Hyperbaric Oxygen Therapy Side Effects and Risks: What You Need to Know [2026]

Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before starting hyperbaric oxygen therapy. Individual results and risks vary based on your medical history and specific conditions.

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Hyperbaric oxygen therapy has gone from a niche wound-care treatment to one of the most talked-about therapies in wellness and recovery. Clinics are opening everywhere. Athletes swear by it. Longevity enthusiasts can't stop posting about their sessions.

But here's what most of those glowing testimonials skip: every medical treatment carries risk. And while HBOT is genuinely one of the safer interventions out there, "safe" doesn't mean "zero side effects." It means the risks are manageable — when you understand them.

This guide breaks down every known side effect, risk factor, and contraindication for hyperbaric oxygen therapy in 2026. We're pulling from peer-reviewed research, clinical data from major medical centers, and the latest safety guidelines from the Undersea and Hyperbaric Medical Society (UHMS). No sugarcoating, no fearmongering. Just what you actually need to know before you step into that chamber.

If you're brand new to HBOT, start with our beginner's guide for a broader overview. Already familiar? Let's get into the risks.

The Most Common Side Effects of Hyperbaric Oxygen Therapy

Let's start with the side effects you're most likely to actually experience. These aren't the scary ones — they're the everyday annoyances that come with breathing pressurized oxygen, and they affect a small but meaningful percentage of patients.

Ear and Sinus Barotrauma

This is the number one side effect. Not even close. A comprehensive study published in Advances in Skin & Wound Care found that ear pain accounted for nearly 50% of all reported adverse events during HBOT (Heyboer et al., 2017). The mechanism is straightforward: as chamber pressure increases during "descent," the air pressure outside your eardrum rises faster than the pressure inside. If you can't equalize — through swallowing, yawning, or the Valsalva maneuver — that pressure differential causes pain, and in some cases, actual injury to the tympanic membrane.

Sinus barotrauma works similarly. The air-filled sinuses in your face need to equalize with the surrounding pressure, and if they can't (because of congestion, polyps, or anatomical variations), you'll feel it. Sharp pain in the forehead, cheeks, or around the eyes is the typical presentation.

The good news: most ear and sinus issues are mild and preventable. Clinics like MD Hyperbaric Chicago train patients on equalization techniques before their first session. Slowing down the pressurization rate — something any competent operator will do if you report discomfort — eliminates the problem for most people.

Who's at higher risk: Anyone with a current upper respiratory infection, allergies with sinus congestion, a history of ear surgery, or eustachian tube dysfunction. If you have a cold, reschedule. Seriously. It's not worth it.

Temporary Vision Changes

This one catches people off guard. After a series of HBOT sessions, some patients notice their vision has shifted — specifically, they develop or worsen myopia (nearsightedness). Research from the UHMS indicates this occurs in a significant minority of patients undergoing extended treatment courses of 20 or more sessions.

The cause is a reversible change in the shape of the lens inside the eye. Prolonged oxygen exposure at elevated pressures causes the lens to become more spherical, which shifts the focal point. It's a well-documented phenomenon, and the key word here is reversible. According to the Mayo Clinic, vision typically returns to baseline within days to weeks after completing treatment (Mayo Clinic, 2025). See why major medical centers stay silent on HBOT for the full institutional-silence analysis.

That said, there's a nuance for patients with pre-existing cataracts. There's some evidence that extended HBOT courses (40+ sessions) can accelerate cataract development in patients who already have early-stage lens changes. This doesn't mean HBOT causes cataracts from scratch — it means if you're already on that path, high-dose oxygen might speed things up. Your ophthalmologist and hyperbaric provider should be communicating if this applies to you.

Fatigue and Lightheadedness

Not every side effect shows up in clinical studies, but talk to people who've done 20+ sessions and you'll hear this consistently: HBOT makes you tired. Sometimes pleasantly so — many patients describe it as a deep, restorative fatigue, like the feeling after a long hike. Others find it more disruptive, especially during the first week of treatment.

