HBOT is generally safe when delivered at UHMS-accredited centers, but it is not without risk. The common side effects are mild and reversible. The rare serious harms can be life-threatening.
This guide is a clear-eyed safety review. We cover the typical side effects, the rare serious risks, what makes HBOT risky when done wrong, and how to weigh safety for your case.
The frame: HBOT carries real risk that varies with pressure, session count, and clinic standards. Hospital programs under UHMS oversight are far safer than unaccredited operators.
Common side effects (1 in 5 patients or more)
Ear injury — ear barotrauma — is by far the most common HBOT side effect. The UHMS safety guidelines 2023 report ear injury in roughly 20 to 30% of patients across HBOT protocols.
Ear pressure changes during compression and decompression. Patients who cannot equalize ear pressure with yawning, swallowing, or Valsalva develop pain. In some cases the eardrum can tear — see our ear equalization guide for technique.
Sinus pain and pressure follow a similar mechanism. Patients with active sinus infection or chronic sinusitis are at higher risk. Most clinics screen for active sinus issues before starting protocols.
Fatigue after sessions is common. Patients often feel tired for several hours after their first 5 to 10 sessions. The fatigue usually resolves as the body adapts.
Less common side effects (1 in 50 to 1 in 100)
Short-term vision change. Many patients experience temporary myopia (nearsightedness) after 20 to 40 sessions. Vision typically returns to baseline within weeks to months after the protocol ends (Plafki et al., Aviat Space Environ Med 2000).
Confinement anxiety. Some patients struggle with monoplace chamber claustrophobia. Sedation and pre-session counseling help most cases — see our chamber anxiety guide.
Numbness or tingling. Mild peripheral nervous system effects occur in some patients. Usually transient.
Rare but serious adverse events
Oxygen-related harm. Hyperoxia at protocol pressures can cause CNS toxicity — seizures — in 1 to 4 per 10,000 sessions (Plafki et al., 2000). The risk rises with pressure (above 2.4 ATA) and session duration.
Lung harm — inflammation from too much oxygen — is dose-driven. Session counts above 60 at higher pressures raise the risk. Patients with prior lung disease start at higher baseline risk.
Chamber fire is the most serious adverse event. The FDA Healthcare Provider letter 2014 documented multiple chamber fire incidents, several fatal. Lithium batteries, oils, synthetic fabrics, and static-prone clothing inside chambers are the main fire triggers.
Decompression sickness during exit. Rare but documented. Typically affects patients with patent foramen ovale or other cardiac shunts. See the decompression sickness evidence atlas for the full study-by-study evidence breakdown.
Who should not get HBOT
Some patients should avoid HBOT entirely. Untreated pneumothorax is a no-go — pressure changes can be deadly.
Patients on certain chemo drugs face raised lung harm risk. Cisplatin, bleomycin, doxorubicin, and disulfiram are the most cited. Talk to your oncologist before any HBOT plan.
Severe COPD, prior chest radiation, and other major lung disease raise harm risk. Some clinics will treat with shorter protocols; others will decline.
Pregnancy is a relative caution. HBOT in pregnancy is reserved for clear medical needs — CO poisoning being the main one. It is not for off-label use. See the carbon monoxide poisoning evidence atlas for the full study-by-study evidence breakdown.
The UHMS Indications Manual 2023 has the full no-go list.
Why UHMS-accredited clinics are safer
A key safety point. UHMS-accredited centers are audited by outside teams on safety steps, staff training, chamber upkeep, fire protocols, and crisis response.
Unaccredited wellness clinics vary widely. Some have full safety steps and trained staff, while others have minimal training and lax fire steps. The lack of accreditation does not prove a clinic is unsafe, but it removes an outside quality check.
For more on UHMS accreditation, see our accreditation explainer. For clinic warning signs, see our clinic red flags article.
How pressure and session count affect risk
A clear pattern. Risk rises with both pressure and total session count.
At 1.3 ATA (mild HBOT), ear injury and confinement anxiety are the main risks. Oxygen-related harm and fire risk are very low.
At 2.0 to 2.5 ATA (medical HBOT), all risks rise. Oxygen-related harm is rare but real, and ear injury rates are higher. Fire risk is also higher because the chamber has more oxygen.
At 2.4 to 3.0 ATA (specific indications), CNS toxicity risk rises further. Single-session protocols at these pressures (CO poisoning, decompression sickness) accept the higher risk because the indication justifies it.
Session count matters because some risks accumulate. Pulmonary harm scales with total exposure. Cataract progression scales with session count above 150 to 200.
