Decompression Sickness Explained Symptoms Causes Prevention and Treatment
- R Sanchez
- Aug 8
- 9 min read
A diver can surface feeling fine, rinse gear, laugh with friends, and only later notice a deep ache in the shoulder or a strange tingling in the feet. That delay is one reason decompression sickness can be so dangerous. It does not always announce itself underwater. It can appear minutes to hours after a dive, and in serious cases, it can affect the brain, spinal cord, lungs, skin, joints, or inner ear.
Decompression sickness, often called “the bends,” is a medical emergency linked to pressure changes. It is best known among scuba divers, but it can also affect people in other settings, including commercial divers, caisson workers, aviators, astronauts, and anyone exposed to major pressure shifts.
This article is for general education only and is not a substitute for medical care. If decompression sickness is possible, seek emergency medical help right away.
What decompression sickness is
The air we breath from our tanks consists of 21% Oxygen and 79% Nitrogen. Decompression sickness occurs when dissolved gases, mainly nitrogen, form bubbles in the body after a drop in surrounding pressure.
Henry's Law states that higher surrounding pressure forces more nitrogen gas to dissolve into a diver's bloodstream and tissues.
Here is the simple version. When someone dives, water pressure increases with depth. Under that pressure, the body absorbs more nitrogen from the breathing gas. During a slow, controlled ascent, the body releases that nitrogen gradually through the lungs.
If the pressure drops too quickly, nitrogen can come out of solution too fast. Think of opening a soda bottle. While sealed, gas stays dissolved in the liquid. When the cap comes off, pressure drops and bubbles appear. In the body, those bubbles can irritate tissues, block blood flow, trigger inflammation, and interfere with nerve function.
Decompression sickness is not the same as lung overexpansion injury or arterial gas embolism, though they can happen in related diving situations and may look similar. Both require urgent care. From a practical standpoint, anyone with symptoms after diving should treat the situation seriously and get evaluated.
How decompression sickness happens
Most recreational dives end safely. Modern dive computers, tables, training, and conservative habits have reduced risk. Still, decompression sickness can occur even when a diver believes they followed the rules.
The risk rises when the body takes on more nitrogen than it can release safely during ascent. This can happen with:
Deep dives
Greater depth means greater pressure and more nitrogen absorption.
Long bottom times
The longer a diver stays at depth, the more inert gas can build up.
Rapid ascents
Fast pressure change gives nitrogen less time to leave the body safely.
Repeated dives
Nitrogen can remain in the body between dives, especially during multi-dive days.
Skipped safety stops
A safety stop gives the body extra time to release nitrogen before surfacing.
Flying too soon after diving
Cabin pressure in an aircraft is lower than sea-level pressure, which can promote bubble formation after a dive.
Decompression sickness can also occur outside recreational scuba. Workers in compressed-air environments, such as tunneling or bridge construction, may face pressure shifts. High-altitude exposure after diving can add risk. In aviation, rapid ascent or cabin pressure problems can also create conditions for bubble formation.
Symptoms can be mild, severe, or easy to miss
Symptoms vary because bubbles can affect different parts of the body. Some cases start subtly. Others become serious quickly.
Common symptoms include:
Symptom area | What it may feel or look like |
Joints and muscles | Deep aching pain, often in shoulders, elbows, knees, or ankles |
Skin | Itching, rash, mottled or marbled skin, swelling |
Nervous system | Numbness, tingling, weakness, trouble walking, dizziness, confusion |
Inner ear | Vertigo, nausea, hearing changes, balance problems |
Lungs | Chest pain, cough, shortness of breath |
General symptoms | Fatigue, headache, unusual weakness, feeling “off” after a dive |
Joint pain is the classic symptom that gave “the bends” its name. A diver might feel a dull, deep pain that does not match a sprain or strain. Skin changes can look like a rash or a marbled pattern. Neurologic signs, such as weakness, bladder problems, confusion, or trouble speaking, are especially concerning.