The lightheadedness usually hits during decompression (the "ascent" phase at the end of a session) or in the minutes immediately after exiting the chamber. It's generally mild, resolves quickly, and is related to the shift back to normal atmospheric pressure.

Confinement Anxiety and Claustrophobia

The study by Heyboer et al. found that approximately 25% of adverse events were classified as confinement anxiety. This makes sense when you consider what's happening: you're lying inside a pressurized tube, often for 60-90 minutes, unable to leave until the operator decompresses the chamber.

Monoplace chambers (single-person tubes) are more likely to trigger claustrophobia than multiplace chambers (walk-in rooms). If anxiety is a concern for you, look for a clinic with multiplace options or transparent monoplace chambers. Some facilities provide tablets for streaming, communication systems, and even mild sedation protocols for patients with severe claustrophobia.

Serious but Rare Complications: What the Research Actually Shows

Now for the risks that are less common but more consequential. These are the ones your provider should discuss with you during the informed consent process — and if they don't bring them up, that's a red flag.

Oxygen Toxicity and Seizures

This is the big one that people worry about, and rightly so — a seizure during treatment is a genuinely serious event. But let's put the numbers in perspective.

Early estimates placed the seizure rate during therapeutic oxygen exposures at 2.0-3.0 atmospheres absolute at about 1 per 10,000 treatments (0.01%). More recent data, accumulated over the past 15 years of clinical practice, puts the incidence higher — approximately 1 in 2,000 to 3,000 treatments (StatPearls, 2025). That's still rare, but it's not negligible if you're doing a 40-session treatment course.

Oxygen toxicity seizures are caused by the central nervous system's response to supraphysiologic oxygen levels. They're sometimes preceded by warning signs — facial twitching, tunnel vision, tinnitus, nausea, or a feeling of impending doom. Trained operators watch for these signs and will reduce pressure or switch the patient to breathing regular air ("air breaks") at the first indication.

The seizure itself, while frightening, is typically self-limiting. Once the excess oxygen is removed (by decompressing the chamber or switching to air), the seizure stops. There's no evidence that HBOT-induced seizures cause lasting neurological damage in otherwise healthy patients. But they do require careful monitoring, which is why reputable centers like Penn Medicine maintain strict staffing ratios and continuous patient observation during treatments.

Risk factors for oxygen toxicity include: higher treatment pressures (above 2.4 ATA), longer session durations, fever, hyperthyroidism, and certain medications that lower the seizure threshold.

Pulmonary Oxygen Toxicity

Your lungs don't love extended exposure to high concentrations of oxygen either. Pulmonary oxygen toxicity manifests as chest tightness, coughing, and in severe cases, reduced lung function. The mechanism involves oxygen free radicals damaging the delicate alveolar tissue.

Here's the practical reality: at standard clinical HBOT pressures (1.5-2.5 ATA) and durations (60-120 minutes per session), clinically significant pulmonary toxicity is extremely uncommon. It becomes a real concern only with prolonged exposures — think emergency treatments for gas gangrene or carbon monoxide poisoning where patients may receive multiple sessions within 24 hours. See the gas gangrene evidence atlas for the full study-by-study evidence breakdown.

The Undersea and Hyperbaric Medical Society's protocols include built-in air breaks during longer sessions specifically to mitigate this risk. A typical 90-minute session at 2.0 ATA might include two 5-minute air breaks, during which the patient breathes regular air instead of pure oxygen.

Pneumothorax and Air Embolism

These are the rarest and most dangerous complications, and they're almost entirely preventable with proper screening.

A pneumothorax (collapsed lung) can theoretically worsen under hyperbaric conditions because trapped air in the pleural space expands during decompression. This is why an untreated pneumothorax is the only absolute contraindication for HBOT — full stop. If you have one, you cannot go in the chamber until it's resolved.

Air embolism — air bubbles entering the bloodstream — is primarily a risk during rapid decompression or in patients with certain cardiac conditions (specifically, a patent foramen ovale or other right-to-left shunt). Proper decompression protocols essentially eliminate this risk in standard clinical practice.

