The Wim Hof breathing technique

Rounds of deep cyclic breathing followed by a breath retention on the exhale.

Why it works

The rapid deep breathing blows off carbon dioxide (hypocapnia), which raises blood pH and shifts autonomic balance, producing tingling, light-headedness, and a sympathetic surge often followed by calm. Lowered CO2 also lets you hold your breath longer than feels intuitive. The state shift is real chemistry, not mysticism — but the same hypocapnia is exactly what makes it dangerous near water.

How to do it

1. Sit or lie down somewhere safe — never in water, in a bath, or while driving.
2. Take 30–40 deep breaths (full inhale, relaxed exhale), then exhale and hold.
3. When you feel the urge to breathe, inhale fully and hold for ~15 seconds, then repeat for a few rounds.
4. Stop immediately if you feel faint beyond mild tingling; resume normal breathing.

Evidence

A controlled study found that practitioners trained in the method, using the breathing, could blunt the inflammatory response to an injected endotoxin — a genuine, replicable-in-principle physiological effect. That is much narrower than the broad health claims made for it. (rct)

The endotoxin study was a specific, artificial challenge in trained subjects; it does not show the method treats real illness. Crucially, the breathing causes hypocapnia and can trigger fainting — NEVER do it in or near water, and skip it if pregnant or with a cardiac or seizure condition without medical clearance.

Sources

• Kox et al. (2014), voluntary activation of the sympathetic nervous system and attenuated innate immune response, PNAS

Common mistake

Doing the breathing in a pool, bath, or before a cold plunge to "tough out" the hold. The breath-hold can cause a sudden blackout (shallow-water blackout); people have drowned this way. Land only, always.