Decompression sickness occurs when dissolved gas, usually nitrogen, forms bubbles in the body’s tissues and blood during or after a reduction in surrounding pressure. The classic scenario is a scuba diver ascending too quickly, but the same physics applies to caisson workers, aviators climbing to high altitude, and even astronauts transitioning to a low-pressure spacesuit. Once bubbles form, they can obstruct blood flow, trigger inflammation, and damage tissues ranging from joints and skin to the spinal cord and brain. The condition is treatable, but getting the details of prevention and response right matters enormously.
How Bubbles Form and Why They Cause Harm
When you breathe compressed air at depth, the increased ambient pressure forces more nitrogen (or whatever inert gas is in the breathing mix) into your tissues. The deeper and longer the dive, the more gas dissolves. During ascent, the ambient pressure drops, and if it drops faster than the gas can be carried back to the lungs and exhaled, the dissolved gas can come out of solution and form small bubbles in the tissues or in the blood vessels that drain them. These bubbles then pass into the venous circulation.1PubMed Central. Decompression illness: a comprehensive overview
The damage is not just mechanical clogging. Bubbles obstruct capillary blood flow and starve downstream tissue of oxygen, but they also set off a cascade of biological trouble: platelets clump around the bubble, clots form, and the complement system activates, amplifying inflammation.2PubMed. Microbubbles: pathophysiology and clinical implications The bubbles also injure the endothelium, the delicate lining of blood vessels, producing widespread inflammation and a shift toward abnormal clotting.3PubMed Central. Time Course of Endothelial Dysfunction Induced by Decompression Bubbles in Rats The result is that even a small number of bubbles can cause symptoms out of proportion to their size, because the body’s inflammatory response does much of the actual damage.
What It Feels Like
Decompression sickness can show up in an enormous variety of ways. It can affect the joints and muscles, the skin, the spinal cord, the brain, the inner ear, and the cardiopulmonary system, and symptoms range from mild to life-threatening.4PubMed Central. Decompression illness: a comprehensive overview Historically, diving medicine grouped cases into “Type I” (pain-only, often joint pain nicknamed “the bends”) and “Type II” (neurological or cardiopulmonary involvement), though many clinicians now prefer describing the specific organs affected rather than relying on that binary.
Joint pain, especially in the shoulders and elbows, is the symptom most people associate with the condition. But spinal cord hits are more dangerous and more common than many recreational divers realize. Numbness, tingling, or weakness in the legs can signal spinal involvement and demand urgent treatment. Skin manifestations include mottled, marbled discoloration called cutis marmorata, which can look alarming but often signals a broader systemic hit.
Inner ear decompression sickness deserves special attention because it is easy to misdiagnose. The hallmark symptoms are vertigo, ringing in the ears, and hearing loss, and they can appear alone or together. Inner ear cases have traditionally been linked to deep, mixed-gas diving, but case series have shown they can follow ordinary recreational dives as well.5PubMed. Inner ear decompression sickness after a routine dive and recompression chamber drill A review of 115 inner ear cases found that purely vestibular symptoms (vertigo and balance problems without hearing loss) were the most common presentation, appearing in roughly three-quarters of patients.6PubMed. Inner ear decompression sickness in scuba divers: a review of 115 cases A diver who feels dizzy after surfacing should not write it off as seasickness.
Who Is More Vulnerable
The frustrating truth is that two divers can do the identical dive and one gets hit while the other feels fine. Factors like age, body composition, fitness level, and the presence of a patent foramen ovale (PFO) have all been studied, but none of them, individually or combined, fully explain why bubble loads vary so much from person to person or even from dive to dive in the same person.7PubMed Central. Decompression sickness, fatness and active hydrophobic spots
PFO gets the most attention. This small opening between the right and left sides of the heart is a remnant of fetal circulation and is present in roughly a quarter of adults. Normally, venous bubbles travel to the lungs, where they are filtered out harmlessly. But if a PFO is present and allows blood to shunt from the right side of the heart to the left, bubbles can bypass the lung filter entirely and enter the arterial circulation, potentially reaching the brain or spinal cord. Evidence suggests that a PFO, particularly a large one, is associated with increased risk of neurological decompression sickness.8Journal of Education, Health and Sport. Patent Foramen Ovale as a Risk Factor for Neurological Decompression Sickness in Recreational Divers: A Narrative Review That same inner ear case review found a high prevalence of PFO in affected divers, supporting the idea that paradoxical arterial gas embolism through the heart defect is a key mechanism for inner ear hits.9PubMed. Inner ear decompression sickness in scuba divers: a review of 115 cases
Whether to screen recreational divers for PFO is debated. Some diving medicine physicians recommend screening after an unexplained neurological DCS event, particularly if the dive profile seemed conservative. A few divers who experience repeated hits opt for PFO closure, a catheter-based procedure, but this is a personal medical decision with its own risks and should be discussed with a specialist familiar with diving medicine.
