---
title: "Decompression Sickness (DCS): Causes, Symptoms, Prevention"
description: "Decompression sickness (the bends): what causes it, the symptoms, Type I vs Type II, first aid and treatment, and how divers prevent it."
canonical: "https://donarundas.com/depth-notes/safety/decompression-sickness"
author: "Donarun Das — TDI Trimix Instructor, KISS Sidewinder CCR Instructor"
category: "safety"
published: "2026-06-16"
tags: ["decompression-sickness", "dcs", "the-bends", "dive-safety", "dive-medicine"]
disclaimer: "Dive theory published by a working instructor for education. It is not medical advice and not a substitute for training. Decompression, gas, and depth decisions belong with your own training, your dive computer, and a dive medical officer."
license: "© Donarun Das. Quote with attribution and a link to the canonical URL."
---

# Decompression Sickness (DCS): Causes, Symptoms, Prevention

## Type I vs Type II

Clinicians split DCS into two buckets, and the difference matters because it changes how urgently you act.

| | Type I (milder) | Type II (serious) |
|---|---|---|
| Affects | joints, limbs, skin, lymphatics | nervous system, inner ear, heart/lungs |
| Typical signs | dull joint or limb pain, blotchy/itchy skin, fatigue | numbness, tingling, weakness, balance or vision changes, confusion, breathing difficulty |
| Urgency | still needs assessment | medical emergency |

### Type I, in more detail
- **Musculoskeletal ("pain-only" bends):** a deep, dull ache, classically in a shoulder or elbow, that's hard to pin to one spot and doesn't change much when you move the joint. The most common presentation.
- **Skin (cutaneous) DCS:** itching, or a mottled, marbled purple rash called *cutis marmorata*. It looks minor, but a marbled rash can be the visible edge of a heavy bubble load, so it's a reason to watch closely, not shrug off.
- **Lymphatic:** localised swelling and a heavy, puffy feeling as bubbles block lymph drainage.
- **Unusual fatigue:** wipe-out tiredness beyond what the dive should cause. Normal post-dive tiredness is covered in [post-dive fatigue](https://donarundas.com/depth-notes/physiology/post-dive-fatigue); the concern is when it's out of proportion or comes with anything else on this list.

### Type II, in more detail
- **Spinal cord DCS:** the most common serious form in divers. Low-back or girdling pain, then numbness, tingling, leg weakness, an unsteady walk, and sometimes bladder trouble. Easy to dismiss early, dangerous to ignore.
- **Cerebral DCS:** headache, confusion, personality change, visual disturbance, or one-sided weakness.
- **Inner-ear (vestibular) DCS:** vertigo, nausea, ringing, or hearing loss. More common after deeper, mixed-gas dives and around helium-to-nitrox switches. It can be mistaken for inner-ear barotrauma, which needs different treatment.
- **Cardiopulmonary ("the chokes"):** chest pain, a dry cough, and breathlessness when a large bubble load hits the lungs. Rare, but a genuine emergency.

## Symptoms and when they show

- Joint or limb pain, often the shoulder or elbow
- Unusual, heavy fatigue out of proportion to the dive
- Skin itching or a marbled (cutis marmorata) rash
- Tingling, numbness, or weakness
- Dizziness, vertigo, or hearing changes
- Difficulty walking, confusion, or trouble breathing

Onset is usually quick: around half of cases show within the first hour or two, and the large majority within 24 hours of surfacing. Delayed onset happens, and **flying too soon can trigger or worsen it**, which is why no-fly times exist. Anything that starts or worsens after a dive deserves suspicion, especially anything focal or neurological.

## How it's diagnosed

There's no blood test or scan that confirms DCS. It's a *clinical* diagnosis: the doctor weighs your dive profile, the timing, and the symptoms. Because there's no confirmatory test and the cost of waiting is high, the rule is to treat on reasonable suspicion rather than hold out for certainty. The main thing to tell apart is [arterial gas embolism](https://donarundas.com/depth-notes/safety/pulmonary-barotrauma-a-g-e), which comes on within minutes of surfacing with stroke-like signs, often after a breath-hold ascent. The first aid is the same either way.

