pain or an irregular heartbeat persists after you have recovered, treat it as you would any other chest symptom and seek medical attention.

Recurrent headaches after sessions usually mean you are pushing the pace or the holds. Ease off and they typically disappear.

The quiet risk: the timer

The most common way people get into trouble on dry land is not dramatic. It is treating the retention time in a guided video as a target — holding past the point where the body has clearly asked for air, because the number on screen has not arrived yet.

Every session on this site displays times as a description of the practice, never an instruction. Breathe in when you need to breathe in. A session where you breathed in at fifty seconds instead of ninety is a complete, successful session. There is no version of this practice where forcing produces a better outcome, and the one genuinely lethal mechanism sits directly at the end of that road.

What the evidence actually says about safety

Honesty requires saying that the safety data are thin. The research on this method has mostly asked what it does — immune response, autonomic control, brain activity — in small groups of screened, healthy volunteers (Kox et al., PNAS, 2014). There has been no large trial designed to catalogue adverse events, and there is no good data on rare complications or on long-term practice.

What exists is a large amount of accumulated experience — millions of people practising for years with few reported problems — alongside a small number of severe, well-characterised incidents that share a single cause. That is a reasonable basis for practising, and a poor basis for improvising.

The short version

Lie down. Stay away from water. Do not chase the timer. If you are pregnant, epileptic, cardiac, or prone to fainting, this practice is not for you — and slow breathing, which carries none of these risks, is available on every page of this site.

This page is general information, not medical advice. If you have any health condition, or any doubt about whether this practice suits you, speak with your doctor before starting.

Sources
Kox M. et al., "Voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans", PNAS 111(20), 2014 — https://www.pnas.org/doi/10.1073/pnas.1322174111
NPR Health Shots, "Breath-holding in the pool can spark sudden blackouts and death", 2015 — https://www.npr.org/sections/health-shots/2015/05/29/410331432/breath-holding-in-the-pool-can-spark-sudden-blackouts-and-death