Beyond PFO, higher body fat increases nitrogen loading because nitrogen is about five times more soluble in fat than in water. Dehydration, fatigue, heavy exertion at depth, and cold exposure are commonly cited as aggravating factors, though controlled data isolating each one are thin. The practical upshot is that staying well-hydrated, rested, and warm gives you a better margin, even if no single lifestyle factor is a reliable predictor.
Prevention During Diving
The primary defense against decompression sickness is controlling the ascent. Rise slowly enough and the excess dissolved gas can travel back to the lungs and leave the body without forming problematic bubbles. A study comparing two ascent rates found that climbing at about 9 meters per minute produced significantly fewer venous bubbles than ascending at 17 meters per minute.10PubMed. Ascent rate and circulating venous bubbles in recreational diving Most training agencies now recommend ascent rates no faster than 9 to 10 meters per minute for recreational diving.
Safety stops are another standard practice. Pausing at about 5 meters for three to five minutes at the end of a dive gives tissues extra time to off-gas before the final ascent to the surface. The question of whether additional “deep stops” (pausing briefly at a deeper point during ascent) add benefit has been more contentious. One controlled study found that a deep-stop protocol actually produced more precordial bubbles than a conventional shallow-stop profile.11PubMed. Bubble formation after a 20-m dive: deep-stop vs. shallow-stop decompression profiles The current consensus leans toward shallow stops being more protective for typical recreational dive profiles, though practices in technical diving can differ.
Dive computers have become the standard tool for tracking decompression obligations in real time. Most use algorithms descended from a model proposed by the physiologist John Scott Haldane over a century ago, which tracks dissolved gas in a set of theoretical tissue compartments. These models work well for single dives but can be overly liberal for repetitive dives within a 24-hour span, which has pushed developers to incorporate bubble-phase models that also account for free gas.12PubMed. Numerical phase algorithm for decompression computers and application No dive computer eliminates risk entirely; they reduce it by translating complex gas physics into actionable guidance.
First Aid and Treatment
If decompression sickness is suspected, the single most important first-aid step is to get the diver breathing 100% oxygen at surface pressure as soon as possible. Normobaric oxygen has long been recognized as highly effective first aid, and it should begin at the dive site and continue during transport to a hyperbaric facility, a trip that often takes several hours.13PubMed. Normobaric oxygenation as a first-aid measure in decompression sickness Breathing pure oxygen helps in two ways: it speeds the elimination of nitrogen from the body, and it delivers more oxygen to tissues starved by bubble obstruction.
For most cases beyond mild altitude DCS, definitive treatment is hyperbaric oxygen therapy. The standard protocol used in the United States is often referred to as U.S. Navy Treatment Table 6 or an equivalent, in which the patient breathes 100% oxygen at about 2.8 atmospheres absolute inside a recompression chamber.14PubMed. Hyperbaric oxygen treatment for decompression sickness The elevated pressure shrinks existing bubbles, and the high oxygen concentration both accelerates nitrogen washout and helps heal damaged tissue. Many patients respond well after one session, but severe neurological cases sometimes require repeated treatments over days.
Delay matters. The sooner treatment begins, the better the outcome tends to be. Some diving destinations are remote, which is why organizations like Divers Alert Network (DAN) exist to help coordinate evacuations and locate the nearest recompression facility. Divers venturing into remote waters should carry an emergency action plan that includes contact numbers and the location of the nearest chamber.
