Every diver hears about it during open water training, but few of us truly sit down and unpack it. Decompression sickness is one of those topics that gets a quick slide in a classroom, a nervous joke on the boat, and then rarely a proper conversation. That is a shame, because understanding how it actually works is one of the most empowering things a diver can do. It shifts you from being afraid of the bends to being genuinely prepared for them.
In this guide we will walk through what happens inside the body during a dive, why bubbles form, how to spot the earliest signs, and what to do if something feels off after surfacing. Whether you are a new open water diver, a technical diver logging long deco stops, or a divemaster running trips every week, this is worth the read.
Let’s take a look at the science, the symptoms, the treatment pathway, and the daily habits that keep DCS off your logbook.
What Decompression Sickness Actually Is
Decompression sickness, commonly called DCS or the bends, is an injury caused by dissolved inert gas, usually nitrogen, coming out of solution inside the body during or after an ascent. At depth, the increased pressure forces more nitrogen from the breathing gas into our tissues and blood. As long as pressure stays high, that nitrogen sits quietly dissolved. Ascend too quickly, and it does not have time to leave the body gradually through the lungs.
Instead, it forms bubbles. Those bubbles can lodge in joints, block small vessels, irritate the spinal cord, or travel through a patent foramen ovale into arterial circulation. Where they end up determines what kind of DCS a diver experiences.
It helps to think of a bottle of sparkling water. Sealed, the gas stays invisible. Crack the cap slowly, and the pressure releases gently. Crack it fast, and bubbles erupt everywhere. Our bodies are not that different, only far more delicate and far less forgiving.
Type 1 and Type 2 DCS
Historically, doctors have divided DCS into two broad categories. Type 1 refers to milder cases involving joint pain, skin symptoms, and lymphatic swelling. Type 2 refers to more serious cases involving the nervous system, the inner ear, the lungs, or the cardiovascular system.
In practice, this distinction can be misleading. What looks like a sore shoulder after a dive can hide neurological involvement. That is why any post dive symptom, even a subtle one, deserves attention rather than a shrug.
How It Differs From Arterial Gas Embolism
DCS and arterial gas embolism, or AGE, are both grouped under the umbrella of decompression illness. AGE happens when a diver holds their breath during ascent or has lung overexpansion, forcing gas directly into arterial circulation. It is usually immediate and dramatic. DCS, by contrast, can appear minutes or hours after surfacing. The treatments overlap, but the causes are different, and knowing which is which helps emergency responders act faster.
What Causes Bubbles to Form
The short answer is pressure change over time. The longer answer involves a mix of physics, physiology, and personal factors that vary between divers, and even between dives on the same person.
Ascent Rate
Ascending too quickly is the classic trigger. Modern dive computers cap ascent rate at around 9 to 10 meters per minute, and many experienced divers go slower. A rushed ascent, even from a shallow dive, does not give tissues time to offgas properly through the lungs.
Depth and Bottom Time
Deeper dives load more nitrogen into tissues, and longer dives give that gas more time to saturate. This is why dive tables and computer algorithms exist. They estimate how much nitrogen your tissues have absorbed and how long it will take to safely release.
Repetitive Dives
Nitrogen does not fully clear between dives on the same day. Each subsequent dive starts with residual gas already dissolved in tissues. This is why the second and third dives of the day carry more risk, and why multiday liveaboards demand careful planning.
Personal Risk Factors
Two divers can follow identical profiles and have very different outcomes. Factors that raise personal risk include:
- Dehydration, which thickens blood and slows gas exchange
- Fatigue and poor sleep the night before
- Alcohol consumption before or after diving
- Cold water exposure, which affects circulation
- Heavy exertion during or immediately after a dive
- Body composition, since nitrogen is more soluble in fatty tissue
- Age and general cardiovascular health
- A patent foramen ovale, a small opening between heart chambers present in around a quarter of the population
None of these guarantee DCS. They simply tilt the odds, sometimes noticeably.
