Caisson disease is an older name for decompression sickness, a condition where nitrogen gas dissolved in your blood and tissues forms bubbles when pressure around the body drops too quickly. You might also hear it called “the bends.” It affects scuba divers, underwater construction workers, and anyone who moves rapidly from a high-pressure environment to a lower-pressure one. The overall incidence among recreational divers is about 3.4 per 10,000 dives, according to the Divers Alert Network, though rates vary widely depending on the type of diving.
Where the Name Comes From
The term “caisson disease” traces back to 1840, when a French engineer named Charles-Jean Triger used compressed air to mine coal in the Loire Valley. He worked inside a pressurized chamber he called a caisson, French for “box.” After returning to the surface, Triger and two of his workers experienced joint pain, soreness, and temporary breathlessness roughly 30 minutes later. He described the condition as “mal de caisson,” making this the first recorded case of what we now call decompression sickness.
The condition gained wider attention during major construction projects in the United States. In the summer of 1868, Captain James Buchanan Eads began building a 1,500-foot bridge across the Mississippi River in St. Louis. Workers descended into caissons pushed deep into the riverbed. No injuries were reported until the caissons reached about 60 feet, roughly half the depth needed to hit bedrock at 100 feet. At that depth, workers began developing crippling pain and other mysterious symptoms after surfacing. Physicians studying these workers over the following decades gradually pieced together what was happening inside their bodies, connecting the symptoms to rapid pressure changes.
How Nitrogen Bubbles Form
The mechanism behind caisson disease is straightforward once you understand how gases behave under pressure. When you breathe air at higher-than-normal pressure, whether underwater or inside a pressurized work chamber, your blood and tissues absorb extra nitrogen. The deeper you go, the more nitrogen dissolves into your body. This is perfectly fine as long as the pressure stays constant.
The problem starts when pressure drops. If you ascend slowly, your body has time to release that extra nitrogen back through your lungs gradually, the same way it entered. But if the pressure drops too fast, the nitrogen can’t escape through normal breathing quickly enough. Instead, it comes out of solution right where it is, forming gas bubbles in your blood vessels, joints, muscles, spinal cord, and other tissues. Think of it like opening a carbonated drink: the dissolved gas stays put under pressure, but release that pressure suddenly and bubbles appear everywhere.
Symptoms by Severity
Decompression sickness is typically divided into two types based on which parts of the body are affected.
Type I involves the musculoskeletal system and skin. The hallmark symptom is deep, aching joint pain, most commonly in the shoulders, elbows, and knees. This is where the nickname “the bends” comes from: workers on the St. Louis Bridge would double over in pain. You might also notice skin mottling, itching, or a rash. Type I symptoms are painful and disruptive but generally not life-threatening on their own.
Type II is more serious. Bubbles form in or travel to the spinal cord, brain, or lungs. Neurological symptoms can include numbness, tingling, muscle weakness, difficulty walking, dizziness, vision changes, confusion, and in severe cases, paralysis. When bubbles affect the lungs, they can cause chest pain, coughing, and difficulty breathing. Symptoms of either type usually appear within a few hours of surfacing, though they can occasionally be delayed up to 24 hours.
Who Is at Higher Risk
Not everyone exposed to the same pressure profile gets decompression sickness, and researchers have identified several factors that affect individual susceptibility. Analysis of dive data collected by DAN Europe found that older divers face higher risk, with the average age among DCS cases being 42 compared to 37 in the general diving population. Higher body fat percentage is another significant factor. DCS cases had an average body fat of about 34%, compared to roughly 24% in unaffected divers. Because nitrogen is more soluble in fat than in lean tissue, people carrying more body fat absorb and retain more nitrogen during a dive.
Women appear to have a higher likelihood of developing DCS than men, even when bubble formation is similar between the two groups. Heavy physical exertion before a dive and high workload during a dive both significantly increase risk. Dehydration, fatigue, and cold water exposure are also commonly cited contributing factors, though they are harder to quantify precisely.
How It Differs From an Arterial Gas Embolism
Caisson disease is sometimes confused with arterial gas embolism, another pressure-related diving injury. Both involve gas bubbles in the body, but they arise through different mechanisms. In decompression sickness, bubbles form gradually in tissues and veins as dissolved nitrogen comes out of solution. In an arterial gas embolism, air enters the arterial bloodstream directly, usually because expanding gas in the lungs ruptures tiny air sacs during a rapid ascent. An arterial gas embolism tends to cause sudden, dramatic symptoms (often stroke-like) immediately upon surfacing, while DCS symptoms typically build over minutes to hours. Despite these differences, the treatment for both conditions is essentially the same.
Treatment With Recompression
The standard treatment for decompression sickness is hyperbaric oxygen therapy, sometimes called recompression. You’re placed inside a sealed chamber where the pressure is increased, typically to about 2.8 times normal atmospheric pressure. This does two things: the higher pressure physically shrinks the nitrogen bubbles, and breathing pure oxygen at that pressure helps your body flush nitrogen out of tissues much faster than it could on its own.
A typical session follows a structured protocol. The most commonly used one involves pressurization with alternating periods of breathing pure oxygen and brief air breaks to reduce the risk of oxygen-related side effects. The total treatment time runs roughly 4.5 to 5 hours for a standard session. Some cases resolve after a single treatment; others, particularly those involving neurological symptoms, may need multiple sessions over several days. The sooner treatment begins after symptoms appear, the better the outcome tends to be.
As a first-aid measure before reaching a hyperbaric facility, breathing 100% oxygen at the surface helps by creating a larger pressure difference between the nitrogen in your tissues and the gas you’re breathing, which speeds up nitrogen elimination even without recompression.
Long-Term Effects
Most people who receive prompt treatment recover fully, but repeated or severe episodes of decompression sickness can cause lasting damage. One well-documented long-term complication is a form of bone death in which nitrogen bubbles damage the blood supply to bones, particularly around the hips and shoulders. This was historically common among caisson workers and commercial divers who experienced repeated pressure exposures over years. Neurological damage from spinal cord involvement can also persist if treatment is delayed, leading to chronic weakness, numbness, or bladder problems.
Prevention
Modern diving practices are built around preventing exactly what those 19th-century bridge workers experienced. The most important factor is controlling how fast pressure changes. Current guidelines from the U.S. Navy and NOAA recommend ascending no faster than 30 feet per minute. Recreational dive training agencies allow rates between 30 and 60 feet per minute, though slower is generally safer. Safety stops, where you pause your ascent for several minutes at a shallow depth, give your body extra time to off-gas nitrogen in the zone where pressure changes are most dramatic.
Dive computers and decompression tables calculate how long you can safely stay at a given depth based on the physics of nitrogen absorption. Staying well within these limits, staying hydrated, avoiding strenuous exercise right before diving, and spacing dives far enough apart to allow full nitrogen clearance all reduce your risk substantially. For workers in pressurized environments like tunnels or caissons, the same principles apply: controlled, gradual decompression is the key to getting back to the surface safely.