Decompression Sickness Symptoms and First Aid for the Bends

What is decompression sickness?

Decompression sickness (DCS), also called the bends, happens when nitrogen that dissolved into your tissues at depth comes out of solution as bubbles because the pressure around you dropped too quickly. The bubbles can block small blood vessels, trigger inflammation and damage tissue. Joints, skin, spinal cord, brain, inner ear and lungs can all be involved.

DCS and arterial gas embolism (AGE) together are called decompression illness (DCI). Serious cases are uncommon, and the estimates vary with the kind of diving. A 2024 review puts confirmed DCS at about 1 case per 10,000 recreational air dives in prospective studies, while StatPearls cites 3 per 10,000. DAN has recorded 1 case per 25,000 dives on Caribbean liveaboards and 1 per 600 on cold-water wreck dives.

This page is general information, not medical advice. Anyone with possible DCS needs a medical evaluation, ideally by a doctor trained in diving medicine, even if the symptoms fade on oxygen. More on staying safe in the water is in our safety guides.

Decompression sickness symptoms and when they start

DAN lists joint pain and numbness or tingling as the most common signs, followed by muscle weakness and being unable to empty a full bladder. Most cases start quietly: an ache in one joint or a patch of pins and needles that the diver blames on heavy lifting, overexertion or a tight wetsuit.

Timing narrows it down. DAN says signs usually appear between 15 minutes and 12 hours after surfacing, and in severe cases before or right after surfacing. StatPearls puts about 75% of cases within the first hour. In one series of more than 5,000 cases cited by the 2024 review, 98% of severe cases began within an hour and 99% of all cases within 6 hours.

Later onset is rare but possible, especially after a flight or a drive over high ground. The review also notes that divers sometimes misreport when symptoms began, so no cut-off makes DCS impossible. Past 6 hours, doctors look harder for other causes.

Diving doctors separate mild DCS (limb pain, rash, patchy tingling, lymphatic swelling, general symptoms) from everything else, because mild cases usually settle even without chamber treatment. The label only holds if symptoms are not getting worse, and it normally needs a neurological exam to rule out anything more serious. That is a decision for the doctor on the phone, not a reason to skip the call.

How DCS differs from arterial gas embolism

Arterial gas embolism (AGE) gets its bubbles from a different place. If air is trapped in the lungs during ascent, for example after breath-holding or a panicked ascent, the expanding gas can tear lung tissue and send bubbles straight into the arteries. The brain receives the largest share of blood flow, so it takes most of the damage. AGE can happen on very shallow dives that would never cause DCS.

In a series of 117 AGE cases, loss of consciousness and sensory changes each appeared in 39%, confusion in 37% and one-sided weakness in 27%. Lung signs such as chest pain or coughing up blood were present in only 58%, so their absence does not rule AGE out. Half of these divers improved on their own and a few relapsed afterwards. The 2024 review advises evacuation for AGE even after an apparent recovery.

On the dive boat you do not need to tell the two apart. DAN states that early management of AGE and DCS is the same, and the 2024 review notes that AGE is never considered mild.

First aid for the bends, in order

Act on suspicion. DAN's instruction is to give emergency oxygen right away, contact local emergency medical services first and then DAN. The 2024 review lists the same core steps for an early case: life support, positioning, oxygen, fluids, then reporting to a diving medicine expert.

Oxygen often makes symptoms fade, sometimes completely. DAN warns that they can return once the oxygen stops, so improvement is not a reason to cancel the medical evaluation.

• Get the diver out of the water and check breathing. If there is no breathing and no pulse, start CPR and arrange evacuation at once, adding oxygen to the rescue breaths if you can.
• Start oxygen at the highest concentration you can deliver, aiming for 100%. For a conscious diver who is breathing, a demand valve with a mouthpiece and nose clip works best. A non-rebreather mask with a reservoir bag at 15 L/min is the fallback. Simple face masks without a reservoir do not give 100%, even at high flow. Skip air breaks early on unless a diving medicine expert asks for them, and make sure the oxygen will last the whole evacuation.
• Call local emergency services, then the DAN emergency line below. Say it is a diving emergency.
• Lay the diver flat on their back. Use the recovery position if they are drowsy, unconscious or vomiting. Do not tilt the head down; that advice was dropped. If AGE is possible, do not make the diver stand up to test balance, because moving upright has occasionally been followed by a fresh embolism.
• If the diver is fully conscious, give fluids by mouth: water or an isotonic drink, nothing fizzy, caffeinated or alcoholic. Give nothing by mouth to a drowsy or deteriorating diver.
• Keep the diver comfortably warm but not hot. Skip the hot shower, since rapid warming after a dive can promote bubble formation.
• Hold off on painkillers until medical staff advise them. That is DAN's guidance, and StatPearls notes that aspirin can mask pain and other symptoms. The 2024 review considers an oral anti-inflammatory the one drug with evidence for field use, so leave that call to the doctor on the phone.
• Write down every dive from the last 48 hours (depth, time, ascent rate, surface intervals, gas), when each symptom started and how it changed, and when oxygen began. A good dive log makes this quick. DAN's on-site neurological check needs no medical training, but it must not delay evacuation.

