Hyperbaric Oxygen Therapy

Early pressure chambers

Accounts of hyperbaric medicine usually begin with Nathaniel Henshaw, an English physician of the 1660s. A 2021 review of hyperbaric oxygen in burn care repeats the common account that in 1662 he placed patients in a container pressurized with air. A 2024 historical analysis in the journal of the Undersea and Hyperbaric Medical Society disputes this, arguing from Henshaw's own treatise that his air chamber was a proposal that was never built, and that a working air chamber appeared only about 170 years later.

The same 2024 analysis notes that Henshaw proposed pressures up to three times atmospheric pressure for prolonged periods, exposures that its author judges would likely have caused fatal decompression sickness on return to normal pressure, a condition then unknown. These early chambers used compressed air. Breathing pure oxygen under pressure came later, after oxygen was described in the 1770s.

From diving medicine to hospital practice

The 2021 burn-care review dates several milestones. In 1878 the French physiologist Paul Bert described toxic effects of oxygen under pressure on the central nervous system. In 1937 Behnke and Shaw used hyperbaric oxygen for decompression sickness. In 1955 Churchill-Davidson used it alongside radiation therapy and Boerema developed it as an adjunct to cardiac surgery, and in 1965 Wada and Ikeda in Japan applied it to coal miners with carbon monoxide poisoning who also had burns.

Decompression illness, the condition most closely tied to the field's origins, affects divers, compressed-air workers, aviators and astronauts. A 2011 Lancet review describes recompression while breathing 100% oxygen as its definitive treatment. Professional societies later compiled indication lists for hospital use, and since the 2000s lower-pressure soft chambers have been sold for wellness and home use outside that framework, as recent reviews in the society's journal describe.

Clinical definition

In clinical usage the term means whole-body exposure to raised pressure while breathing close to 100% oxygen. The 2021 burn-care review defines it as breathing 100% oxygen at between 2 and 3 atmospheres absolute (ATA). The Undersea and Hyperbaric Medical Society (UHMS), a professional body, uses a narrower working definition: a physician-prescribed treatment in a hard-sided chamber built to recognized pressure-vessel and fire codes, at not less than 2.0 ATA, usually for 90 to 120 minutes.

The UHMS page adds that treatments with scientific support are usually given between 1.9 and 3.0 ATA. Breathing oxygen through a mask at ordinary pressure, or pressurizing only one limb, falls outside this definition. Clinicians also use the abbreviations HBOT, HBO and HBO2 interchangeably, and recompression for treatment of diving injuries.

Mild hyperbaric therapy

Mild hyperbaric oxygen therapy, sometimes shortened to mHBOT, usually refers to soft-sided or low-pressure chambers run at about 1.3 ATA, often with room air or modestly enriched oxygen. The UHMS describes exposures below 1.5 ATA as mild hyperbaric treatment that lacks scientific support. A 2026 narrative review describes mild treatment as using shallower depths and lower oxygen concentrations than traditional treatment, with different physiology and clinical uses.

Because sellers and some researchers use the same name for both, findings from 100% oxygen at 2 to 3 ATA cannot be assumed to apply to air at 1.3 ATA. A 2025 review of use in athletes notes that the vessels used for mild treatment are typically intended for altitude sickness. This page treats mild exposure as a separate intervention throughout.

Hospital chambers

In hospital practice a person lies or sits in a monoplace chamber, usually filled with oxygen, or sits with others in a larger multiplace chamber pressurized with air while breathing oxygen through a hood or mask. The chamber is compressed, held at treatment pressure, then slowly decompressed. UHMS describes sessions as typically 90 to 120 minutes, prescribed by a physician, and courses for wounds or radiation injury may involve dozens of sessions.

During compression, people are taught to equalize middle ear pressure, and the 2017 side-effect review reports that slower compression of about 2 psi per minute was associated with less ear injury in one study. Staff screen for conditions such as an untreated collapsed lung before treatment, and implanted devices may need individual assessment, according to a 2014 review of medical devices in chambers.

Mild and soft-sided chambers

Mild sessions typically take place in inflatable fabric or lightweight hard-shell chambers at wellness centers, sports facilities, clinics or homes. A 2026 review in the society's journal describes them as low-pressure chambers that operate at about 3 to 5 psi above ambient pressure. The UHMS indications page notes that such sessions are widely offered in wellness centers and spas outside medical facilities, often without adherence to fire safety and chamber construction standards.

Protocols in mild settings vary. The 2009 autism trial discussed below gave forty one-hour sessions at 1.3 atmospheres with 24% oxygen. The sources reviewed do not describe a common training standard for operators of mild chambers.

Listed hospital indications

The UHMS list of indications, last revised in 2020 per the page, includes air or gas embolism, carbon monoxide poisoning, gas gangrene, crush injury, decompression sickness, central retinal artery occlusion, selected problem wounds, severe anemia, intracranial abscess, necrotizing soft tissue infections, refractory osteomyelitis, delayed radiation injury, compromised grafts and flaps, acute thermal burns, sudden sensorineural hearing loss and avascular necrosis. A listing reflects the society's judgment and does not mean that each indication has strong trial evidence.

In this setting the therapy is usually an adjunct alongside surgery, wound care, antibiotics or emergency treatment, and is not offered as a stand-alone approach. The 2017 side-effect review describes diabetic foot ulcers and late radiation injury as the main wound uses in practice.

