Why You Should Never Hold Your Breath While Scuba Diving

Never hold your breath while scuba diving. It's the first rule taught in every Open Water course, usually before anyone explains why it matters. The reason isn't caution for caution's sake: holding your breath on ascent can rupture lung tissue in as little as one to two metres of depth change, and the resulting injury, arterial gas embolism, is one of the fastest-acting emergencies in diving. This is a case where the simple rule and the underlying physics agree completely.

The Mechanism: Boyle's Law

Gas expands as pressure decreases. That's Boyle's Law, and it's the entire reason this rule exists. At the surface, your lungs hold a normal volume of air at normal pressure. As you descend, increasing water pressure compresses that air, so your scuba regulator delivers air at matching pressure to keep your lungs comfortable. The reverse happens on ascent: as pressure drops, that same air wants to expand back out.

Normally, this isn't a problem. You breathe continuously, and expanding air simply exits through an open airway as you exhale. The danger appears only when the airway is closed, whether from deliberately holding a breath, panic, or even an involuntary spasm, and expanding air has nowhere to go.

What Actually Happens to the Lungs

With a closed airway, expanding gas has no exit route, so pressure builds inside the lungs faster than the tissue can accommodate. Alveoli (the lung's small air sacs) can tear under that pressure. This is called pulmonary barotrauma, sometimes described less precisely as "burst lungs," and it can occur from a change of as little as three to five feet of depth. It isn't linked to how deep the dive was, how long it lasted, or how much nitrogen was absorbed. A held breath on the way up from a shallow safety stop carries genuine risk, not just a deep technical dive.

Torn lung tissue can release air into several places, producing different injuries depending on where it ends up: air trapped around the heart and windpipe (mediastinal emphysema), air collapsing a lung (pneumothorax), or air escaping into the bloodstream itself.

Why Arterial Gas Embolism Is the Real Emergency

The most dangerous outcome is arterial gas embolism (AGE): air forced through torn lung tissue directly into the arterial bloodstream. Once in the arteries, gas bubbles can travel to the brain or heart and block blood flow there, causing symptoms that can appear within minutes of surfacing, including confusion, weakness, vision changes, or loss of consciousness. Because the onset is so fast, AGE is treated as one of diving's true medical emergencies, on the same tier of urgency as anything requiring immediate evacuation.

Arterial gas embolism following pulmonary barotrauma is a recognised contributor to diving fatalities. It is also entirely preventable, which is precisely why the "never hold your breath" rule gets repeated so often in training that it can start to sound like background noise. It isn't.

It's Not Always Deliberate

Most divers know the rule and don't intentionally hold their breath. The genuine risk usually comes from moments where breath-holding happens without a conscious decision: panic during an unexpected situation, an out-of-air scenario, coughing, or sneezing underwater. Worth noting too: holding a breath underwater often makes a diver positively buoyant, triggering an involuntary ascent at exactly the moment breath-holding is most dangerous.

How to Actually Prevent It

The prevention is procedural rather than complicated:

• Breathe continuously and normally throughout every phase of the dive, including ascent
• Ascend slowly, at the rate taught in training, since faster ascents mean faster gas expansion in the lungs
• In an emergency or out-of-air ascent, keep exhaling the entire way to the surface, even without a regulator in your mouth
• Treat any chest pain before, during, or after a dive as a possible sign of pulmonary barotrauma and seek medical evaluation, even if it seems minor

Frequently Asked Questions

How deep does a breath-hold need to be to cause injury?
Injury can occur from a depth change as small as three to five feet (roughly one to two metres). It's the pressure change, not the absolute depth, that matters.

Is this only a risk on deep or technical dives?
No. Pulmonary barotrauma isn't linked to dive depth, duration, or nitrogen absorption. It can happen on a shallow recreational dive just as easily as a deep one.

What are the warning signs of pulmonary barotrauma?
Chest pain, shortness of breath, coughing (sometimes with blood), voice changes, or a feeling of being struck in the chest. Some divers show no immediate symptoms until air has moved into surrounding tissue or the bloodstream.

What should I do if I suspect a lung overexpansion injury?
Treat any chest pain during or after a dive as a medical concern and seek evaluation immediately. If neurological symptoms appear (confusion, weakness, vision changes), treat it as a diving emergency requiring urgent medical care.

Can this happen even if I'm careful?
It's rare among divers who breathe continuously and ascend at a controlled rate. Most cases stem from panic, an out-of-air situation, or an involuntary breath-hold rather than deliberate risk-taking, which is why the "never hold your breath" habit is drilled from the very first training dive.

This article is general information about diving physiology, not a diagnosis or medical assessment. Chest pain or breathing difficulty during or after a dive should always be treated as a medical concern.