Is Hyperbaric Oxygen Therapy Safe? Side Effects and Risks

Hyperbaric oxygen therapy (HBOT) is generally safe when it is prescribed for an accepted condition and delivered in a properly run medical facility, and serious complications are rare. The most common problem is ear pressure injury (barotrauma), which is usually minor. Temporary short-sightedness is common during long courses, oxygen-induced seizures are rare, and the only absolute contraindication is an untreated collapsed lung (pneumothorax).

Below are the side effects with the numbers published in medical reviews, the conditions that rule treatment out or need a doctor's review, and what the U.S. Food and Drug Administration (FDA) has said about fire risk and unproven claims.

Is Hyperbaric Oxygen Therapy Safe?

The FDA's consumer guidance on HBOT stated that when chambers are used for FDA-cleared indications, "HBOT is generally safe, and serious complications are rare." A 2017 review in Advances in Wound Care (Heyboer and colleagues) called it "among the safest therapies used today", while stressing that its side effects need to be understood for informed consent.

This table summarises how often the main side effects occur, based on that review and the studies it cites.

Side effect	How often it is reported	What usually happens
Middle ear barotrauma	Anywhere from about 2% to 84% of patients; 43% in one large series	84% of cases in that series were minor (the lowest two grades)
Temporary short-sightedness (myopia)	25% to 100% of patients after several weeks of treatment	Usually returns to baseline within 3 to 6 weeks, occasionally 6 to 12 months
Oxygen toxicity seizure	Traditionally about 1 in 10,000 treatments; recent studies report 3 to 6 per 10,000	Managed by switching the patient from oxygen to air; risk rises with pressure
Confinement anxiety in a one-person chamber	8 per 10,000 treatments	Sometimes managed with anti-anxiety medication
Nosebleed from sinus barotrauma	1 per 10,000 treatments	Rare
Symptomatic low blood sugar in people with diabetes	0.19% to 0.3% of treatments in two studies	Glucose monitoring allows most people with diabetes to be treated safely
Cataract	Rare; reported mainly after 150 or more treatments	Not expected in a typical course

Ear and Sinus Barotrauma

As the chamber pressurises, the air in your middle ear and sinuses is compressed (Boyle's law). If air cannot pass through the Eustachian tube to equalise, you feel pressure or pain, and in more severe cases the eardrum can bleed or tear. StatPearls describes middle ear barotrauma as the most common complication of both diving and clinical HBOT.

How to reduce it:

Equalise early and often by swallowing, yawning or gently pinching your nose and blowing.
Tell the operator straight away if your ears hurt. Operators can pause or slightly reduce the pressure until you clear your ears. The Heyboer review found a slow compression rate of 2 psi per minute was best for preventing ear injury.
Do not start a session with a cold. StatPearls lists active upper respiratory and severe sinus infections as relative contraindications because they raise the risk of sinus and ear barotrauma.
If you repeatedly cannot clear your ears, a doctor may suggest a decongestant nasal spray or small ear tubes (tympanostomy tubes).

Tooth pain caused by pressure changes (dental barotrauma) is also described, but it has mainly been measured in divers and aircrew.

Vision Changes: Temporary Short-Sightedness

Many people notice distance vision getting blurrier over a course of treatment. Heyboer's review reports myopia in 25% to 100% of patients after several weeks, progressing by roughly 0.25 dioptres per week while treatment continues. It usually reverses within 3 to 6 weeks of stopping, although it can take 6 to 12 months.

The 2023 Cochrane review of HBOT for radiation injury confirmed this with high-certainty evidence: patients receiving HBOT were about four times as likely to have reduced visual acuity, which the authors described as usually temporary. Because the change usually reverses, ask your eye doctor before buying new glasses during or just after a course.

New cataracts are rare. They have been reported mainly after 150 or more treatments, and most courses are far shorter.

Tell the team about any eye surgery. StatPearls warns that air or gas left in the eye after some eye operations is a contraindication, because pressure changes can damage the eye.