Elective and off-label uses

Outside listed indications, people seek hyperbaric sessions for autism, long COVID, sports recovery, general wellness and aging. Some of these uses are studied in hospital-grade chambers at 2 ATA or more, and others in mild chambers. Supporters of mild exposure describe improved oxygen delivery to tissues. A 2025 review notes that mild treatment has been used to aid post-exercise recovery and reduce fatigue in athletes.

Anti-aging claims draw partly on a 2020 Israeli study in adults aged 64 and older that reported longer telomeres and fewer senescent blood cells after 60 daily sessions. These are laboratory markers, not measures of health or lifespan, and the study reported no comparison group.

Established indications

For decompression illness, the 2011 Lancet review states that recompression with 100% oxygen is the definitive treatment and is in most cases effective, although serious cases can leave residual deficits even after several recompressions. This rests on clinical experience and physiology rather than placebo-controlled trials, which the review does not report.

A 2015 Cochrane review of chronic lower-limb wounds pooled five trials with 205 people with diabetic foot ulcers and found more ulcers healed at six weeks with hyperbaric oxygen (risk ratio 2.35), but the benefit was not evident at one year, and there was no significant difference in major amputation. The authors were not confident in the results because of flaws in trial design and reporting.

A 2011 Cochrane review of carbon monoxide poisoning included six trials with 1,361 participants. Two trials reported fewer neurological after-effects at one month and four did not, the pooled estimate was not statistically significant, and all trials had design or analysis flaws. The authors concluded that existing trials do not establish whether hyperbaric oxygen reduces adverse neurological outcomes.

Off-label uses in hospital chambers

A 2016 Cochrane review of autism found one eligible trial, 60 children in Thailand given 100% oxygen at 1.5 ATA or a sham. The review rated evidence low quality and found no improvement in social interaction, behavior, communication or cognition, while minor ear barotrauma was more common with treatment. The review excluded trials of 24% oxygen because they did not meet its definition of hyperbaric oxygen.

For long COVID, a 2024 BMJ living systematic review of 24 randomized trials found no compelling evidence that hyperbaric oxygen improves outcomes, alongside many other interventions in the same position. Small uncontrolled studies have reported changes in fatigue and cognition, but they do not establish effect.

Mild chambers and wellness aims

Controlled evidence for mild exposure is sparse. A 2009 multicenter trial randomized 62 children with autism to 40 sessions at 1.3 atmospheres with 24% oxygen or to slightly pressurized room air, and reported better clinician-rated global functioning in the treatment group. It was a single trial with short follow-up, it was later excluded from the Cochrane review because of its low oxygen concentration, and the sources reviewed found no confirming trial.

A 2025 review of athletes concluded there is limited evidence for hyperbaric treatment to aid recovery from musculoskeletal injury or mild brain injury. A 2026 review notes that mild treatment has not been studied extensively for wounds. Neither the Cochrane wound review nor the decompression literature applies to mild chambers, and no verified trial was found showing that mild sessions slow aging.

Ear, sinus and lung effects

Middle ear barotrauma is the most common side effect. A 2017 review reports rates from about 2% to 84% in people breathing on their own, with 43% in one large study, most cases minor and without eardrum rupture. Sinus injury with nosebleed is rare, around one per 10,000 treatments. The same review names an untreated collapsed lung (pneumothorax) as an absolute contraindication, because decompression can turn it into a life-threatening tension pneumothorax.

The 2016 autism review found more side-effect events, mainly minor ear barotrauma, in children given hyperbaric oxygen than in those given sham. Reviews of mild chambers list ear and lung barotrauma among reported harms, so lower pressure does not remove this risk.

Oxygen toxicity and eye changes

Oxygen under pressure can trigger seizures. The 2017 review cites a traditional estimate of about one per 10,000 treatments and more recent figures of about one per 2,000 to 3,000, rising with pressure, from about 3 to 5 per 10,000 at 2.0 ATA to 3 to 6 per 10,000 at 2.4 to 2.8 ATA. People with diabetes can occasionally become hypoglycemic after sessions, although the review reports that symptomatic cases were uncommon.

Temporary nearsightedness, called hyperoxic myopia, develops in 25% to 100% of people after several weeks at 2.0 ATA or more, at about 0.25 diopter per week, and usually reverses within three to six weeks. Cataract formation is linked to very long courses, usually 150 sessions or more.

Confinement and fire

Claustrophobia and confinement anxiety occur in a minority of sessions, recorded at about 8 events per 10,000 treatments in monoplace chambers in the 2017 review. Fire is the most catastrophic hazard. A 1997 analysis counted 77 deaths in 35 hyperbaric chamber fires from 1923 to 1996 across Asia, Europe and North America. Every fatal fire occurred in an oxygen-enriched atmosphere with abundant burnable material, and since 1980 most were ignited by prohibited items carried inside.

A 2014 review warns that defibrillation inside a chamber carries fire risk and that implanted devices may malfunction under pressure. Reviews published in 2026 report that both mild and traditional chambers have been linked to life-threatening events including fire, explosion and suffocation, and that adherence to safety standards varies among facilities.

Suitability and care boundaries

Suspected decompression illness or carbon monoxide poisoning is an emergency handled by medical services, and a wellness chamber is not a substitute for that care. For other conditions, the sources reviewed support discussing any planned sessions with a clinician who knows the person's medical history, lungs, ears, eyes, implanted devices and medicines, and not delaying or replacing necessary treatment.