Dental and Sinus Barotrauma

Beyond ear issues, barotrauma can affect teeth with existing dental work. Air trapped under fillings, crowns, or in areas of tooth decay can expand during pressure changes, causing anything from mild discomfort to cracking. This is uncommon with modern dental materials but worth mentioning to your provider if you have older restorations.

A Frontiers in Medicine systematic review and meta-analysis found that the HBOT group reported significantly more adverse effects overall (30.11%) compared to control groups (10.43%, p < 0.05), though the majority were mild and self-resolving (Wang et al., 2023). This is important context: while the rate of side effects is higher than doing nothing, the severity is generally low.

Who Should NOT Get Hyperbaric Oxygen Therapy: Absolute and Relative Contraindications

Not everyone is a candidate for HBOT. Understanding contraindications isn't about fearmongering — it's about making sure the treatment helps rather than harms. Any responsible clinic will screen for these before your first session.

The One Absolute Contraindication

Medical guidelines are consistent on this point: the only absolute contraindication to HBOT is an untreated pneumothorax (StatPearls, NCBI, 2025). A pneumothorax means air has leaked into the space between the lung and the chest wall. Under increased pressure in the hyperbaric chamber, this trapped air behaves unpredictably during decompression, potentially causing a tension pneumothorax — a life-threatening emergency.

If you have a known pneumothorax, it must be treated (usually with a chest tube) and confirmed resolved before HBOT can proceed. There are no exceptions, no workarounds.

Relative Contraindications: Case-by-Case Decisions

Relative contraindications are conditions where HBOT may still be appropriate, but the decision requires careful evaluation by both your primary care provider and the hyperbaric medicine team. These include:

Pulmonary conditions:

• Chronic obstructive pulmonary disease (COPD) with air trapping
• Severe asthma with poor control
• History of spontaneous pneumothorax
• Pulmonary blebs or bullae (air-filled spaces in the lungs)

These conditions raise the risk of pulmonary barotrauma during pressure changes. Patients with COPD can often still receive HBOT, but may need modified protocols with slower compression and decompression rates.

Cardiovascular concerns:

• Unstable angina or recent myocardial infarction
• Severe congestive heart failure (the increased oxygen can actually worsen fluid overload)
• Known right-to-left cardiac shunt or patent foramen ovale

Medications and treatments:

• Certain chemotherapy agents (notably doxorubicin and cisplatin) may interact poorly with high-dose oxygen
• Bleomycin — even a remote history of bleomycin use is a relative contraindication due to the risk of severe pulmonary toxicity
• Disulfiram (Antabuse) — may block the body's natural defense against oxygen toxicity

Other conditions:

• Uncontrolled seizure disorder — the small risk of oxygen-induced seizures is additive
• Uncontrolled high fever — fever increases the risk of oxygen toxicity
• Active upper respiratory infection — dramatically increases barotrauma risk
• Severe claustrophobia — may make treatment intolerable (though multiplace chambers and sedation protocols can help)
• Pregnancy — not enough safety data to recommend routine use, though it's used in emergency situations like carbon monoxide poisoning

Diabetes is sometimes listed as a relative contraindication, but this is more about monitoring than restriction. HBOT can cause blood sugar drops during treatment. Diabetic patients — particularly those on insulin — need glucose monitoring before and after sessions. Facilities like UI Health have established protocols for managing diabetic patients during HBOT.

Implanted Medical Devices

Certain implanted devices are incompatible with hyperbaric environments. Cochlear implants, some types of pacemakers and defibrillators, and epidural pain pumps may malfunction under pressure. If you have any implanted device, bring the manufacturer's specifications to your HBOT consultation — most modern devices are pressure-rated, but it needs to be verified.

Hard Shell vs. Soft Shell Chambers: Do the Risks Differ?

This is a question that doesn't get enough attention. Not all hyperbaric chambers carry the same risk profile, and the distinction between hard shell (clinical-grade) and soft shell (mild/portable) chambers matters.

Hard Shell Chambers (Hospital and Clinical Grade)

Hard shell chambers operate at pressures between 1.5 and 3.0 ATA and deliver 100% oxygen. These are the chambers used in hospital-based programs and established HBOT clinics. They're FDA-cleared for 14 specific medical conditions, including diabetic wounds, radiation injury, decompression sickness, and carbon monoxide poisoning.