Timing matters, but it is not always predictable. Symptoms often appear within a few hours after surfacing. They may also occur later. A diver who feels unusually tired after a dive should not dismiss it automatically as a normal post-dive feeling, especially if other symptoms appear.
A realistic example shows why small signs matter
Consider a recreational diver on a weekend trip. They complete two dives in one morning. The first dive is deeper than planned, and the second is shallower but still a decent length. The diver follows the group back to the surface and remembers doing a short safety stop, though the ascent near the end feels rushed because the boat is drifting.
After lunch, they notice shoulder pain. They assume it came from lifting tanks. An hour later, tingling spreads into one hand. By evening, they feel weak and slightly unsteady.
This is the kind of case where waiting can cause harm. The symptoms might be from something minor, but after recent diving, decompression sickness must stay high on the list. Calling emergency medical services, contacting a dive medical hotline if available, and getting to a facility that can coordinate hyperbaric treatment may make a major difference.
A second example looks different. A diver makes several easy shallow dives over two days, drinks little water, skips sleep, and flies home the next morning. During the flight, they develop unusual fatigue, knee pain, and a patchy skin rash. The dives were not extreme, but the stack of risk factors matters.
These examples are not meant to scare responsible divers away from the water. They show how decompression sickness often comes from a chain of decisions and conditions, not one dramatic mistake.
Risk factors that raise the chances of decompression sickness
No single factor guarantees decompression sickness, and no checklist can remove risk completely. Still, certain conditions make it more likely.
Dive profile and ascent behavior
Depth, duration, ascent rate, and surface intervals play a central role. Repetitive dives, multi-day dive trips, cold-water dives, and heavy exertion underwater can all increase stress on the body.
A dive that stays within computer limits can still carry risk if the diver ascends too quickly, ignores warnings, or treats no-decompression limits as targets rather than boundaries.
Physical condition and hydration
Dehydration may reduce the body’s ability to manage circulation and gas elimination. Alcohol use, vomiting, diarrhea, heat exposure, and inadequate fluids can all contribute.
Fatigue can also cloud judgment. A tired diver may miss a computer alert, skip a safety stop, or fail to recognize symptoms after surfacing.
Cold, exertion, and stress
Cold can change blood flow and increase workload. Heavy finning against current or carrying gear in rough conditions may increase gas uptake and fatigue.
Stress also matters. A diver who feels anxious may breathe more rapidly, burn through gas, and make rushed decisions.
Individual health factors
Some health factors may increase risk or complicate symptoms. These can include obesity, poor cardiovascular fitness, older age, prior decompression sickness, and certain heart or lung conditions.
A patent foramen ovale, or PFO, is a small opening between the upper chambers of the heart that remains from fetal circulation. Many people do not know they have one. In some divers, a PFO may allow bubbles to bypass the lungs and enter arterial circulation, which can raise concern after unexplained neurologic decompression illness.
Anyone with a history of decompression sickness, fainting episodes, unexplained neurologic symptoms after diving, or significant heart or lung disease should speak with a clinician familiar with dive medicine before returning to diving.
Prevention starts before the dive
Good prevention is practical. It is not about being fearful. It is about making conservative choices before, during, and after a dive.
Plan the dive and stay within limits
Use a dive computer or dive tables properly. Know the planned maximum depth, bottom time, ascent rate, and required stops before entering the water.
Good habits include:
Check your computer before and during the dive
Follow the most conservative computer if buddy computers differ
Avoid pushing no-decompression limits
Build in a slow ascent
Complete a safety stop when conditions allow
End the dive with enough gas for a calm ascent
Ascend slowly and respect safety stops
A controlled ascent gives nitrogen time to leave the body through normal breathing. Many training agencies teach a slow ascent rate and recommend a safety stop near the end of many dives, often around 15 feet for several minutes. Follow your training, your computer, and local dive guidance.
If conditions make a stop difficult, such as strong current or rough seas, that risk should influence future dive planning. Conservative divers account for real-world conditions, not just the numbers on a screen.
Manage repetitive diving carefully
Multi-dive days and dive vacations require extra care. Nitrogen can carry over from one dive to the next.
