In 1.5 million tracked HBOT sessions, only 0.68% caused any adverse event. The most common side effect is ear barotrauma, hitting 9 to 15% of patients, almost half of those cases mild and self-resolving. Oxygen toxicity seizures, the complication patients fear most, occurred zero times across 16,430 sessions at 2.0 ATA. Risk is real but quantifiable, and lower than most patients expect.
Most Common Hyperbaric Chamber Side Effects
Most side effects are mild and transient. Here is what the clinical data shows for each complication, ranked by frequency.
Ear Pressure and Barotrauma
The most common side effect is middle ear barotrauma, ear pain or pressure caused by difficulty equalizing pressure as the chamber compresses. It affects approximately 9–15% of patients across large studies, making it the dominant complication by frequency.[2]
Most cases are mild. Of 18,284 patients studied in a 2025 systematic review, 42.8% of ear-related complications were mild (Grade 1) and only 6.4% were severe.[2] Only about 1.5% of all HBOT patients needed to discontinue treatment because of ear complications.
What to do: Learn the Valsalva maneuver (pinch your nose and blow gently), yawning, and swallowing before your first session. Alert technicians immediately if you cannot equalize during compression. Slow compression rates significantly reduce severity of barotrauma.[5]
Higher risk factors: female sex, age over 55, head and neck conditions, previous ear surgery, upper respiratory infection, and sensory neuropathy.[2]
Vision Changes
Temporary myopia (nearsightedness) is common during multi-week HBOT courses. The high-pressure oxygen environment affects lens shape and refractive index. Some patients notice their distance vision changes enough to require a different glasses prescription during treatment. This is almost always transient and resolves days to weeks after completing the treatment course. Permanent vision changes from HBOT are not documented in large clinical studies.[6]
Fatigue, Headache, and Nausea
Many patients feel unusually tired after sessions, particularly in the first week of treatment. Mild headaches and occasional nausea occur, especially during longer sessions. These are generally self-limiting and diminish as patients acclimate to treatment.
Serious Side Effects and When to Worry
Oxygen Toxicity
Oxygen toxicity occurs when excessive oxygen causes damage to the lungs (pulmonary toxicity) or brain (CNS toxicity, presenting as seizures). Both are rare at properly supervised therapeutic pressures.[1]
CNS oxygen toxicity (seizures): Across 16,430 sessions at 2.0 ATA in one study, zero seizures occurred. Seizure rates increase substantially above 2.0 ATA: 15 per 10,000 sessions at 2.4–2.5 ATA and 51 per 10,000 at 2.8 ATA in the same dataset.[3] Five-minute air breaks every 25–30 minutes reduce seizure frequency from 3.9 to 1.2 per 10,000 sessions, a statistically significant protective effect.[7]
Pulmonary oxygen toxicity: Presents as chest tightness, persistent cough, or difficulty breathing. Occurs primarily with very high cumulative oxygen doses. Clinical protocols include air breaks specifically to prevent this complication.
Pneumothorax
Lung collapse (pneumothorax) is the rarest serious complication. In the largest dataset of 1.5 million treatments, only one confirmed case of pneumothorax was documented.[1] An untreated tension pneumothorax is the only absolute contraindication to HBOT, because pressurization would worsen the condition.
Who Should Avoid Hyperbaric Chambers
Absolute contraindication (must not undergo HBOT):
- Untreated tension pneumothorax
Relative contraindications (require individual evaluation):
- Severe COPD with CO2 retention
- Uncontrolled seizure disorders (note: a 2025 study found HBOT safe in patients with seizure history using proper protocols: 1 seizure in 634 sessions)[8]
- Acute viral infection
- Pregnancy (no safety data available)
- Recent ear surgery
- Active upper respiratory infection
- Certain chemotherapy agents: bleomycin, cisplatin, doxorubicin, disulfiram
- Optic neuritis
- Uncontrolled high fever
Long-Term Safety: What the Evidence Shows
Large retrospective studies support a strong long-term safety profile. A 2016 analysis of 2,334 patients found that when strict protocols are followed, HBOT can be considered one of the safest medical treatments available today.[6] The per-session adverse event rate of 0.68% compares favorably with common medical procedures including colonoscopy (0.01–0.3% perforation risk) and NSAID use (1–4% GI complication rate per year).[1]
Fire risk in the treatment environment is a safety concern separate from physiological side effects. Facilities must comply with NFPA 99 Chapter 14 requirements, prohibiting electronics, synthetic fabrics, and petroleum-based products in chambers. Patients must follow all pre-session screening protocols. See our guide on hyperbaric chamber fire safety for details.