The higher pressures and pure oxygen delivery mean the side effect profile we've been discussing fully applies. Barotrauma risks are real. Oxygen toxicity is a genuine (if rare) concern. But the upside is that these chambers deliver the therapeutic pressures validated in clinical research.

Hard shell chambers require trained operators, emergency protocols, and proper maintenance. The chambers themselves are engineered with multiple safety systems — pressure relief valves, communication systems, fire suppression, and controlled decompression mechanisms.

Soft Shell Chambers (Mild Hyperbaric)

Soft shell or portable chambers typically max out at 1.3 to 1.5 ATA and deliver oxygen concentrations of approximately 24-35% (compared to 100% in hard shell chambers). These are the units marketed for home use and sold by various wellness companies.

The side effect profile is different — and in some ways, that's exactly the problem.

Lower risks: At mild pressures with lower oxygen concentrations, the risks of oxygen toxicity, seizures, and significant barotrauma are substantially reduced. You're unlikely to experience the serious complications associated with clinical HBOT.

But also lower efficacy: The pressures and oxygen concentrations in soft shell chambers fall below the thresholds used in virtually all clinical research supporting HBOT's therapeutic benefits. For context, the majority of peer-reviewed HBOT studies use pressures of 2.0-2.5 ATA with 100% oxygen. At 1.3 ATA with 24% oxygen, you're getting a fundamentally different intervention.

Unique risks of home use: The biggest risk with soft shell chambers isn't the pressure — it's the lack of medical supervision. No one is monitoring you for signs of distress. No one is managing the compression rate if you can't equalize. And critically, there's no trained professional to respond if something goes wrong.

The FDA has issued multiple warnings about unapproved hyperbaric chambers, and some consumer-grade units have been involved in fire incidents (the enriched oxygen environment is highly flammable). For a deeper dive into this comparison, check out our complete guide to HBOT.

How to Minimize Your Risk: Practical Safety Steps

Knowing the risks is step one. Reducing them is step two. Here's what actually moves the needle on safety.

Choose an Accredited Facility

This is the single most important decision you'll make. An accredited facility means:

• Trained staff. The operator should be a Certified Hyperbaric Technologist (CHT) or equivalent. The medical director should be a physician with hyperbaric medicine credentials, ideally board-certified by the American Board of Preventive Medicine in Undersea and Hyperbaric Medicine.
• Maintained equipment. Chambers require regular inspection, testing, and maintenance. Ask when the last safety inspection was performed.
• Emergency protocols. The facility should have written emergency procedures for fire, equipment failure, seizure, and patient decompensation. Ask to see them. If they won't show you, leave.
• UHMS accreditation. The Undersea and Hyperbaric Medical Society accredits clinical hyperbaric programs. It's not the only marker of quality, but it's a strong one.

Communicate Your Full Medical History

Don't leave anything out. Your HBOT provider needs to know about:

• All current medications (including supplements — some, like vitamin E in high doses, affect coagulation under pressure)
• History of ear, sinus, or lung surgery
• Any implanted devices
• Claustrophobia or anxiety disorders
• Pregnancy or possibility of pregnancy
• Recent illnesses, especially respiratory infections
• History of seizures
• Current or past cancer treatment (especially bleomycin)

Learn Equalization Techniques Before Your First Session

Barotrauma is the most common side effect, and it's largely preventable. Practice these techniques before you arrive:

• Valsalva maneuver: Pinch your nose and gently exhale against the closed nostrils. You should feel your ears "pop."
• Toynbee maneuver: Pinch your nose and swallow.
• Frenzel maneuver: Pinch your nose, close your mouth, and push the back of your tongue upward.
• Jaw movement: Simply moving your jaw side to side or opening wide can help equalize pressure.

Start equalizing early and often during compression — don't wait until you feel pain.