## First aid and treatment

The emergency steps are in the box at the top of this page, and on our printable [dive emergency action card](https://donarundas.com/tools/dive-emergency-card) for your save-a-dive kit. Here's why they work and what happens next.

- **Oxygen** is the single most useful field treatment. Breathing 100% O₂ steepens the gradient that pulls inert gas out of the bubbles and speeds their shrinking, and it oxygenates tissue starved by blocked vessels. Give it continuously, even if symptoms ease, and don't delay it (or evacuation) just to position the diver.
- **Fluids** help, since immersion and diving leave most divers mildly dehydrated, which thickens the blood around bubbles.
- **Recompression** is the definitive treatment: in a hyperbaric chamber the diver is taken back "down" under pressure to crush the bubbles, then slowly brought up while breathing oxygen. Serious cases usually run on **US Navy Treatment Table 6**.
- **Recovery** is good for most when treatment is prompt, but not guaranteed. Some divers need several chamber sessions, and a minority are left with residual numbness, weakness, or fatigue. Speed of recompression is the biggest lever on the outcome.

## Who's most at risk

Some risk is in your hands and some isn't. The controllable factors dominate:

- **Profile and ascent:** fast ascents and missed stops are the biggest, most preventable causes. Deep, long, and repetitive multi-day dives stack gas load.
- **Body and conditions:** cold and hard exertion (especially on the bottom or during ascent), dehydration, and poor fitness all raise risk.
- **Fixed factors:** a right-to-left shunt such as a [PFO](https://donarundas.com/depth-notes/safety/predisposing-factors-for-decompression-sickness) and older age. Sex may play a part too: some recent data report higher adjusted odds for women, but the evidence is mixed and confounded, so treat it as unsettled.
- **After the dive:** flying or driving to altitude too soon.

The full breakdown is in [predisposing factors for DCS](https://donarundas.com/depth-notes/safety/predisposing-factors-for-decompression-sickness) and [fit to dive](https://donarundas.com/depth-notes/safety/fit-to-dive).

## How divers lower the risk

You can't reduce the risk to zero, only stack the odds in your favour:

- Ascend slowly and **do your safety and decompression stops**. [Safe ascents](https://donarundas.com/depth-notes/decompression/safe-ascents) covers flying the stop.
- Use conservative [gradient factors](https://donarundas.com/depth-notes/decompression/gradient-factors), and watch GF99 and Surface GF on the way up.
- Hydrate, stay warm, and skip the hard workout right after a dive.
- Leave generous surface intervals, and respect [no-fly times](https://donarundas.com/depth-notes/safety/flying-after-diving): at least 12 hours after a single no-stop dive, 18 hours after repetitive or multi-day diving, and substantially longer after decompression dives.
- Build aerobic fitness and dive sensible profiles, not aggressive ones.

## How common, and how serious

DCS is rare in recreational diving, on the order of a few cases per 10,000 dives, and most treated cases recover fully. It's also rarely what *kills* divers: the heart and running out of gas cause far more deaths, which is the subject of [what actually kills divers](https://donarundas.com/depth-notes/safety/diver-risk-physiology). The DCS risk that matters most is real Type II hitting the spinal cord, brain, inner ear, or cardiopulmonary system, which can leave lasting injury or, rarely, be fatal. What decides the outcome, more than anything, is how fast it's recognised and recompressed, which is why prompt oxygen and a call for help beat waiting it out.

> **The one-line version**
>
> DCS is dissolved gas fizzing out as bubbles when you ascend too fast. Type I is achy joints and skin; Type II is neurological and an emergency. Prevent it with slow ascents, stops, conservatism, and fitness; treat it with oxygen and recompression, fast.

---

Reading your computer, planning conservative ascents, and knowing the warning signs are core skills, not trivia. Our [technical and CCR training](https://donarundas.com/courses) builds them properly. [Get in touch](https://donarundas.com/contact) and tell us where you're at.

