Oxygen Toxicity in Diving and Hyperbaric Medicine

By Rubicon Foundation editorial team

5 min read · 1 November 2026

Oxygen toxicity is harmful injury caused by breathing oxygen at a partial pressure or for a duration that the body cannot safely tolerate. It matters in diving and hyperbaric medicine because increased pressure raises oxygen’s partial pressure, making exposure a central consideration in gas planning, treatment and clinical monitoring.

Why can oxygen become toxic underwater?

Oxygen is essential to metabolism, but its effects depend on partial pressure: the pressure contributed by oxygen in a breathing mixture. As ambient pressure rises underwater, the oxygen partial pressure rises too, even if the mixture itself has not changed. A gas suitable at the surface can therefore become hazardous at depth.

Risk also depends on how long exposure lasts and on the circumstances of breathing. Diving and hyperbaric care use oxygen for valid physiological and therapeutic reasons, but those benefits must be balanced against exposure. The relevant question is not simply whether a diver is breathing oxygen, but at what partial pressure and for how long.

What forms can oxygen toxicity take?

Two broad patterns are important: effects on the central nervous system and effects on the lungs. Central nervous system oxygen toxicity can develop during exposure to elevated oxygen partial pressure and may include visual or auditory changes, nausea, twitching, dizziness or convulsions. A convulsion underwater can be especially dangerous because it may compromise a diver’s ability to keep a regulator in place and maintain control.

Pulmonary oxygen toxicity is associated with prolonged exposure. It can irritate and injure the airways and lung tissue, with symptoms such as chest discomfort, coughing or breathing difficulty. These patterns differ in their typical setting and course; neither should be treated as a predictable response that occurs at the same exposure for everyone.

Partial pressure: oxygen’s share of the total breathing-gas pressure.
Exposure duration: the time spent breathing a given oxygen partial pressure.
Central nervous system effects: acute neurological symptoms, including the possibility of convulsion.
Pulmonary effects: lung irritation or injury associated with sustained exposure.

How does this shape diving practice?

Gas choice and depth determine oxygen partial pressure, while dive duration contributes to cumulative exposure. These factors are considered together when planning a dive, including when oxygen-enriched breathing mixtures are used. A plan must account for the maximum depth as well as the time spent at depth, rather than treating a gas mixture as safe under every condition.

Water adds practical consequences to neurological symptoms. A diver who becomes confused or convulses may be unable to respond effectively, and an incident can create an immediate drowning risk. Training, team procedures, equipment configuration and adherence to the dive plan are therefore part of managing oxygen exposure, not substitutes for understanding its physiological limits.

Why is oxygen toxicity also a hyperbaric concern?

Hyperbaric treatment uses oxygen under increased pressure for clinical purposes. That setting makes oxygen exposure a therapeutic variable: clinicians must consider the intended benefit alongside the possibility of neurological or pulmonary effects. Treatment conditions, duration and a patient’s medical circumstances all matter.

Oxygen toxicity sits within a wider field of pressure-related medicine. It is distinct from nitrogen narcosis and decompression sickness, although these concerns can overlap in diving operations and clinical decision-making. A diving-medicine physician or hyperbaric clinician can assess symptoms and exposure in context; suspected serious toxicity requires prompt professional evaluation.

What should readers keep in mind?

Oxygen toxicity is not a single symptom or a simple threshold that applies identically to every dive. Pressure, exposure time, breathing mixture and individual circumstances all influence risk. A diver should follow the limits and procedures established for the planned gas and dive rather than extrapolating from a different exposure.

For clinicians and researchers, the subject links respiratory physiology, neurological risk, gas management and treatment design. Studies of oxygen exposure examine how these factors interact and how benefits can be pursued while limiting harm. Questions about a particular dive, symptom or hyperbaric treatment belong with a qualified diving-medicine or hyperbaric physician.

Frequently asked questions

Does oxygen toxicity happen only at great depth?

No. Depth raises oxygen partial pressure when a diver breathes underwater, but prolonged exposure to elevated oxygen can also matter in hyperbaric treatment. The gas, pressure and exposure duration all contribute.

Are neurological and pulmonary oxygen toxicity the same?

They are different patterns of injury. Neurological effects can be acute, while pulmonary effects are associated with prolonged exposure; symptoms and circumstances vary.

What should I do if oxygen toxicity is suspected?

Treat possible serious symptoms as urgent, especially neurological symptoms during a dive. Follow established emergency procedures and seek assessment from an appropriately qualified diving-medicine or hyperbaric physician.

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