Follow Pre-Session Guidelines

Most clinics provide a preparation checklist. The essentials:

• No smoking before treatment. Smoking constricts blood vessels and reduces the oxygen-carrying benefit of treatment. It also increases CO levels in your blood, which works directly against the therapy.
• No alcohol for several hours before. Alcohol affects how your body handles oxygen and pressure changes.
• Avoid carbonated beverages before sessions — the gas can cause discomfort during pressure changes.
• Wear cotton clothing — synthetic materials can generate static electricity, which is a fire concern in oxygen-enriched environments.
• Remove all petroleum-based products — lotions, hair products, certain deodorants. Again, fire risk in high-oxygen environments.
• Eat a light meal before your session. Low blood sugar during treatment can cause dizziness and nausea.

Know When to Speak Up During Treatment

Once you're in the chamber, never tough it out if something feels wrong. Tell the operator immediately if you experience:

• Ear or sinus pain that doesn't resolve with equalization
• Chest pain or difficulty breathing
• Facial twitching, visual changes, or ringing in your ears (signs of oxygen toxicity)
• Severe anxiety or panic
• Nausea
• Any sudden change in how you feel

A competent operator will slow down or stop compression, give you an air break, or abort the session entirely. A good clinic would rather stop a session early than push through a problem.

For more on what to expect during your sessions, our myths debunked article separates common misconceptions from clinical reality.

Long-Term Safety: What Happens After Many Sessions

Most side effect discussions focus on what happens during or immediately after a single session. But many patients undergo 20, 40, or even 60+ treatments. What does the long-term safety profile look like?

The Evidence for Extended Treatment Courses

The good news: there's a reasonable body of evidence on long-term safety, primarily from wound care patients who undergo 30-60 sessions over several months.

Vision changes are the most reliable long-term effect. Myopic shifts of 0.5 to 1.5 diopters are common after 20+ sessions. In the vast majority of cases, vision returns to baseline within 2-8 weeks after the final treatment. However, patients over 50 with pre-existing lens changes may experience accelerated cataract formation that doesn't fully reverse.

No evidence of chronic lung damage at standard clinical protocols. Pulmonary function studies in patients who've completed extended HBOT courses show no lasting decrease in lung capacity or gas exchange efficiency.

No increased cancer risk. This is a question that comes up periodically — does flooding the body with oxygen promote tumor growth? The clinical evidence does not support this concern. Multiple studies have examined cancer patients receiving HBOT for radiation injury (a well-established indication), and none have found increased cancer recurrence rates. A 2022 systematic review published in Cancer Medicine found no evidence that HBOT promotes cancer growth in any tissue type.

Cumulative barotrauma effects are possible. Patients who experience repeated mild ear barotrauma over many sessions can develop chronic middle ear inflammation. This is avoidable with proper technique and doesn't occur in patients who equalize effectively.

The Off-Label Long-Term Question

Here's where things get murkier. The long-term safety data we have comes primarily from patients treated for FDA-cleared indications at established medical centers. The growing population of people using HBOT off-label — for longevity, cognitive enhancement, athletic recovery, and general wellness — represents a newer and less-studied cohort.

Are 100+ lifetime sessions safe? Probably, based on what we know about the mechanisms of harm. But "probably" isn't the same as "proven." If you're planning an extended HBOT program for off-label purposes, establish a relationship with a physician who can monitor for cumulative effects, including periodic vision exams and pulmonary function assessments.

Comparing HBOT Safety to Other Common Medical Treatments

Context matters. Every medical intervention carries risk. Here's how HBOT stacks up against treatments people routinely accept without a second thought.

HBOT vs. Common Procedures

The takeaway: HBOT's risk profile is comparable to — or better than — many commonly used medical interventions. The difference is that those other treatments have decades of cultural normalization behind them. Nobody agonizes over the risk profile of ibuprofen, despite its well-documented GI and cardiovascular risks.

What Makes HBOT Safer Than Its Reputation Suggests

Three factors contribute to HBOT's strong safety record:

1. It's non-invasive. Nothing is injected, implanted, or surgically altered. The primary intervention is breathing — at higher pressure and oxygen concentration, but still just breathing.