DAN emergency numbers

Call your local emergency number first. Then call DAN: its medical staff answer 24 hours a day, can consult with the local doctor and can refer the diver to a suitable chamber. The numbers below are copied from DAN's own pages. Save the one for your region in your phone before the trip.

Expect questions about your location, a call-back number, the diver's age and medical history, the dives, when symptoms started and what first aid was given. DAN says arranging care can take 30 minutes or longer, so if the situation is life-threatening, get the diver to the nearest medical facility first and call from there. Do not turn up unannounced at the nearest chamber. Some do not treat divers at all hours, and not every diving injury is DCS.

What not to do

DAN and the diving medicine literature single out three things to avoid.

• Do not put the diver back in the water. DAN says there are probably more situations where in-water recompression should not be tried than where it is reasonable, and the general rule is first aid on the surface. The medical consensus accepts it only when the chamber is more than two hours away and everyone involved is trained to decompression-procedures level, breathing oxygen no deeper than 9 m (30 ft) with a full-face mask or mouthpiece retainer, among other conditions. In-water recompression on air is not recommended, and the UHMS says that with severe symptoms or signs of AGE the risk of harm probably outweighs any benefit.
• Do not fly, and avoid driving over high ground. Lower pressure lets bubbles grow, and DAN says a diver with symptoms must seek treatment before flying. If evacuation by air is needed, it should be in a pressurized aircraft or a helicopter kept below about 300 m (1,000 ft).
• Do not wait to see. DAN calls denial arguably the worst symptom of DCS. In serious DCS, incomplete recovery after treatment rose from about 40% when recompression started within 6 hours to 60% after longer delays, and DAN notes that treatment may work less well after 24 hours. Late treatment can still help, so a delay is not a reason to skip the call.

Risk factors for decompression sickness

Your dive profile matters most: depth, time and ascent rate. DAN lists the established risk factors for divers as deep or long dives, cold water, heavy exercise at depth and rapid ascents. Flying or other altitude exposure too soon after diving adds to them.

Nitrox dived on air limits cuts nitrogen uptake, which DAN describes as a way to build a safety buffer. Our nitrox calculator shows the depth limits that come with each mix.

• Temperature pattern: in human experiments, being warm at depth and cooling during the ascent carried at least ten times the risk of the reverse pattern.
• Exercise: hard work at depth increases nitrogen uptake, and lifting or straining after the dive may push bubbles through a shunt in the heart. A hot shower or hot tub straight after diving can bring on skin symptoms.
• Patent foramen ovale (PFO): a small opening between the upper chambers of the heart, found in about 25% of adults. The larger ones, present in under 2% of people, are the ones most linked to DCS, and screening every diver is not recommended.
• Weaker evidence: obesity, dehydration, heavy exercise right after surfacing and lung disease. The 2024 review calls dehydration widely accepted as a risk factor but not strongly proven.

Why "undeserved" bends happen

Plenty of divers get DCS without breaking a rule. DAN states that bubbles can form even when accepted guidelines are followed and that almost any dive profile can result in DCI. In one series of 52 mostly mild cases from table-planned dives, 20 divers had stayed within their table.

The reason is how limits are built. A table or computer limit is not a line between safe and bent. The 2024 review describes it as a point on a continuum of risk that the designer judged acceptable, and that applies to printed tables such as DECO 2000 as much as to computer algorithms. People also vary: a US Navy analysis found that the same diver produced very different bubble levels after identical dives, and DCS occurred almost only on the high-bubble days. A large PFO, cooling on the ascent and hard work at depth all shift the odds without changing the limit your computer shows.

So "I was inside my limits" is not evidence against DCS. Doctors judge the symptoms and their timing first, and the profile adds context.