## References

1. Vann RD, Butler FK, Mitchell SJ, Moon RE. *Decompression illness.* Lancet. 2011;377(9760):153–164.
2. Divers Alert Network (DAN). *Decompression Sickness*, oxygen first aid, and flying-after-diving guidance.
3. Pollock NW, Buteau D. *Updates in Decompression Illness.* Emerg Med Clin North Am. 2017.
4. Moon RE (ed). *Adjunctive and supportive treatment of decompression illness* / UHMS guidance.
5. Bühlmann AA. *Decompression–Decompression Sickness.* Berlin: Springer-Verlag, 1984.

## Common questions

### What causes decompression sickness?

Dissolved inert gas (mostly nitrogen) coming out of solution as bubbles when you ascend faster than your tissues can off-gas. At depth you absorb gas under pressure; if the pressure drops too quickly on the way up, that gas forms bubbles in blood and tissue that cause mechanical and inflammatory damage. Fast ascents, missed stops, long or deep dives, repetitive diving, cold and exertion all raise the odds.

### What are the symptoms of decompression sickness?

Most often joint or limb pain (the classic 'bends'), unusual fatigue, and skin itching or a blotchy rash for milder Type I. Type II is neurological or cardiopulmonary: tingling, numbness, weakness, difficulty walking, dizziness or vertigo, visual or hearing changes, confusion, or breathing difficulty. Symptoms usually start within minutes to hours, and the large majority within 24 hours of surfacing.

### Can decompression sickness kill you?

Yes, though it is uncommon. Severe Type II DCS affecting the spinal cord, brain, inner ear, or heart and lungs can cause permanent injury or, rarely, death. The outlook is good when it is recognised early and treated promptly with oxygen and recompression, which is why fast action matters more than waiting to 'see if it passes'.

### How do you prevent decompression sickness?

Ascend slowly, do your safety and decompression stops, and use conservative computer settings. Hydrate, stay warm, avoid hard exertion right after a dive, leave adequate surface intervals, and wait before flying. General fitness and sensible, non-aggressive profiles do the rest. No method removes the risk entirely; it only lowers it.

### What is decompression sickness also known as?

The bends, caisson disease, or divers' disease. 'DCS' is the medical abbreviation. Together with arterial gas embolism it falls under the wider umbrella of decompression illness (DCI).

### How soon do decompression sickness symptoms appear?

Usually within a few hours of surfacing. About half of cases show within an hour and the large majority within 24 hours. Symptoms that appear or worsen after a dive, especially anything neurological, should be treated as possible DCS until proven otherwise.

### How is decompression sickness treated?

First aid is 100% oxygen, lying the diver flat, fluids if they can drink, and an urgent call to a diving emergency line. The definitive treatment is recompression in a hyperbaric chamber, usually on US Navy Treatment Table 6, which shrinks the bubbles and floods the tissues with oxygen. Some divers need more than one treatment, and the sooner it starts the better the recovery.

### How long should you wait to fly after diving?

Standard guidance is a minimum of 12 hours after a single no-stop dive and 18 hours after repetitive or multi-day diving. After decompression dives the recommended wait is substantially longer than 18 hours, with no firm upper limit agreed, so err well on the safe side. Flying drops the cabin pressure below sea level, which can pull lingering dissolved gas out as bubbles.

### What is the difference between decompression sickness and arterial gas embolism?

Both are decompression illness, but the mechanism differs. DCS is dissolved gas bubbling out of tissues, usually minutes to hours after a dive. Arterial gas embolism is gas forced from a burst lung straight into the arteries, with stroke-like signs within minutes of surfacing, often after a breath-hold ascent. First aid (oxygen, then recompression) overlaps, which is why both are treated urgently.

---

**Source:** [https://donarundas.com/depth-notes/safety/decompression-sickness](https://donarundas.com/depth-notes/safety/decompression-sickness)

**About the author:** Donarun Das is a TDI Trimix and KISS Sidewinder CCR instructor teaching technical and rebreather diving in the Maldives, Sri Lanka, and India. He holds the deepest verified civilian dive in India (103 m, open-circuit trimix, Lakshadweep, March 2026). Courses: https://donarundas.com/courses — enquiries: https://donarundas.com/contact

> Dive theory published by a working instructor for education. It is not medical advice and not a substitute for training. Decompression, gas, and depth decisions belong with your own training, your dive computer, and a dive medical officer.

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