Why can't you hold your breath when scuba diving?
Updated 2026-06-30 · Skills & Safety
You can't hold your breath scuba diving because the air in your lungs expands as you ascend and the pressure around you drops. If you hold a full breath and rise, that expanding air has nowhere to go and can over-stretch and tear lung tissue — the most serious injury in diving. Breathing continuously lets the extra air escape naturally, so you stay safe.
This is the number one rule of scuba, and it follows directly from a simple piece of physics (Boyle's Law). Understand it once and it becomes second nature.
The physics: expanding air
Gas volume changes with pressure: squeeze a gas and it shrinks; release the pressure and it expands. As you ascend, water pressure falls, so any air trapped in your lungs expands. The biggest, fastest change happens near the surface — which is exactly where a held breath is most dangerous, even in shallow water.
What can go wrong
Holding your breath on ascent can cause lung over-expansion injury (pulmonary barotrauma). In the worst case, air forced into the bloodstream causes an arterial gas embolism — a medical emergency. These are rare precisely because the rule is drilled into every diver from day one.
How to follow the rule
Simply breathe slowly and continuously the entire time you're on scuba — never skip-breathe or pause to 'save air'. If you ever need to ascend without a regulator in your mouth (an emergency), you keep your airway open and exhale a steady stream of bubbles all the way up. Slow, relaxed breathing also calms you, improves buoyancy and makes your air last longer.
Frequently asked questions
What happens if you hold your breath while scuba diving?+
If you hold your breath and ascend, the air in your lungs expands and can over-stretch lung tissue, causing a lung over-expansion injury or, rarely, an air embolism. That's why the rule is to breathe continuously and never hold your breath on scuba.
Can you hold your breath at the bottom if you stay level?+
It's still a bad habit. Even small depth changes near the bottom change the air volume, and the rule of continuous breathing keeps you safe and relaxed. Always breathe normally.
Is it the same as free diving?+
No. Free divers hold one breath of surface air and their lungs simply return to normal size on the way up. Scuba divers breathe pressurised air at depth, so a held breath expands dangerously on ascent.