Oxygen & Hyperbaric - Chambers & safety
The real risks of hyperbaric environments
Last updated 30 September 2026. How we write this .
Most hyperbaric problems are brief ear pressure pain. Oxygen seizures, eyesight changes and fire are rarer but real, and the risk grows when a chamber runs outside medical oversight.
Start here Most hyperbaric problems are brief ear pressure pain. Oxygen seizures, eyesight changes and fire are rarer but real, and the risk grows when a chamber runs outside medical oversight.
By the end, you will understand How often does something go wrong? How likely is an oxygen seizure? Can hyperbaric oxygen change your eyesight? Key words used in this lesson Hyperbaric Above normal atmospheric pressure. Hyperbaric oxygen therapy involves breathing oxygen in a pressurised chamber, which increases the amount dissolved in the blood. Full plain-English glossary
Where this information comes from Claim-cited evidence. Central research claims on this lesson are linked to specific studies or official guidance.
This lesson links the specific studies and guidance used for its central claims.
The safety of hyperbaric oxygen treatment: retrospective analysis in 2,334 patients - Undersea and Hyperbaric Medicine, 2016Seizures during hyperbaric oxygen therapy: retrospective analysis of 62,614 treatment sessions - Undersea and Hyperbaric Medicine, 2016Complications and side effects of hyperbaric oxygen therapy - Aviation, Space, and Environmental Medicine, 2000Myopic shift and lens turbidity following hyperbaric oxygen therapy: a prospective, longitudinal, observational cohort study - Acta Ophthalmologica, 2019Our standard: expert or athlete opinion may illustrate a viewpoint, but it is never treated as proof. Read the editorial policy .
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The commonest harm from a hyperbaric chamber is ear pain as the pressure rises, and most of it settles quickly. The serious risks are rarer: a seizure caused by oxygen, changes to eyesight over a long course, and fire. How likely each one is depends heavily on who runs the chamber, how people are screened, and how many sessions they have.
How often does something go wrong?
One of the largest safety audits comes from the Sagol Center for hyperbaric medicine in Israel. Hadanny and colleagues looked back at 2,334 patients who had 62,614 sessions between 2010 and 2014. Just over one patient in six, 17.4%, had at least one adverse event during their course. Counted per session, the rate was 0.72%, or about seven events in every 1,000 sessions.
Ear injury from pressure, called barotrauma, was the main problem. It affected 9.2% of patients but only 0.04% of sessions. Women and children under 16 were more likely to get it. Low blood sugar, oxygen toxicity, dizziness, anxiety, breathlessness and chest pain each affected between 0.5% and 1.5% of patients.
Those two ways of counting answer different questions. A per-session figure tells a unit how often its staff will deal with a problem. A per-patient figure tells you what to expect across a whole course of treatment, and it is always the bigger number. When a clinic quotes a safety figure, it is worth asking which one it is.
Definitions matter too. A German unit led by Plafki tracked 782 patients through 11,376 sessions. More than 17% reported ear pain or discomfort, but only 3.8% had an injury that a doctor could actually see when examining the ear under a microscope.
How likely is an oxygen seizure?
Breathing pure oxygen at high pressure can over-excite the brain and trigger a seizure. Doctors call this central nervous system oxygen toxicity. Earlier reports put the risk anywhere between 1 in 10,000 and 1 in 600 sessions, which is a very wide range.
The Israeli audit tightened that estimate. Seizures happened in 1 of every 8,945 sessions, in seven patients in total, and only one was clearly caused by oxygen: 1 in 62,614 sessions. The authors found no extra seizure risk in people treated for long-term neurological conditions, with one exception, uncontrolled epilepsy. In the German series, four patients had seizures with no warning signs and no obvious risk factors. None had a repeat, and none had lasting effects.
A 2017 review of HBOT side effects by Marvin Heyboer and colleagues at SUNY Upstate Medical University reached the same view. A single oxygen seizure leaves no known lasting damage, and people who have one can often go on to finish their treatment.
Can hyperbaric oxygen change your eyesight?
Yes, and more often than most people expect. Repeated sessions tend to make the lens of the eye bend light more strongly, so distant objects blur. This is called a myopic, or short-sighted, shift. Eye changes are measured in dioptres, the same unit used for glasses prescriptions.