Flying After Diving
Cabin pressure at cruising altitude is lower than at sea level, effectively continuing an ascent. Flying too soon after diving is a common cause of DCS in travelers who otherwise had uneventful dives. The general guidance is a minimum of 12 hours after a single no deco dive and 18 to 24 hours after multiple dives or any deco diving.
Recognizing the Symptoms
Symptoms can appear during ascent, shortly after surfacing, or up to 24 to 48 hours later. Most cases show up within the first six hours. Recognizing them early makes an enormous difference to outcomes.
Common Early Signs
- Unusual fatigue that feels heavier than a normal post dive tiredness
- Joint pain, most often in the shoulders, elbows, hips, or knees
- Skin itching, rashes, or a mottled marbled appearance on the torso
- Headache or a foggy, unfocused feeling
- Tingling or numbness in the arms, legs, or torso
- Dizziness or a sense of imbalance
More Serious Signs
- Weakness or paralysis in a limb
- Difficulty walking or coordinating movement
- Loss of bladder or bowel control
- Chest pain, coughing, or shortness of breath
- Hearing loss, ringing in the ears, or severe vertigo
- Confusion, slurred speech, or changes in personality
- Loss of consciousness
A diver with any neurological, cardiovascular, or inner ear symptoms should be treated as a medical emergency, no exceptions. If in doubt, treat it as DCS until a physician says otherwise. Divers and buddies often talk themselves out of calling for help because the symptoms feel embarrassing or vague. That hesitation is exactly what makes mild cases turn into severe ones.
The “I Am Just Tired” Trap
Ask any hyperbaric doctor about missed DCS, and they will describe the same pattern. The diver felt off after the dive, chalked it up to a long day, took a nap, and woke up worse. Post dive fatigue is normal. Post dive fatigue combined with any of the symptoms above is not. When something feels different from your usual tiredness, take it seriously.
What to Do If You Suspect DCS
Speed matters. The earlier a diver receives oxygen and hyperbaric treatment, the better the odds of a full recovery. Here is the practical response chain most training agencies teach.
1. Get the Diver Out of the Water Safely
Do not attempt in water recompression unless you are part of a formal technical team trained and equipped for it. For recreational divers, the answer is simple: get them onto the boat or shore, calm and horizontal.
2. Administer 100 Percent Oxygen
Emergency oxygen is the single most important field treatment for DCS. It helps flush nitrogen from tissues and improves oxygen delivery to areas affected by bubbles. Every dive boat should carry a working oxygen unit, and every dive professional should know how to use it. If you are not oxygen trained, take the course. It is short, affordable, and genuinely lifesaving.
3. Keep the Diver Hydrated and Comfortable
If the diver is conscious and able to swallow, offer water or a non caffeinated drink. Keep them warm but not overheated. Lay them flat on their back if they can tolerate it.
4. Call for Help
Contact the local emergency number, a diving emergency hotline, and the nearest hyperbaric facility. Provide the dive profile, symptoms, timeline, and the diver’s medical background. Do not wait to see if symptoms improve. Even if they do, a physician needs to make the call about treatment.
5. Arrange Transport
This is where logistics can quickly become overwhelming, especially in remote destinations. Evacuation from a liveaboard or an island dive site often involves a boat transfer, an ambulance, and sometimes a specialized medical flight. Costs can climb into the tens of thousands within hours. This is exactly the moment when our dive accident coverage matters. At DiveAssure we handle the calls, coordinate the chamber, and cover the treatment so the diver and their family can focus on recovery. You can read a real account of how this played out in a diving accident in Belize, where fast coordination made all the difference.
Hyperbaric Treatment: What Actually Happens
The definitive treatment for DCS is recompression in a hyperbaric chamber. Understanding what happens inside can take some of the mystery and fear out of the process.
Recompression
The chamber pressurizes to a depth equivalent, most commonly around 18 meters, sometimes deeper. This reduces bubble size, forces gas back into solution, and improves circulation to affected tissues.
Oxygen Breathing
The diver breathes 100 percent oxygen through a mask at intervals, with short air breaks to reduce oxygen toxicity risk. This creates a strong pressure gradient that drives nitrogen out of the body.