Patient-side risk reduction
Things patients can do to reduce risk.
First, choose a UHMS-accredited clinic when possible. Independent accreditation is a quality check that unaccredited clinics do not have.
Second, follow pre-session safety steps. Do not wear synthetic fabrics, do not bring electronics inside the chamber, and follow the clinic's pre-session checklist exactly.
Third, report ear pain or sinus pain immediately. Pain that is ignored becomes ear injury that requires medical attention.
Fourth, ask about prior fire incidents. Reputable clinics will discuss their safety record and protocols openly.
Long-term safety considerations
Most HBOT side effects are reversible. The exceptions are worth noting.
Cataract progression. Long-term HBOT — above 200 sessions in some series — has been linked to faster cataract formation. The cause is oxygen-related stress on the lens.
Repeated ear injury can lead to chronic ear tube problems. Patients who keep struggling to equalize during sessions may develop lasting hearing or balance issues.
Long-term outcomes from off-label HBOT — 60-session anti-aging protocols, multi-year recovery protocols — are not well-studied. The available data covers short-term safety, not 5-year or 10-year outcomes.
What major medical organizations say
The position from mainstream medicine.
The FDA has issued a 2014 consumer alert on off-label HBOT marketing. The agency's position: HBOT is safe and effective for the 13 cleared indications when delivered by trained staff at accredited facilities.
UHMS publishes safety standards updated regularly. UHMS-accredited centers commit to these standards as a condition of accreditation.
Academic medical center pages — Cleveland Clinic, Mayo, Hopkins — describe HBOT safety in measured terms (Cleveland Clinic HBOT overview 2024). The shared frame: safe when delivered at accredited centers, with real but manageable risks.
For broader context on what mainstream medicine endorses (and what it does not), see our institutional silence analysis.
A reasonable patient framework
If you are considering HBOT, three steps for safety.
First, confirm your indication is on the FDA-cleared list or has documented evidence for off-label use. Risk-benefit math is different for an FDA-cleared use than a speculative one.
Second, choose a UHMS-accredited clinic if available. If not, ask about chamber make and model, staff training, fire protocols, and prior safety incidents.
Third, follow all pre-session safety steps. Do not bring electronics or wear synthetic fabrics. Report ear or sinus pain immediately.
Bottom line
HBOT is generally safe when delivered at UHMS-accredited clinics. Ear injury is common but manageable, while oxygen-related harm and seizures are rare. Chamber fire is the worst outcome but is preventable with proper protocols.
The risk profile rises with pressure and session count. Mild HBOT at 1.3 ATA carries lower risk than medical HBOT at 2.4 ATA, but lower clinical effect for FDA-cleared indications.
For any HBOT decision, start by mapping the indication to the FDA list. Match the indication to the appropriate care tier, then verify the clinic against UHMS standards. Follow all safety protocols.
Related Reading
- Oxygen toxicity in HBOT: real risks explained
- HBOT side effects: ear pain, fatigue, and eye changes
- HBOT clinic red flags: signs of unsafe practice
- UHMS-accredited HBOT facilities: what certification means
- FDA-cleared HBOT chambers: complete list
Frequently asked questions
What is the most common HBOT side effect?
Ear injury (ear barotrauma) is the most common, affecting 20 to 30% of patients. It is usually mild and reversible with proper equalization technique.
Can HBOT cause seizures?
Yes, oxygen-related CNS toxicity can cause seizures at higher pressures. The risk is 1 to 4 per 10,000 sessions. Risk rises with pressure above 2.4 ATA and longer session duration.
Is chamber fire a real risk?
Yes. The FDA has documented multiple chamber fire incidents in the US, some fatal. Fire risk rises with the elevated oxygen environment. Strict fire-prevention protocols reduce but do not eliminate the risk.
Who should not get HBOT?
Patients with untreated pneumothorax should avoid HBOT entirely. Those on certain chemo drugs face raised lung toxicity risk. Severe pulmonary disease is a relative caution. Pregnancy is a relative caution for off-label use.
How can I reduce my HBOT risk?
Choose a UHMS-accredited clinic, follow all pre-session safety steps, do not bring electronics or synthetic fabrics into the chamber, and report ear or sinus pain immediately.
Medical disclaimer: This guide is informational and does not constitute medical advice. HBOT carries real risks including ear injury, oxygen-related harm, and chamber fire. The FDA has cleared HBOT for 13 specific uses; uses outside that list are off-label. Discuss any HBOT plan with a doctor trained in hyperbaric medicine before starting.
-- The HBOT Finder Team