Oxygen Toxicity in Diving and Hyperbaric Medicine

By Rubicon Foundation editorial team

5 min read · 1 November 2026

Oxygen toxicity is injury caused by breathing oxygen at a pressure or for a duration that exceeds the body’s tolerance. In diving and hyperbaric medicine, pressure changes how much oxygen reaches tissues, so managing exposure is central to preventing neurological emergencies and lung injury.

Why does pressure make oxygen toxic?

Oxygen is essential to cellular metabolism, but excess oxygen can generate reactive molecules that damage proteins, membranes and other cell structures. The risk depends not simply on the oxygen percentage in a breathing mix, but on its partial pressure: the portion of total gas pressure contributed by oxygen.

As a diver descends, ambient pressure rises. A gas mixture that is acceptable at the surface can therefore deliver a much higher oxygen partial pressure at depth. The same principle applies in a hyperbaric chamber, where oxygen is administered in a pressurised environment for clinical treatment.

What forms of oxygen toxicity matter underwater?

Central nervous system oxygen toxicity is the immediate concern in many diving situations. It can involve visual or auditory changes, nausea, twitching, dizziness, confusion or convulsions. A seizure underwater can cause loss of the regulator, aspiration or drowning, which makes recognition and exposure control especially important.

Pulmonary oxygen toxicity is associated more with prolonged exposure. It can irritate and inflame the airways, producing symptoms such as chest discomfort, cough or reduced breathing capacity. The likelihood and severity depend on the pressure and duration of exposure, and on the pattern of repeated oxygen breathing.

These forms are related to excess oxygen but are not interchangeable. A short, high-pressure exposure raises different concerns from a long treatment or repeated breathing of oxygen-rich gas; clinical assessment must account for the exposure history and symptoms.

How do divers manage oxygen exposure?

Dive planning treats oxygen partial pressure and exposure time as linked limits. Divers using nitrox or other oxygen-enriched mixtures must consider the maximum depth for the chosen mix, while technical and scientific divers may need to track exposures across several gases and repeated dives.

Oxygen partial pressure: determined by the oxygen fraction and the surrounding pressure.
Maximum operating depth: the depth at which a breathing mix reaches the planned oxygen partial pressure limit.
Exposure duration: relevant to both acute central nervous system risk and cumulative pulmonary stress.
Gas switching and dive profile: changes in depth and breathing mix alter oxygen exposure throughout a dive.
Individual conditions: exertion, carbon dioxide retention, immersion and other factors can affect risk.

Limits are planning tools, not guarantees that toxicity cannot occur. A diver should follow the procedures and exposure limits applicable to the gas, equipment and training being used, and avoid treating a planned limit as a target to approach casually.

Why is oxygen toxicity studied in hyperbaric care?

Hyperbaric oxygen therapy uses oxygen under pressure for medical purposes. Its clinical value depends on delivering oxygen in a controlled way, while accounting for neurological and pulmonary risks. Treatment protocols therefore consider pressure, session duration, intervals and the patient’s condition.

Research on oxygen toxicity examines how pressure and exposure shape biological injury, how risks vary among individuals, and how treatment or dive procedures can preserve benefit while limiting harm. These questions connect diving physiology with respiratory medicine, neuroscience and clinical hyperbaric practice.

If symptoms suggest oxygen toxicity during a dive or after hyperbaric treatment, the situation needs prompt professional assessment. Decisions about return to diving or further treatment belong with a physician experienced in diving or hyperbaric medicine.

What should you remember about symptoms and prevention?

Central nervous system symptoms can develop suddenly, and a seizure may leave little time for a diver to respond. Prevention relies on conservative exposure planning, correct gas identification and depth control, and attention to changes in how the diver feels and functions.

There is no single symptom pattern that confirms oxygen toxicity, and some warning signs overlap with other dive-related problems. A suspected event should be treated seriously; the dive profile, breathing gas and timing of symptoms are useful details for medical evaluation.

Frequently asked questions

Can oxygen be toxic even though divers need it to breathe?

Yes. Oxygen is necessary for life, but breathing it at sufficiently high partial pressure or for too long can injure the nervous system or lungs.

Does oxygen toxicity only affect divers using enriched gas?

No. Any breathing gas can deliver a high oxygen partial pressure when ambient pressure is high enough. Enriched mixtures require particular depth planning because their oxygen fraction is higher.

What should happen after suspected oxygen toxicity?

A suspected event warrants prompt medical assessment, especially after a seizure, breathing difficulty or persistent neurological symptoms. Consult a physician experienced in diving or hyperbaric medicine before returning to diving or treatment.

An original research-library explainer written by the Rubicon editors. It is not a summary of a specific publication.