Decompression Sickness, Explained
Decompression sickness — 'the bends' — is the risk every diver plans around. Understand the cause and both the prevention and the exam questions become straightforward. (This is general education, not medical advice — always follow your training and seek professional care.)
What it is
Under pressure, extra nitrogen dissolves into your body's tissues (Henry's Law). Normally you release it gradually as you ascend and rest on the surface. But if you ascend too quickly or carry too much nitrogen, it can come out of solution as bubbles inside your body — like a shaken fizzy drink foaming when opened. Those bubbles are decompression sickness.
What raises the risk
Several things make bubbles more likely, and most are within your control:
- Ascending too fast or skipping your safety stop.
- Exceeding no-decompression limits, or diving right up to them repeatedly.
- Multiple dives a day or several days in a row without enough recovery.
- Dehydration, being cold, hard exertion, and flying too soon after diving.
Warning signs
Symptoms can appear during a dive or come on hours afterwards, and they range from mild to serious: joint or limb pain, unusual tiredness, a skin rash or itch, dizziness, numbness or tingling, and weakness. If decompression sickness is suspected, treat it as an emergency — don't wait to see if it passes.
How divers prevent it
Prevention is mostly good habits:
- Ascend slowly and always make a safety stop.
- Stay well within your no-decompression limits — dive conservatively, not to the edge.
- Hydrate, stay warm, and avoid heavy exertion around your dives.
- Wait the recommended time before flying, and use a dive computer to track your nitrogen.
First response
If a diver shows signs of decompression sickness, general first aid is to get them out of the water, have them lie comfortably, give emergency oxygen if trained and available, keep them hydrated, and contact emergency medical services or a diver emergency hotline immediately. This is an overview only — follow the emergency procedures from your training.
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Frequently asked questions
What causes decompression sickness?
Nitrogen dissolves into your tissues under pressure (Henry's Law). If you ascend too quickly, it comes out of solution as bubbles inside the body, which cause decompression sickness. Slow ascents and safety stops let the nitrogen leave gradually and safely.
What are the symptoms of the bends?
Common signs include joint or limb pain, unusual fatigue, skin rash or itching, dizziness, numbness or tingling, and weakness. They can appear during a dive or hours later. Suspected decompression sickness should be treated as an emergency.
How do divers prevent decompression sickness?
Ascend slowly, always do a safety stop, stay well within no-decompression limits, dive conservatively on repetitive and multi-day trips, stay hydrated and warm, and wait the recommended time before flying.
Why do you have to wait before flying after diving?
Cabin pressure at altitude is lower than at sea level, so flying too soon lets residual nitrogen expand and bubble more easily — raising decompression sickness risk. Waiting gives your body time to off-gas first.
Is decompression sickness an emergency?
Yes. If it's suspected, treat it seriously and seek professional medical help immediately — give emergency oxygen if trained and available and contact a diver emergency service. Do not wait to see whether symptoms pass.