Decompression Sickness Without Scuba Gear
The condition is not limited to scuba divers. Breath-hold divers, who carry no compressed gas at all, can develop a variant after repeated deep dives with short surface intervals. The syndrome has been called “Taravana,” a term originating from Polynesian pearl divers, and it presents as neurological symptoms after a series of deep free dives. The leading theory is that it represents a form of decompression sickness: nitrogen absorbed from the small amount of air in the lungs during repeated deep dives accumulates faster than the body can clear it between dives.15PubMed Central. Taravana syndrome and posterior reversible encephalopathy syndrome: a microbubble hypothesis for neurological accidents in breath-hold divers A systematic review identified 44 reported cases of decompression illness after breath-hold diving across the literature, confirming that while rare, it is a real hazard for competitive and occupational freedivers who push depth and repetition.16PubMed Central. The risk of decompression illness in breath-hold divers: a systematic review
Altitude exposure is the other major setting. Pilots of unpressurized aircraft, passengers in rapid decompression events, and astronauts transitioning from a pressurized habitat to a lower-pressure spacesuit all face DCS risk. In spaceflight, the design of the spacesuit itself is a key variable. Hybrid suits that combine gas pressure with mechanical counter-pressure can increase the total pressure on the body, reducing DCS risk or shortening the prebreathe period needed before a spacewalk.17PubMed Central. Revisiting decompression sickness risk and mobility in the context of the SmartSuit, a hybrid planetary spacesuit NASA’s protocols for extravehicular activity include lengthy oxygen prebreathing sessions to wash nitrogen out of the astronaut’s tissues before suit pressure drops.
How Marine Mammals Avoid the Bends
Whales and seals routinely dive to depths that would devastate a human diver, yet they were long thought to be essentially immune to decompression sickness. The reality is more nuanced. These animals have a suite of adaptations that dramatically reduce nitrogen loading. Their highly compliant lungs progressively collapse at depth, pushing air out of the gas-exchanging alveoli and into the reinforced upper airways where no gas transfer occurs. This lung collapse effectively shuts down nitrogen absorption partway through a deep dive.18PubMed Central. Pulmonary ventilation–perfusion mismatch: a novel hypothesis for how diving vertebrates may avoid the bends
Behavior plays a role too. Modeling work shows that the diving bradycardia marine mammals exhibit (a dramatic slowing of the heart rate during descent) combined with a reduced ascent rate and increased heart rate on the way up can lower mixed venous nitrogen pressure by as much as 45% compared to a scenario without those adjustments. Even modest reductions in inert gas load can cut DCS risk substantially.19PubMed. Deep diving mammals: Dive behavior and circulatory adjustments contribute to bends avoidance Still, evidence has accumulated in recent years that marine mammals are not fully immune. Sonar exposure and other disturbances that alter normal dive behavior have been linked to gas bubble lesions in stranded cetaceans, suggesting these animals operate with less margin than previously assumed.20PubMed Central. Deadly diving? Physiological and behavioural management of decompression stress in diving mammals
Long-Term Consequences
Most cases of decompression sickness, when treated promptly, resolve without lasting problems. But repeated or severe episodes can leave marks. Dysbaric osteonecrosis is a condition in which bone tissue dies, typically in the long bones near the shoulder or hip joints. It has long been recognized in commercial divers and compressed-air workers, and more recently in technical divers who accumulate substantial pressure exposure over time. Contributing factors include the frequency, duration, and depth of dives, inadequate decompression, prior DCS events, and increasing age.21PubMed Central. Dysbaric osteonecrosis in technical divers: The new ‘at-risk’ group? The condition can be painless and discovered incidentally on imaging, or it can progress to joint destruction requiring surgery.
Neurological residua from spinal cord DCS are another concern. Some divers recover incompletely, retaining subtle numbness, bladder dysfunction, or weakness. The extent of recovery depends heavily on how quickly treatment was started and how severe the initial insult was. These long-term risks are a major reason why diving medicine specialists emphasize conservative dive profiles and prompt treatment over a cavalier attitude toward minor symptoms.
