People weighing hyperbaric oxygen therapy (HBOT) often ask about long-term effects. The honest answer is that the side-effect profile is well understood for the standard 30-40 session protocol used in FDA-approved care. Longer protocols, repeat courses, and off-label use have less data behind them.
We pulled the major safety reviews, FDA notices, and patient registries to summarize what is known. The FDA has cleared HBOT for 13 specific uses.
These have decades of safety data. Off-label uses do not.
For most patients on a standard protocol at a UHMS site, long-term effects are not the main concern. The main concerns are acute and addressable.
Acute side effects
The most common acute side effect is middle-ear ear injury. The Heyboer 2017 review of 1,148 patients across multiple centers found ear ear injury in roughly 2% of HBOT sessions. Most cases were mild — discomfort or transient hearing change that resolved.
Sinus ear injury is less common but follows similar patterns. Patients with active upper airway infections are at higher risk and should defer sessions when sick.
Lung oxygen harm is rare in standard HBOT protocols. The risk rises with very long sessions or daily sessions for many weeks. Air breaks during sessions reduce this risk.
Central nervous system oxygen harm (oxygen seizures) is the most serious acute risk. Modern protocols at 2.0-2.4 ATA see this at roughly 1 in 10,000 sessions (Plafki 2000).
Claustrophobia in monoplace chambers affects roughly 5% of patients. Most can adapt with reassurance and pre-drug if needed.
The chamber fire risk
The FDA issued a 2021 letter to health care providers warning about chamber fires. The letter highlighted several incidents at non-medical hyperbaric facilities.
The mechanism is straightforward. High-oxygen environments lower the ignition temperature of flammable materials. Static electricity, electronic devices, or oil-based products can trigger fires.
In hospital wound programs running hard-shell Sechrist Industries or Perry Baromedical chambers, strict pre-session protocols (cotton gowns only, no electronics, no flammable products) make fire very rare. Soft-shell wellness chambers from OxyHealth or Summit to Sea at sites like Restore Hyper Wellness should follow the same safety protocols. Some independent operators have been less rigorous, which is what prompted the FDA letter.
Look up any chamber's K-number on openFDA. Verify the safety protocol with the clinic before starting.
For more detail on fire safety, see our HBOT safety checklist.
Added-up oxygen harm
Oxygen harm is not a single threshold. Both lung and CNS harm are added-up across sessions, most of all at higher pressures and longer durations.
The Unit Lung Toxic Dose (UPTD) framework is the standard metric for added-up lung effects. Most HBOT protocols stay well below the toxic threshold. Some anti-aging protocols promoted by off-label clinics push closer to it.
The CNS oxygen harm threshold drops with added-up exposure. A patient who has had a seizure during one session is at higher risk for future sessions. Most programs will adjust protocols or stop HBOT entirely after a seizure event.
For standard 30-40 session protocols at 2.0-2.4 ATA, added-up harm stays within established safe limits. Extended protocols of 60+ sessions, particularly those marketed for anti-aging by some clinics, approach less-studied territory.
Aviv Clinics, for example, runs a 60-session protocol at 2.0 ATA. The Sagol Center research backing this protocol (Hadanny et al. 2020) reports good safety in the trial cohort. The data is limited to single-center research; multi-center safety data at this dose is thinner.
Long-term effects on visual function
Myopic shift — a temporary worsening of nearsightedness — is well noted in patients on extended HBOT protocols (Khan & McLean 2005). The change usually reverses within several weeks of stopping HBOT.
Cataract formation has been reported in some long-course HBOT patients. The risk appears to rise with added-up oxygen exposure. The UHMS safety committee has commented on this risk.
For standard 30-40 session protocols, post-HBOT vision changes usually reverse. For extended anti-aging protocols of 60+ sessions, the research is less clear.
Patients with existing eye conditions, most of all diabetic retinopathy, should discuss HBOT with their ophthalmologist before starting.
Effects on cancer risk
A common patient concern: does HBOT promote tumor growth? The published research does not support this concern at standard protocols.
The Moen & Stuhr 2012 review examined the evidence for HBOT and cancer in detail. The conclusion: HBOT does not increase tumor incidence, recurrence, or progression in published data.
Active cancer is not an absolute contraindication for HBOT when an FDA-approved indication exists. Patients with radiation injury from cancer treatment often need HBOT alongside ongoing cancer follow-up. See the late radiation tissue injury evidence atlas for the full study-by-study evidence breakdown.
The discussion should include the patient's oncologist. For more on radiation tissue damage treatment, see our HBOT for radiation tissue damage review.
Effects on cognitive function
This is where off-label HBOT marketing gets aggressive. Several clinics market HBOT for cognitive enhancement, anti-aging, and brain health.
The published research on cognitive effects of HBOT is mixed. The Sagol Center work shows cognitive gains in older adults on the 60-session protocol. The HOPPS and BIMA TBI trials show no benefit over sham in younger military groups.
What we can say with confidence: a standard 30-40 session course at 2.0-2.4 ATA does not produce noted long-term cognitive harm. Whether it produces lasting cognitive benefit is unsettled.
