What is decompression sickness (the bends)?
Updated 2026-07-01 · Physiology
Decompression sickness (DCS), commonly called 'the bends', is an injury caused when nitrogen absorbed under pressure forms bubbles in your tissues and blood because you ascended too fast or stayed too long at depth. Those bubbles can cause anything from joint pain and fatigue to serious neurological symptoms.
The good news: DCS is largely preventable. Diving within your no-decompression limits, ascending slowly, and making a safety stop keep your nitrogen load low enough to surface safely.
Why it happens
Under pressure your body absorbs extra nitrogen from the air you breathe. On a slow, controlled ascent that nitrogen comes out gradually and leaves harmlessly through your lungs. But if you ascend too quickly or exceed your no-decompression limit, it can't escape in time and forms bubbles — like opening a shaken soda bottle.
Symptoms to know
DCS can appear during or within hours after a dive. Common signs include:
- ·Joint and muscle pain (the classic 'bends')
- ·Unusual fatigue
- ·Tingling, numbness or weakness
- ·Dizziness, confusion or difficulty breathing (more serious)
Prevention and treatment
Prevent it by staying well within your no-decompression limit, ascending slowly (no faster than about 18 m/60 ft per minute), making a 3-minute safety stop at 5 m, staying hydrated and adding conservatism for repetitive or cold dives. If DCS is suspected, the diver breathes 100% oxygen and seeks emergency care — definitive treatment is a hyperbaric (recompression) chamber. Never ignore symptoms after diving.
Frequently asked questions
What causes the bends in diving?+
Ascending too fast or staying too long at depth, which lets absorbed nitrogen form bubbles in the body instead of leaving gradually through the lungs. Diving within no-decompression limits and ascending slowly prevents it.
What are the symptoms of decompression sickness?+
They range from joint and muscle pain, unusual fatigue, and tingling or numbness, to more serious dizziness, confusion or breathing difficulty. Symptoms can appear during the dive or within hours afterward and should never be ignored.
How is decompression sickness treated?+
The diver is given 100% oxygen and taken for emergency medical care; the definitive treatment is a hyperbaric recompression chamber, which shrinks the nitrogen bubbles and restores normal blood flow. Prompt treatment greatly improves the outcome.