Emerging Biomarkers and Research
One of the ongoing frustrations in diving medicine is that there is no simple blood test to diagnose decompression sickness. Diagnosis is clinical, based on symptoms and dive history. But researchers are making progress on biomarkers that could eventually help. A study of scuba divers found that circulating microparticles, tiny vesicular structures shed from activated cells, were between roughly 2 and 12 times higher in divers with DCS compared to asymptomatic divers matched for depth and breathing gas. Neutrophil activation showed a similarly strong association.22PubMed. Association of microparticles and neutrophil activation with decompression sickness These markers are not yet clinically actionable, but they point toward a future where an objective test could support or rule out a DCS diagnosis in ambiguous cases.
On the self-monitoring front, a study taught 41 recreational divers to use a portable audio Doppler device to listen for venous bubbles after dives. Roughly a third of dives produced detectable bubbles on echocardiography, and while the divers’ self-assessments were not precise enough for accurate grading, they could reliably pick up high bubble loads, the ones most associated with DCS risk.23PubMed Central. A Doppler ultrasound self-monitoring approach for detection of relevant individual decompression stress in scuba diving The idea is appealing: if you could check your own bubble status after a dive, you could adjust your next dive accordingly, adding a personalized layer to what dive computers already do.
Gas Switching in Technical and Commercial Diving
Technical and commercial divers routinely breathe gas mixtures containing helium instead of, or in addition to, nitrogen. Helium is used because it is less narcotic at depth and diffuses faster than nitrogen. But switching between gases at depth introduces its own complexity. Animal research has shown that the risk of DCS after a gas switch depends on both how quickly the new gas equilibrates in tissue and the inherent potency of each gas for causing bubble problems. Helium is less potent than nitrogen, and nitrogen less potent than argon, but their exchange rates differ in a different order. This means that total inert gas pressure in tissue can transiently rise during a switch yet DCS risk can still decline, because the new gas is less likely to form harmful bubbles.24PubMed. Effect of inert gas switching at depth on decompression outcome in rats Understanding these counterintuitive dynamics is critical for anyone planning mixed-gas dives, and it illustrates why decompression planning in technical diving remains as much art as science.
Pharmacological approaches to reducing DCS risk have also been explored, though none are ready for routine use. Antioxidants like vitamin C and N-acetylcysteine were tested in a diving simulation model to see if they could blunt the oxidative stress that accompanies bubble formation. While NAC partially preserved glutathione levels (an indicator of antioxidant capacity), neither supplement prevented DCS in the study animals, suggesting oxidative stress alone is not the sole trigger.25PubMed. Antioxidants, endothelial dysfunction, and DCS: in vitro and in vivo study A more recent study tested a ketone ester supplement in rats and found it improved blood oxygen levels and reduced inflammatory markers after decompression, though its effect on bubble load did not reach statistical significance.26PubMed. The protective effects of 1,3-butanediol acetoacetate diester on decompression sickness in rats These are early-stage results in animals, not recommendations, but they hint at future adjuncts to the purely physical strategies divers rely on today.
The Caisson Workers Who Named the Disease
Long before recreational scuba existed, the condition was killing and crippling bridge builders. In the 1860s and 1870s, workers constructing the Eads Bridge in St. Louis and the Brooklyn Bridge in New York labored inside caissons, pressurized chambers sunk into riverbeds to allow excavation below the waterline. When workers returned to normal atmospheric pressure after shifts in these chambers, many collapsed with joint pain, paralysis, or worse. The physicians assigned to these projects, Dr. Alphonse Jaminet at the Eads Bridge and Dr. Andrew Smith at the Brooklyn Bridge, documented hundreds of cases and experimented with countermeasures, including limiting shift lengths and slowing the rate of decompression.27PubMed. Caisson disease during the construction of the Eads and Brooklyn Bridges: A review Smith combined his physiological observations with a review of existing engineering and medical literature to describe what he called “Caisson Disease” and to devise strategies to reduce its effects.28PubMed. The Laryngologist Who Saved the Brooklyn Bridge Their work, painstakingly assembled from thousands of casualties, laid the foundation for modern decompression theory and treatment.29PubMed Central. Discovery of caisson disease: a dive into the history of decompression sickness The workers’ characteristic stiff-legged gait as they emerged from the caissons reportedly inspired the slang term “the bends,” a name that stuck and is still used casually more than 150 years later.