Decompression sickness and barotrauma, as DAN describes them.

Decompression illness: one name for two conditions

DAN's health resource on decompression illness, written by Ed Thalmann, MD, uses decompression illness (DCI) as an umbrella term for two conditions linked to a fall in surrounding pressure: decompression sickness (DCS) and arterial gas embolism (AGE).

Decompression sickness

What DAN says happens

DAN describes decompression sickness, often called the bends, as bubbles forming in the body's tissues and damaging them locally. It happens when pressure drops too fast for the nitrogen or other inert gas dissolved in the body during a dive to leave in an orderly way.

DAN's Dive Medical Reference fills in the mechanism. Tissues take up inert gas while under pressure. After surfacing, most tissues hold more dissolved gas than the surrounding pressure would normally allow, a state called supersaturation. When that supersaturation is large enough, bubbles can form, and the larger it is, the more likely symptoms become. The same reference makes two points worth knowing:

• Bubbles detected in the bloodstream do not on their own mean a person has DCS.
• Dive tables and dive computers are models. DAN says they cannot capture every factor that affects how the body takes up and releases gas, and cautions against relying on them too heavily.

DAN also states plainly that DCS can happen even when accepted guidelines were followed. Bird's 2013 Alert Diver article for DAN described it as rarely fatal among recreational divers, but it is still a medical condition that needs a doctor.

Risk factors DAN names

DAN adds that why some people are more susceptible than others is not fully understood. BSAC's 2024 incident report, as Divernet summarised it on 2 November 2025, found decompression illness cases still falling, with repeat diving the growing factor among the cases it did record.

Symptoms DAN lists

DAN lists a wide range: tiredness, itchy skin, pain in joints or muscles, dizziness, ringing in the ears, numbness or tingling, shortness of breath, a blotchy rash, weakness, difficulty passing urine, confusion, tremors and unconsciousness. DAN says symptoms usually appear between 15 minutes and 12 hours after surfacing. Severe cases can start before or immediately after surfacing. Late onset is rare but possible, and DAN singles out flying after diving as a situation where it can happen; see flying after diving.

Arterial gas embolism

DAN describes AGE as gas getting into the arteries, usually after expanding air injures lung tissue during ascent. DAN calls it the more serious form of decompression illness and notes it can occur even after a normal ascent. Symptoms DAN names include dizziness, blurred vision, chest pain, disorientation, paralysis or weakness, convulsions and unconsciousness. A diver with AGE may reach the surface unconscious or lose consciousness within about 10 minutes, and DAN states that AGE can be fatal.

How lung over-expansion fits into the accident data

Bird's 2013 article traces a chain of events: running out of gas, getting trapped or having an equipment problem leads to a rapid ascent; the rapid ascent over-expands the lungs; the lung injury lets gas into the arteries; and the embolism often causes unconsciousness in the water and drowning. Bird stressed that AGE, not DCS, is the condition far more likely to end in drowning. The 2008 study by Denoble and colleagues found arterial gas embolism in 29 percent of disabling injuries and 14 percent of recorded causes of death among 947 recreational scuba deaths from 1992 to 2003. For the full breakdown, see what the accident data shows.

Ear and sinus barotrauma

DAN states that middle-ear barotrauma, often called ear squeeze, is the most common injury in diving.

DAN describes it as damage from pressure that has not been equalised in the middle ear because the Eustachian tube is blocked. It is most likely during a fast descent. The result can be swelling, fluid, bleeding and a ruptured eardrum. DAN names colds, allergies and poor equalisation technique as contributors. This page does not describe how divers equalise.

DAN advises professional medical evaluation for suspected ear barotrauma, and notes that any doctor can help, not only a diving medicine specialist. It also says that vertigo, involuntary eye movements or hearing loss may point to barotrauma of the inner ear, and that further diving should be strongly discouraged until a specialist has cleared the diver.

Where medical care is found

DAN says suspected decompression illness is treated in a hyperbaric, or recompression, chamber. It also warns, in a page dated 2 September 2020, that some divers have driven past medical facilities to reach a chamber on the assumption that a chamber is the answer to any diving injury. DAN's stated position is that a diver with a suspected diving injury needs medical evaluation at a hospital or emergency clinic, and that the best choice is always the best medical service available locally. Doctors decide on treatment. For how chambers are organised and why DAN does not publish their availability, see dive insurance and chambers.

The physics behind pressure, gas volume and dissolved gas is introduced in dive physics explained. Other conditions, including immersion pulmonary oedema, nitrogen narcosis and oxygen toxicity, are on other diving illnesses.