Other diving illnesses, named and described by the medical bodies.

Immersion pulmonary oedema

DAN's Dive Medical Reference, in the chapter of The Heart and Diving on pulmonary and venous disorders, describes immersion pulmonary oedema (IPE, also written IPO) as fluid collecting in the tissue of the lungs in divers and swimmers. DAN links it to being immersed upright, which shifts blood into the chest and raises the pressure in the lungs' small blood vessels.

DAN lists the contributing factors as denser breathing gas, cold water, exertion or panic, and drinking too much fluid. It says the risk rises with age, obesity and high blood pressure, but that most people who have had IPE showed no obvious susceptibility. DAN states that a repeat episode is likely after a first one, and that anyone who has had IPE should have a detailed medical work-up and discuss whether to keep diving with a physician.

BSAC's Diving Incident Report for 2024, posted 12 November 2025, recorded seven medically confirmed IPE cases and one possible case, none of them fatal. BSAC credited better training with earlier recognition and stressed getting medical advice to rule out IPE before diving again.

Patent foramen ovale

DAN describes a patent foramen ovale (PFO) as a hole in the wall that separates the two upper chambers of the heart, the atria. DDRC Healthcare of Plymouth, UK, says on an undated page that about 20 to 25 percent of people, roughly one in four, have one, and that it usually causes no trouble in everyday life.

DDRC says divers who think they may have a PFO should see a cardiologist with an interest in diving. Because PFO is linked with migraine with aura, DDRC also says people who have migraine should talk to a diving doctor before diving.

Two diving medicine bodies have published joint position statements on the subject. The South Pacific Underwater Medicine Society (SPUMS) and the UK Sport Diving Medical Committee (UKSDMC) published one in 2015 in Diving and Hyperbaric Medicine (volume 45, issue 2). SPUMS and the UK Diving Medical Committee, the same committee under its current name, published an update in March 2025 (volume 55, issue 1) covering atrial shunts including PFO. We could not read the text of either statement, so their conclusions are not given here.

Nitrogen narcosis

DAN's Alert Diver article Breathing Gases, by Georgia Hausserman (1 May 2017), says nitrogen's narcotic effect typically begins at around 24 to 30 metres (80 to 100 feet) when breathing air or nitrox. It notes that people differ, and that the same diver can react differently from one dive to the next.

A DAN Alert Diver case article, Know the Risks (Yue, Li, Abraham and Scott, 18 July 2021), describes narcosis as feeling intoxicated, with poor judgment, trouble concentrating and swings of mood from euphoria to fear. The authors say fatigue, depth, alcohol and cold may make it more likely, and that impaired judgment underwater can have deadly consequences.

Oxygen toxicity and helium

The same 2017 DAN article says that breathing oxygen at high partial pressure can cause central nervous system oxygen toxicity, with seizures that may lead to drowning. DAN states this can happen at recreational depths and without warning, and that the risk rises with exposure time, exertion and some medicines. DAN lists a 2017 study by Buzzacott and Denoble on possible oxygen toxicity seizures among its fatality research.

DAN adds that helium does not cause narcosis, which is why it is used in mixtures for deeper dives, but that very deep helium dives can cause a separate condition, high-pressure nervous syndrome. Gas mixtures are a matter for specialist training; see specialty certifications.

Carbon dioxide and carbon monoxide

In The Physiology of Compressed-Gas Diving (Alert Diver, 1 August 2016), Simon Mitchell, PhD, explains that divers are prone to retaining carbon dioxide. He names the work of breathing, a reduced drive to breathe, skip breathing and dead space in the equipment. Effects include breathlessness, headache and unconsciousness, and raised carbon dioxide can make narcosis, oxygen toxicity and decompression illness worse.

DAN's Travelers Medical Guide describes carbon monoxide as an odourless, colourless poisonous gas produced by incomplete burning. It says carbon monoxide can get into scuba cylinders that are filled carelessly, and can also come from boat engine exhaust in poorly ventilated spaces.

Drowning and the heart

DAN's Travelers Medical Guide defines drowning as breathing impairment caused by being submerged. It names risk factors including alcohol around water, medical conditions such as epilepsy, and not knowing the local water hazards. Among causes of snorkeller deaths, the guide lists sudden cardiac arrest, immersion pulmonary oedema, blackout after long breath-holding, inhaling water, being struck by watercraft, and strong currents.

Heart problems are a major theme in DAN's data. A DAN blog post of 10 July 2020 says DAN researchers found the risk of dying while diving rises with age, mainly because of heart problems, and that heart-related death while diving is about ten times as likely in divers over 50 as in divers under 50. For more on what DAN publishes about age and heart health, see fitness to dive.

Marine stings

The 2021 Know the Risks article also describes Irukandji syndrome, caused by the sting of certain box jellyfish. Symptoms usually begin 5 to 90 minutes after the sting, and the authors state that about 3 percent of cases progress to heart failure. In the case they reviewed, they note that seeking emergency care would have been the right choice. Other marine life injuries are covered on environmental hazards.