We unpack the cognitive-marketing gap in our Aviv evidence-vs-marketing analysis and our HBOT for ADHD evidence review.
Effects on blood sugar in diabetic patients
HBOT can lower blood glucose during and after sessions. Patients on insulin or oral hypoglycemics should monitor blood sugar closely, most of all in the first week of treatment.
The effect usually appears within the first few sessions and stabilizes. Adjustments to diabetic drugs may be needed during the HBOT course.
For diabetic foot ulcer patients — the largest FDA-approved indication — the glucose effect is generally a benefit. Lower glucose supports wound healing.
For more on diabetic protocols, see our HBOT 40-session protocol explainer.
Repeat courses
Some patients ask about repeat HBOT courses — completing one 40-session protocol, then later doing another. The safety data on this is thin.
For FDA-approved uses, repeat courses are usually driven by clinical need (e.g., recurrent radiation injury). Most UHMS programs will offer them with appropriate monitoring.
For off-label uses, most of all anti-aging and anti-aging, multiple courses become more speculative. There is no published safety data for, say, 200 added-up HBOT sessions across multiple courses at 2.0 ATA.
A reasonable practice: limit added-up session counts. Discuss any repeat course with a UHMS-certified hyperbaric physician before starting.
The institution silence pattern
Major academic medical centers in the US do not promote HBOT for long-term "wellness" or "anti-aging" use. They use HBOT only for FDA-approved uses. See why major medical centers stay silent on HBOT for the full institutional-silence analysis.
This is the same pattern we cover in our institution silence on HBOT analysis. Research centers see the same data the wellness market sees. They have not adopted off-label HBOT as standard care.
That choice reflects, in part, the gap in long-term safety data for extended off-label protocols.
What we don't know
Several open questions remain.
Long-term cardiovascular effects past 100+ added-up sessions: thin data.
Effects on bone marrow stem cell groups: emerging research from the Sagol Center suggests changes, but the clinical significance is unclear.
Pregnancy: HBOT is sometimes given for carbon monoxide poisoning in pregnant patients. Routine use during pregnancy for other uses is not recommended.
Children: pediatric HBOT for FDA-approved uses has decades of data. Long-term off-label use in children is undertested. See our pediatric HBOT overview.
How to minimize risk
Several practices reduce both acute and long-term risk.
Use a UHMS site. Check the UHMS directory. UHMS audits cover safety.
Use a hard-shell FDA-cleared chamber for clinical uses. Sechrist Industries and Perry Baromedical are the standard manufacturers.
Limit protocol length. The standard 30-40 sessions has the most safety data. Longer protocols carry higher added-up oxygen exposure.
Have an ear/nose/throat evaluation before starting if you have a history of sinus or ear problems. The right pre-treatment can prevent the most common acute complication.
Tell every prescriber. Drugs that affect oxygen utilization or seizure threshold may interact. See our HBOT and drug interactions article.
Bottom line
For a standard 30-40 session HBOT course at a UHMS site, the long-term effects are well understood and manageable. Acute side effects (ear, sinus, occasional vision change) are common but usually mild and reversible.
For extended protocols of 60+ sessions or repeat courses, the data is thinner. Added-up oxygen harm becomes a meaningful concern. The marketing of these protocols by some anti-aging clinics outpaces the safety evidence.
For the 13 FDA-approved uses, the benefit-risk balance is favorable and decades of data support routine use. For off-label uses, the long-term risks have not been studied in detail.
Related Reading
- HBOT side effects and safety
- HBOT safety checklist: red flags and what to verify
- HBOT and drug interactions to know
- Aviv Clinics: evidence vs marketing
- Institutional silence on HBOT
Frequently asked questions
How long do HBOT side effects last?
Most acute side effects (ear pressure, sinus discomfort, mild vision change) resolve within days to weeks of finishing treatment. Persistent effects are uncommon for standard 30-40 session protocols.
Does HBOT cause cancer?
Published research does not support this concern at standard protocols. The Moen & Stuhr 2012 review found no increased cancer incidence, recurrence, or progression with HBOT.
Is it safe to do multiple HBOT courses?
For FDA-approved uses with clinical need, repeat courses are common practice at UHMS sites. For off-label anti-aging use, added-up safety past 100+ sessions is undertested.
What's the chamber fire risk?
Real but very low at sites that follow protocols. Hospital-based UHMS sites have well-established safety protocols. The FDA's 2021 healthcare provider letter focused on non-medical sites with weaker safety culture.
Are there permanent vision changes?
Temporary myopic shift is common during HBOT and reverses within weeks. Cataract risk may rise with very long protocols. Pre-existing eye conditions warrant ophthalmologist consultation before starting.
Medical disclaimer: This article is informational and does not constitute medical advice. HBOT carries real risks including ear ear injury, oxygen harm, and chamber fire. Discuss any HBOT plan with a doctor trained in undersea and hyperbaric medicine before starting, and tell every prescriber about your HBOT course. The FDA has cleared HBOT for 13 specific uses; uses outside those are off-label and have less long-term safety data.
-- The HBOT Finder Team