Oxygen Toxicity and Seizures

Breathing oxygen at high pressure can irritate the nervous system. Early warning signs include vision changes, ringing in the ears, nausea, twitching, irritability and dizziness, and in rare cases a seizure.

How rare? Figures vary by pressure and patient group:

Heyboer's review cites a traditional estimate of about 1 in 10,000 treatments, with more recent studies reporting between 1 in 1,651 and 1 in 3,388 treatments (roughly 3 to 6 per 10,000).
An Israeli study of 62,614 sessions in 2,334 patients (Hadanny 2016) recorded seizures in 1 of every 8,945 sessions, and only one seizure was clearly caused by oxygen toxicity. The authors concluded HBOT was safe for people with chronic neurological conditions, except uncontrolled epilepsy.

Risk factors include higher treatment pressure, carbon monoxide poisoning, low blood sugar and an overactive thyroid. The treatment for oxygen toxicity is to lower the oxygen dose, usually by switching the patient from oxygen to air.

Lung (pulmonary) oxygen toxicity develops with long continuous exposure, for example after about 3 to 6 hours at 2.0 ATA. Treatment sessions are shorter than this and include air breaks, and Heyboer's review notes that most current HBOT protocols do not cause lung symptoms.

Claustrophobia

One-person (monoplace) chambers are enclosed tubes. Confinement anxiety is reported in about 8 of every 10,000 monoplace treatments. StatPearls notes that whether claustrophobia rules out HBOT depends on how severe it is, how well it responds to anti-anxiety medication and the size of the chamber. Chamber size matters, so ask whether a multiplace chamber is available: these larger rooms hold several patients, who breathe oxygen through a mask or hood. See our guide to chamber types.

Fire Safety

Pressurised oxygen is a serious fire hazard, which is why chambers have strict rules on what goes inside.

In an August 2025 letter to health care providers, the FDA said it was aware of "recent reports of fires that occurred with HBOT devices that resulted in serious injuries and deaths". It told facilities to follow the manufacturer's instructions, enforce fire prevention measures, train staff, supervise patients for the whole session and dress them in compatible materials such as cotton.
StatPearls notes that patients must remove make-up, oils, deodorants and similar products, and that chambers are grounded to prevent static sparks.
The FDA's consumer page warned that explosions and fires have occurred in chambers not reviewed by the FDA at unaccredited facilities, and that people have turned soft zippered altitude bags into homemade oxygen chambers, creating fire and suffocation risks.

Phones and lithium batteries are a common question; our article on phones and batteries in hyperbaric chambers covers the rules.

Who Should Not Use a Hyperbaric Chamber?

StatPearls lists untreated pneumothorax as the only absolute contraindication. The gas trapped around the lung expands as pressure drops at the end of the session and can turn into a life-threatening tension pneumothorax. The same chapter suggests gas trapped in the eye should also rule out anything but life-saving treatment.

Many other conditions are relative contraindications. They do not automatically rule HBOT out, but a hyperbaric physician must weigh them first.

Area	Conditions that need review
Lungs	COPD, asthma, blebs or bullae on imaging, previous spontaneous pneumothorax, previous chest surgery
Medicines	Doxorubicin (usually stopped at least 24 hours before), disulfiram, cisplatin, mafenide, and past bleomycin treatment
Ears, nose and sinuses	Eustachian tube problems, past ear surgery, colds and sinus infections
Brain and seizures	Epilepsy, high fever (over 39 °C)
Eyes	Past eye surgery, history of optic neuritis, glaucoma, keratoconus
Implanted devices	Implanted defibrillators, epidural pain pumps and other devices need the manufacturer's pressure rating
Other	Pregnancy, insulin-treated diabetes, severe claustrophobia, recent nicotine or caffeine use, congenital spherocytosis

Two points often surprise people. Pregnancy has traditionally been a relative contraindication, yet StatPearls notes HBOT can improve outcomes for the baby in serious carbon monoxide poisoning. And active cancer is not considered a contraindication, because the available evidence suggests HBOT has little or no effect on cancer progression.

