Oxygen Toxicity in Diving and Hyperbaric Medicine

By Rubicon Foundation editorial team

5 min read · 1 November 2026

Oxygen toxicity is tissue injury caused by excessive exposure to oxygen, a risk that matters whenever divers breathe gas at elevated partial pressures. It can affect the central nervous system or the lungs, with the type and likelihood of injury shaped by oxygen pressure, exposure time and individual circumstances.

How can oxygen become toxic underwater?

Oxygen is essential for metabolism, but breathing it at a higher partial pressure increases the formation of reactive oxygen species. The body’s antioxidant systems normally limit damage; when exposure overwhelms those defences, cellular structures can be injured.

Underwater, oxygen partial pressure rises with ambient pressure and with the proportion of oxygen in the breathing gas. A gas that is appropriate near the surface may therefore become hazardous at depth. The relevant exposure is not simply the percentage printed on a cylinder: depth and duration matter too.

What are the main forms of oxygen toxicity?

Central nervous system oxygen toxicity is the acute concern during dives using oxygen-rich gas. It can cause neurological symptoms, including visual or auditory disturbance, nausea, twitching and convulsions. A seizure underwater can lead to loss of the regulator, aspiration or drowning, so the consequences may be severe even if the episode itself passes.

Pulmonary oxygen toxicity is associated with prolonged exposure. It can irritate and inflame the respiratory tract, producing symptoms such as chest discomfort, cough and reduced tolerance for exertion. The two forms involve different patterns of exposure and injury; a diver should not assume that avoiding one removes the other.

Partial pressure: the pressure contributed by oxygen in a breathing mixture; it increases as ambient pressure rises.
Exposure time: the duration of breathing oxygen at a given partial pressure, relevant to cumulative effects.
Central nervous system effects: acute neurological disturbance that can impair a diver underwater.
Pulmonary effects: respiratory irritation and injury associated with sustained oxygen exposure.
Individual variability: susceptibility can differ, and circumstances such as exertion, carbon dioxide retention and immersion may affect risk.

Why does oxygen exposure planning matter?

Divers use oxygen-rich mixtures for specific purposes, including decompression and technical diving. These gases can support a dive plan, but their safe use depends on controlling the depth at which they are breathed and the time spent at that exposure. Gas selection and the planned profile must be considered together.

Oxygen toxicity is also relevant to hyperbaric medicine, where oxygen may be administered under pressure for clinical treatment. In that setting, exposure is managed as part of a treatment protocol, with attention to pressure, duration and patient monitoring. The clinical context differs from diving, but the underlying issue is the same: oxygen dose changes with pressure and time.

How is the risk managed in diving?

Operational controls include calculating oxygen partial pressure for the planned depth, respecting the limits of the dive plan, and tracking cumulative exposure where relevant. Divers using nitrox or other oxygen-enriched gases need to analyse and label the mixture correctly and verify that the gas is appropriate for the planned maximum depth.

Recognising symptoms matters, but prevention is central because a central nervous system event can arrive without a reliable warning period. If a diver has symptoms that may indicate oxygen toxicity, the response depends on the situation and training; suspected episodes or ongoing respiratory symptoms warrant assessment by a diving-medicine physician.

What does oxygen toxicity research examine?

Research in diving and hyperbaric medicine examines how pressure, oxygen concentration, exposure duration and physiological conditions interact. It also considers how oxygen-related effects differ among tissues and how operational controls can reduce the risk without losing the intended benefit of oxygen use.

This work sits alongside broader research into decompression, breathing-gas physiology and hyperbaric treatment. Oxygen is both a therapeutic tool and a potential hazard, so the central question is not whether it is safe or unsafe in isolation, but how exposure is controlled in a particular environment and for a particular purpose.

Frequently asked questions

Does oxygen toxicity only affect technical divers?

No. The risk depends on oxygen partial pressure and exposure, not on a diver’s label. It is relevant whenever a breathing gas or hyperbaric environment produces a substantial oxygen exposure.

Can a diver predict a central nervous system event from symptoms?

Symptoms may occur, but they are not a dependable advance warning. Dive planning and exposure control are essential; a suspected episode should be discussed with a diving-medicine physician.

Is oxygen toxicity the same as decompression sickness?

No. Oxygen toxicity results from excessive oxygen exposure, while decompression sickness involves inert gas coming out of solution during or after pressure reduction. Both matter in dive planning, but they are distinct problems.

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