2. Side effects are mostly reversible. Unlike surgical complications or medication side effects that can be permanent, nearly all HBOT adverse events resolve completely once treatment stops.

3. Risks are front-loaded. The main risk period is during the treatment session itself, when trained professionals are present and monitoring. There's no "take this pill and hope nothing goes wrong at home" dynamic — complications that are going to happen will happen under medical supervision.

That said — and we keep coming back to this because it matters — these safety advantages apply to supervised clinical HBOT. The safety profile of unsupervised home use, unaccredited facilities, or improvised chamber setups is a different and less reassuring conversation.

Frequently Asked Questions

Is hyperbaric oxygen therapy safe for elderly patients?

Yes, for most elderly patients. Age alone is not a contraindication. However, older adults are more likely to have conditions that require careful screening — cardiovascular disease, COPD, implanted devices, and pre-existing lens changes that could be affected by oxygen exposure. The equalization challenge can also be greater in elderly patients due to stiffer eustachian tubes. A thorough pre-treatment evaluation by a physician experienced in hyperbaric medicine is essential. Many wound care patients who benefit most from HBOT are over 65, and the therapy has a strong safety track record in this demographic.

Can HBOT interact with my medications?

Certain medications do interact with HBOT. The most critical is bleomycin — even a remote history of bleomycin use is a relative contraindication due to the risk of severe pulmonary fibrosis when combined with high-dose oxygen. Cisplatin and doxorubicin can also have enhanced toxicity under hyperbaric conditions. Disulfiram (Antabuse) may block the body's natural defense against oxygen free radicals. Mafenide acetate (Sulfamylon), a topical burn cream, can compound oxygen toxicity risk. Additionally, insulin dosing may need adjustment because HBOT can lower blood sugar. Always provide your complete medication list — including supplements and OTC medications — to your hyperbaric provider before starting treatment.

How often do serious complications like seizures actually occur?

Oxygen toxicity seizures occur in approximately 1 in 2,000 to 3,000 treatments based on recent data from clinical practice (StatPearls, 2025). To put that in practical terms: if you're doing a standard 40-session treatment course, your probability of experiencing a seizure during the entire course is roughly 1-2%. These seizures are self-limiting — they stop when the oxygen concentration is reduced — and there's no evidence they cause lasting neurological harm. Life-threatening complications like tension pneumothorax or arterial gas embolism are extraordinarily rare in properly screened patients at accredited facilities, with incidence rates below 1 in 100,000 treatments.

Are soft shell home chambers safer than clinical hard shell chambers?

In terms of immediate physical risk, yes — soft shell chambers operate at lower pressures (1.3-1.5 ATA) with lower oxygen concentrations (24-35%), which substantially reduces the risks of barotrauma, oxygen toxicity, and seizures. However, they introduce different risks: no medical supervision means no one to respond to emergencies, and the enriched oxygen environment creates fire hazards that home users may not properly mitigate. The FDA does not clear soft shell chambers for treating any medical condition, and several consumer units have been involved in safety incidents. Lower risk isn't the same as no risk, and the absence of professional monitoring is itself a significant risk factor.

Should I be worried about long-term effects from multiple HBOT sessions?

For most patients undergoing standard treatment courses (20-40 sessions), the long-term safety data is reassuring. Vision changes are the most common lingering effect and typically resolve within 2-8 weeks after treatment ends. There's no evidence of chronic lung damage, increased cancer risk, or cumulative neurological effects at standard clinical protocols. The less-studied scenario is very extended use — 100+ lifetime sessions for off-label purposes like longevity or wellness. While the theoretical risk remains low, this population hasn't been studied with the same rigor. If you're planning extended HBOT use, periodic monitoring (vision exams, pulmonary function tests) is a sensible precaution.

Related Reading

• The Complete Guide to Hyperbaric Oxygen Therapy [2026] — Everything from how it works to what conditions it treats, all in one place.
• HBOT Myths Debunked: Separating Fact from Fiction [2026] — Common misconceptions about HBOT and what the science actually says.
• HBOT for Beginners: What to Know Before Your First Visit — A practical walkthrough for first-time patients.

-- The HBOT Finder Team