Pros and Cons of Hyperbaric Chamber Therapy

Pros

Accepted by UHMS, ECHM and Medicare for a defined list of conditions, such as decompression sickness, carbon monoxide poisoning, selected diabetic foot ulcers and radiation injuries. See our guide to accepted HBOT indications.
Non-invasive, and serious complications are rare when it is used for those conditions.

Cons

Time: UHMS notes that most conditions need daily treatments for several weeks.
Common, mostly mild side effects: ear barotrauma and temporary short-sightedness.
Many advertised uses are unproven. The FDA stated HBOT devices are not proven to cure cancer, Lyme disease, autism or Alzheimer's disease.
"Mild" hyperbaric sessions below 1.5 ATA, often offered in soft-shell chambers at wellness centres, are described by UHMS as unproven. UHMS also warns that these facilities often operate without following fire safety and chamber construction standards.

What the FDA Says About Unapproved Claims

The FDA's consumer update "Hyperbaric Oxygen Therapy: Get the Facts" (content current as of July 2021) listed 13 conditions for which chambers were cleared, including decompression sickness, carbon monoxide poisoning, radiation injury and non-healing diabetic foot ulcers. It said the FDA had not cleared HBOT devices for any other condition. It also noted that soft zippered chambers are cleared only to treat altitude sickness and are not cleared for use with oxygen tanks or concentrators.

It advised checking with your health care provider first and, if HBOT is recommended, using a facility accredited by the Undersea and Hyperbaric Medical Society (UHMS). As of September 2026 that page is no longer on fda.gov; an archived copy is linked in the sources below.

How to Lower Your Risk

Get screened by a doctor first. StatPearls recommends a thorough evaluation before treatment, especially if you have a chronic condition.
Choose an accredited medical facility with trained staff, and ask what pressure and chamber type they use. Our checklist on how to choose an HBOT clinic can help.
Bring a full medication list, including chemotherapy and disulfiram.
Reschedule if you have a cold or blocked sinuses.
Follow the clothing and item rules exactly: usually cotton clothing and no make-up, oils or deodorant.
If you have diabetes, expect blood sugar checks around your sessions.
Speak up about ear pain, twitching, vision changes or anxiety during the session.

To compare providers near you, browse hyperbaric clinics near you and check whether they treat medical conditions in hard-shell chambers.

Sources

Heyboer M 3rd, Sharma D, Santiago W, McCulloch N. Hyperbaric oxygen therapy: side effects defined and quantified. Advances in Wound Care. 2017;6(6):210-224.
Hadanny A, Meir O, Bechor Y, Fishlev G, Bergan J, Efrati S. Seizures during hyperbaric oxygen therapy: retrospective analysis of 62,614 treatment sessions. Undersea & Hyperbaric Medicine. 2016;43(1):21-28.
Gawdi R, Yrastorza J, Cooper JS. Hyperbaric oxygen therapy contraindications. StatPearls. Updated 27 May 2025.
Jones MW, Brett K, Han N, Cooper JS, Wyatt HA. Hyperbaric physics. StatPearls. Updated 31 January 2024.
Lin ZC, Bennett MH, Hawkins GC, Azzopardi CP, Feldmeier J, Smee R, Milross C. Hyperbaric oxygen therapy for late radiation tissue injury. Cochrane Database of Systematic Reviews. 2023;8(8):CD005005.
U.S. Food and Drug Administration, Follow instructions for safe use of hyperbaric oxygen therapy devices: letter to health care providers (25 August 2025)
U.S. Food and Drug Administration, Hyperbaric oxygen therapy: get the facts (consumer update, content current as of 26 July 2021; archived copy)
Thom SR. Hyperbaric oxygen: its mechanisms and efficacy. Plastic and Reconstructive Surgery. 2011;127 Suppl 1:131S-141S.
Undersea and Hyperbaric Medical Society, Indications for hyperbaric oxygen therapy

This article is for information only and is not medical advice. If you have symptoms during or after a session, tell the chamber staff or contact your doctor. In an emergency, call your local emergency number.