Slow Decompression
The chamber then decompresses slowly over several hours, following a treatment table such as US Navy Table 6. A single treatment often lasts around five hours. Some cases require multiple treatments over several days.
Recovery
Most divers who receive prompt treatment recover fully. Delayed treatment can leave residual symptoms, particularly with neurological DCS. This is one more reason not to tough it out and hope it passes.
Preventing DCS on Every Dive
The best treatment is not needing treatment. Prevention is not glamorous, but it is where experienced divers separate themselves from casual ones.
Dive Conservatively
Stay well within your no decompression limits. Add a safety stop to every dive, even shallow ones. Set your computer to a conservative setting if it offers one. There is no medal for surfacing with zero minutes of no deco time remaining.
Master Your Ascent
Slow, controlled ascents are non negotiable. Aim for around 9 meters per minute or slower in the last portion. Good ascent control is directly tied to good buoyancy, which is why we always come back to the importance of good buoyancy as a foundational skill.
Plan Your Day, Not Just Your Dive
Repetitive dives, surface intervals, and multiday profiles all matter. Space your dives out. Go shallower on later dives. Skip the last dive if you are feeling depleted. Long surface intervals are cheap insurance.
Hydrate, Rest, and Eat Well
Start the day hydrated. Keep drinking between dives. Sleep properly the night before. Skip the beers until the diving is done for the day. These sound obvious, but they are the habits that quietly separate long careers from cut short ones.
Know Your Personal Limits
If you have a cold, a recent injury, jet lag, or simply a bad feeling, sit the dive out. No site is worth pushing through a body that is telling you no. Follow the basic essential diving rules that we all learned early, and revisit them often.
Plan for Flying and Altitude
Build a proper buffer before flying home or driving over mountain passes. When in doubt, add hours rather than shave them.
Consider a PFO Screening
If you have had an unexplained DCS hit, especially a skin or neurological one, ask a diving medicine specialist about screening for a patent foramen ovale. It is not a decision to make casually, but it can change how you approach diving going forward.
Packing Tips and Pro Tips
A few practical habits that experienced divers build into their routine.
- Carry your own oxygen kit on remote or private trips when possible
- Keep a copy of your dive accident coverage details and emergency numbers in your phone and in your dry bag
- Log your dives properly, including any small anomalies, so patterns become visible over time
- Refresh your rescue and oxygen provider training every couple of years
- Talk about DCS openly with your buddies before the dive, not after something goes wrong
- Know where the nearest chamber is before you get in the water, especially in remote destinations
Preparation is not paranoia. It is what lets you relax and enjoy the dive, because you know you have already handled the “what ifs.” For a deeper look at planning ahead, our guide on diving emergency preparedness is worth bookmarking.
Where DiveAssure Fits Into the Picture
No amount of good technique makes a diver immune to decompression illness. Bodies are variable, conditions change, and sometimes DCS shows up on a profile that looked perfectly safe. What we can control is what happens next.
At DiveAssure we built our coverage around the reality of how dive accidents unfold. That means hyperbaric chamber treatment, emergency evacuation from remote sites, medical transport home when needed, and 24 hour support for divers and their families. We cover recreational, technical, and professional divers, because DCS does not care what card is in your wallet. Need coverage for your upcoming trip? Get covered here.
Conclusion
Decompression sickness is not a mysterious force that strikes at random. It is a physiological process we can understand, plan for, and largely prevent. The divers who take it seriously without becoming afraid of it are the ones who dive the longest and enjoy it the most. Learn the science, respect the ascent, hydrate like a professional, and never talk yourself out of asking for help when something feels wrong.
Happy diving, and may your next adventure be your best one yet!
Summary
Decompression sickness happens when nitrogen absorbed at depth forms bubbles in the body during ascent, causing symptoms that range from joint pain and fatigue to neurological issues. Prevention comes down to slow ascents, safety stops, conservative dive profiles, good hydration, and honest self-assessment. If symptoms appear, breathe emergency oxygen, contact a hyperbaric facility, and arrange transport quickly. At DiveAssure we provide dive accident coverage that includes emergency evacuation and chamber treatment, so divers can focus on the dive rather than the worst case scenario.