How to Minimize Side Effects
- Learn equalization techniques before your first session. Ask your provider to demonstrate the Valsalva maneuver, yawning, and swallowing. Practice them before entering the chamber.
- Report ear pain immediately. During compression, if you cannot equalize, alert the technician. Stopping compression briefly prevents mild discomfort from becoming barotrauma.
- Disclose all medications and conditions. Some drugs and conditions increase risk of specific complications. Your provider screens for these, but only if you provide accurate information.
- Do not enter the chamber with congestion. Upper respiratory infections significantly increase barotrauma risk. Reschedule if you are unwell.
- Follow all personal item protocols. No electronics, synthetic clothing, deodorant, or petroleum-based products. These protocols exist because they directly reduce fire risk in an oxygen-enriched environment.
Frequently Asked Questions
Are hyperbaric chamber side effects permanent?
Most are not. Vision changes, ear pressure, and fatigue are transient. Permanent hearing loss from HBOT is not documented in large clinical studies. The rare serious complication (pneumothorax, severe oxygen toxicity) can have lasting effects but occurs at a rate of under 1 in 10,000 sessions in properly supervised settings.[1]
Is HBOT safe for someone with a history of seizures?
With appropriate precautions, potentially yes. A 2025 study found only 1 seizure in 634 HBOT sessions in patients with seizure history when proper protocols were followed.[8] Uncontrolled seizure disorders remain a relative contraindication. The decision requires individual evaluation by a physician familiar with both the patient’s history and HBOT.
Do children have more side effects from HBOT?
Children under 16 have a higher rate of ear barotrauma compared to adults in large studies.[6] Pediatric HBOT requires particular attention to ear pressure management and session monitoring. Clinical programs routinely treat pediatric patients but require additional safety considerations.
References
- Jokinen-Gordon H, Barry R, Watson B, Covington DS. A retrospective analysis of adverse events in HBO therapy (2012-2015). Advances in Skin & Wound Care. 2017. DOI: 10.1097/01.ASW.0000508712.86959.c9. PMID: 28198743
- Voigt A, Laspro M, Thys E, Jethanamest D, Chiu ES. Systematic Review of Otologic Adverse Events in HBOT. Undersea & Hyperbaric Medicine. 2025. DOI: 10.22462/736. PMID: 41429031
- Heyboer M, Jennings S, Grant W, et al. Seizure incidence by treatment pressure in patients undergoing HBOT. Undersea & Hyperbaric Medicine. 2014;41(5):379-385. PMID: 25558546
- Zhang Y, Zhou Y, Jia Y, Wang T, Meng D. Adverse effects of HBOT: systematic review and meta-analysis. Frontiers in Medicine. 2023;10:1160774. DOI: 10.3389/fmed.2023.1160774. PMID: 37275378
- Mirasoglu B, Cakkalkurt A, Cimsit M. Complication of HBOT: symptomatic middle ear and cranial sinus barotrauma. 2017. DOI: 10.18017/IUITFD.308489
- Hadanny A, Meir O, Bechor Y, Fishlev G, Bergan J, Efrati S. The safety of hyperbaric oxygen treatment — retrospective analysis in 2,334 patients. Undersea & Hyperbaric Medicine. 2016. PMID: 27265988
- Costa DA, Ganilha JS, Barata PC, Guerreiro F. Seizure frequency in more than 180,000 HBOT sessions. Diving and Hyperbaric Medicine. 2019;49(3):167-174. DOI: 10.28920/dhm49.3.167-174. PMID: 31523791
- Park S, Marinov A, Clarke H, et al. Safety of HBOT in non-emergent patients with a history of seizures. PLoS ONE. 2025;20(1):e0317586. DOI: 10.1371/journal.pone.0317586. PMID: 39808603
Medical Disclaimer
The content on BaricBoost.com is for informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
Author
Seph Fontane Pennock is the founder of BaricBoost.com and Regenerated.com, a clinic directory for regenerative medicine serving 10,000+ providers across the United States. He previously built and sold PositivePsychology.com, which grew to 19 million users and became the largest evidence-based positive psychology resource on the web. Seph brings direct experience as an HBOT patient, having completed protocols at clinics across three continents while navigating mold illness, systemic inflammation, and autoimmune conditions. His treatment journey includes hyperbaric oxygen therapy, peptide protocols, NAD+ therapy, and consultations with specialists from Dubai to Cape Town to Mexico. This combination of entrepreneurial track record and lived patient experience shapes everything published on BaricBoost.com. Every article is grounded in peer-reviewed research, informed by real clinical encounters, and written for patients making high-stakes treatment decisions. Seph's focus is on bringing transparency, scientific rigor, and practical guidance to the hyperbaric oxygen therapy space.