Smart choices include:
Take longer surface intervals when possible
Make the deepest dive first when planning allows
Reduce depth and time later in the day
Add rest days during heavy dive trips
Avoid intense exercise right after diving
Wait before flying or going to altitude
Flying after diving is a well-known risk because aircraft cabins have lower pressure than sea level. Many dive organizations recommend waiting after diving before flying, with longer waits after multiple dives or decompression dives. Follow your training agency’s current guidance, your dive operator’s advice, and your computer’s no-fly recommendation when available.
Driving to altitude after diving can raise similar concerns. Mountain roads, high-elevation resorts, and helicopter travel may all matter.
Take care of your body
Before diving, get adequate rest, hydrate, and avoid alcohol. Stay warm during and after dives. Do not dive when sick, congested, unusually fatigued, or impaired.
Fitness helps, but intense workouts right before or soon after diving may not be wise. Gentle movement is different from heavy exertion. When in doubt, choose the more conservative option.
What to do if decompression sickness is suspected
Do not try to “walk it off.” Do not get back in the water to recompress unless directed by trained professionals in a controlled setting. In-water recompression carries serious risks and is not appropriate for recreational self-treatment.
If symptoms appear after diving:
Stop diving immediately
Do not make another dive to see if symptoms improve.
Call emergency medical services
Tell them the person recently dived and may have decompression sickness.
Give 100% oxygen if trained and equipped
Emergency oxygen can help reduce bubble size and improve oxygen delivery to tissues.
Keep the person lying comfortably
Protect them from heat loss or overheating. Do not force unnecessary activity.
Provide fluids if the person is awake and able to swallow
Use plain water or an oral rehydration drink. Do not give alcohol.
Contact dive medical support
In the United States, many divers know to contact Divers Alert Network for guidance, while still activating emergency services first when symptoms are serious.
The key is fast evaluation. Mild symptoms can progress. Neurologic symptoms deserve urgent attention.
Treatment usually centers on oxygen and recompression
The main treatment for significant decompression sickness is recompression therapy in a hyperbaric chamber. The chamber increases pressure around the body, which helps shrink gas bubbles. The person breathes oxygen under medical supervision, which helps remove nitrogen and support affected tissues.
Treatment may also include:
High-flow oxygen before and during transport
Medical evaluation for neurologic, lung, skin, or joint symptoms
IV fluids if needed
Monitoring for changes in strength, sensation, balance, breathing, and mental status
Repeat hyperbaric treatments in some cases
The exact treatment plan depends on symptoms, timing, exam findings, and access to specialist care. A local emergency department may not have a hyperbaric chamber on site, but clinicians can stabilize the patient and coordinate transfer when needed.
Early treatment often improves the chance of recovery. Delays can increase the risk of lasting problems, especially when the nervous system is involved.
Returning to diving needs medical guidance
After suspected or confirmed decompression sickness, the question is not just “When do symptoms stop?” It is also “Why did this happen, and how can risk be reduced next time?”
A dive medicine specialist may review the dive profile, computer data, symptoms, treatment, and health history. They may recommend waiting before returning to diving, further testing, changes in dive habits, or avoiding certain dive profiles.
For someone who loves diving, this can feel frustrating. Still, a careful return plan protects both the diver and their buddy. Diving after incomplete recovery or without understanding the cause can put a person at risk for another event.
The main takeaway
Decompression sickness is caused by gas bubbles that form when pressure drops too quickly after exposure to higher pressure. It can cause joint pain, skin changes, dizziness, weakness, numbness, breathing problems, confusion, and severe neurologic symptoms.
The best defense is conservative diving: plan well, ascend slowly, respect safety stops, manage repetitive dives, stay hydrated and rested, and wait before flying or going to altitude. If symptoms appear after a dive, treat them as urgent. Get medical help, use emergency oxygen if available and trained to do so, and seek evaluation for hyperbaric treatment.
A beautiful dive should end with a safe surface interval, not a gamble. When something feels wrong after pressure exposure, act early. That choice can protect health, mobility, and future time in the water.
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