At Sahlgrenska University Hospital in Sweden, Riedl's team examined 29 patients before, during and after a course of 40 standard treatments. A shift of at least half a dioptre towards short-sightedness appeared in 45 of the 58 eyes, 77.6%. By a 12-week follow-up, eyesight had mostly returned to where it started, though a small change persisted in left eyes. The lens centre also became slightly more coloured and cloudy, and the authors concluded that reduced lens clarity is a potential consequence of treatment.
Very long courses carry a bigger risk. In 1984 Swedish researchers reported on 25 patients who had 150 or more exposures. All of them became more short-sighted. Of the 15 whose lens centres were clear at the start, 7 developed a nuclear cataract, a clouding in the middle of the lens, and lost some sharpness of vision. Heyboer's review notes that new cataracts are rare in US practice because courses there rarely exceed 75 treatments. That is worth keeping in mind for any course with no defined end.
Why is fire the worst-case risk?
Oxygen does not burn, but it makes everything around it burn far more easily and fiercely. In a 1997 analysis, Sheffield and Desautels counted 77 deaths in 35 hyperbaric chamber fires between 1923 and 1996. Every fatal fire happened in air enriched with oxygen, above 28%, with plenty of burnable material inside. The only survivors were in chambers filled with ordinary air. Before 1980 most fires started from electrical faults. After 1980, most started from banned items that the person inside had carried in.
Fires still happen. On 31 January 2025, a five-year-old boy died in a chamber fire at a clinic in Troy, Michigan. The state's Attorney General said a single spark started the fire and he died within seconds. According to his family's lawyer, he was being treated for sleep apnoea and ADHD, neither of which is an FDA-approved use. NBC News also recalled a 2009 fire at an unaccredited Florida clinic that killed a four-year-old boy and his grandmother.
Does it matter where the chamber is?
A great deal. NBC reported that nearly 150 facilities in the US were accredited by the Undersea and Hyperbaric Medical Society, while the society's executive director estimated that thousands of spas and wellness businesses run chambers without accreditation. Michigan, like other US states, had no law covering how chambers are operated or maintained outside hospitals.
Lower pressure does not make a chamber risk free. A 2026 review in the journal Undersea and Hyperbaric Medicine looked at soft-sided and so-called mild hard-sided chambers, which typically run at 3 to 5 psi above normal air pressure, roughly a fifth to a third extra. Many fail to meet FDA clearance, US fire codes or pressure-vessel safety standards. The review lists ear and lung barotrauma, suffocation, fire, structural failure and, in extreme cases, death among the reported harms.
In England, the Care Quality Commission regulates hyperbaric oxygen therapy when a health professional provides or supervises it as treatment for a disease, disorder or injury. A registered provider must be able to show the treatment is safe, effective and appropriate. A session sold purely as wellness, with no health professional involved, may fall outside that system.
This is also where the real uncertainty lies. Almost every number in this lesson comes from hospital units that screen patients, monitor every session and keep records. Nobody publishes comparable adverse event data from spas and wellness studios, so their true risk is simply unknown.
If someone has a seizure, chest pain or sudden breathlessness during or after a session, call 999. For ear pain that does not settle, a change in hearing or blurred vision, speak to your GP or call NHS 111.
This lesson is general education about hyperbaric safety, not medical advice. Decisions about hyperbaric treatment belong with an NHS or specialist hyperbaric doctor.
Related in this classroom The studies behind this page The safety of hyperbaric oxygen treatment: retrospective analysis in 2,334 patients - Undersea and Hyperbaric Medicine, 2016Seizures during hyperbaric oxygen therapy: retrospective analysis of 62,614 treatment sessions - Undersea and Hyperbaric Medicine, 2016Complications and side effects of hyperbaric oxygen therapy - Aviation, Space, and Environmental Medicine, 2000Myopic shift and lens turbidity following hyperbaric oxygen therapy: a prospective, longitudinal, observational cohort study - Acta Ophthalmologica, 2019Nuclear cataract and myopia during hyperbaric oxygen therapy - British Journal of Ophthalmology, 1984Hyperbaric and hypobaric chamber fires: a 73-year analysis - Undersea and Hyperbaric Medicine, 1997A critical look at soft-sided and hard-sided mild hyperbaric chambers: risks, regulations, and ethical oversights - Undersea and Hyperbaric Medicine, 2026Michigan boy's death raises concerns about unregulated hyperbaric oxygen therapy outside of health care facilities - NBC News, 2025Sources for this classroom
Educational content only. Not medical advice, diagnosis or treatment. Always consult a qualified healthcare professional before changing your health regimen.