Wim Hof breathing: what it is and how to stay safe

What the breathing involves

The Wim Hof method, named after the Dutch “Iceman” Wim Hof, has three parts: breathing, cold exposure and meditation. The breathing is done in rounds. Descriptions vary a little between studies, but a round usually looks like this:

1. About 30 deep, fast breaths, in through the nose if you can and out through the mouth without pushing.
2. Breathe out and hold with empty lungs. In the first big study, participants held for about two to three minutes, as long as they chose.
3. A recovery breath: breathe in fully and hold for about 10 to 15 seconds.
4. Repeat for about three rounds.

What happens in your body

Fast, deep breathing blows off carbon dioxide. In one study, the blood became so alkaline that its pH rose to as much as 7.75. During the hold that follows, oxygen falls: in trained participants, blood oxygen saturation typically dropped to around 50% for about 10 seconds in each round. Those participants were lying down with a doctor present.

The key point is how the urge to breathe works. Your breathing is regulated mainly to keep carbon dioxide stable (more in how breathing works). Because the fast breathing has lowered carbon dioxide, it takes longer to build up to the level that makes you gasp, and oxygen can fall low enough for you to black out before you feel the need to breathe.

Why never in water

This is the same mechanism behind blackouts and drownings in swimmers who hyperventilate before swimming underwater:

• In New York State, 16 such cases were recorded between 1988 and 2011, and 4 of the swimmers died. All four were young, strong swimmers who had deliberately hyperventilated, and almost all the incidents happened in regulated pools.
• In Australia, blackout from lack of oxygen was linked to 22 drowning deaths between 2002 and 2015, about two a year.

Drownings during Wim Hof style breathing have been reported in the media, but there are no reliable published counts. The risk does not depend on the name of the method: hyperventilating and then holding your breath in water can kill.

The method’s own safety guidance says never to do the exercises before or during diving, driving, swimming or taking a bath, to sit on a couch or the floor, and that if you faint you went too far. It also advises against practising during pregnancy or with epilepsy, and recommends seeing a doctor first if you have heart problems. Research studies have excluded people with heart disease, seizures or pregnancy for safety reasons.

The cold part

Cold water brings its own risks. Sudden immersion causes cold water shock: a gasp, rapid breathing and a sharp rise in heart rate and blood pressure, which can trigger heart problems even in fairly young, healthy people. The first effects pass within about a minute. The British Heart Foundation advises anyone with a heart condition to talk to their doctor before cold water swimming.

What research shows

• Immune response. In 2014, 24 healthy young men were randomised. The 12 trained in the method had higher adrenaline and a weaker inflammatory response and fewer flu-like symptoms after an injection of a bacterial toxin. A follow-up study with 48 men found that the breathing alone dampened the inflammatory response, and cold training made the effect stronger.
• Mood. In a 2023 study, 108 people practised for 5 minutes a day for a month. A version of this breathing improved mood, but not significantly more than mindfulness meditation. The technique with the clearest benefit was cyclic sighing, the physiological sigh: two breaths in and a long, slow breath out.
• Overall. A 2024 review found only 8 trials. Most had high concerns about bias, and 86% of participants were men. The authors concluded that the method may have promising effects on the immune system, but better research is needed.

If you try it

Sit or lie down on a soft surface, away from water, and never while driving. Keep the holds comfortable rather than pushing to the limit, and stop if you feel faint. If what you want is to calm down, a slow breath with a long exhale, such as the physiological sigh, does that without the risk.