The most common HBOT side effects are mild and reversible. Ear pain, post-session fatigue, and temporary vision change account for the majority of patient complaints. This guide covers what to expect, why these effects happen, and when to escalate.
This is a patient-facing companion to our broader HBOT safety guide and our oxygen-related harm explainer. It is not exhaustive — it focuses on the three most common side effects that send patients seeking information.
We will cover each in turn: what it is, why it happens, what to do about it, and when to ask your clinic for help.
Ear pain: the most common side effect
Ear pain affects 20 to 30% of HBOT patients (UHMS safety guidelines 2023). It is by far the most common reason patients drop out of HBOT protocols.
The cause is straightforward physics. As the chamber pressurizes, air pressure rises outside the eardrum faster than inside the middle ear. The middle ear has to equalize through the eustachian tube — the small canal connecting the middle ear to the back of the throat.
Most adults can equalize easily by yawning, swallowing, or using the Valsalva maneuver (Mirasol et al., Diving Hyperb Med 2019). Patients with sinus issues, allergies, or anatomical eustachian tube problems may struggle.
When equalization fails, ear pain develops within seconds. Continued descent without equalization can rupture the eardrum. Most clinics will pause descent and instruct the patient on equalization technique before continuing.
For specific equalization technique, see our ear equalization guide.
How to manage ear pain
A practical approach. Prevention is more effective than treatment. Several steps reduce ear pain risk.
Slow your descent. If you feel pressure building, ask the technician to pause. Most clinics will slow descent to give you more time to equalize.
Use Valsalva early. Start equalizing as soon as the descent begins, not when you feel pain. The pressure differential builds quickly and pain can develop in seconds.
Treat sinus issues before sessions. If you have a cold, sinus infection, or active allergies, postpone sessions until cleared. Some clinics use decongestants pre-session for chronic sinus issues.
If ear pain persists, stop the session. Ear injury — ear barotrauma — requires medical care, typically an ENT evaluation. Most cases resolve without permanent hearing loss, but checking is important. See the sudden sensorineural hearing loss evidence atlas for the full study-by-study evidence breakdown.
Fatigue: real but usually temporary
Post-session fatigue is reported by most HBOT patients in the first 5 to 10 sessions (Heyboer et al., Adv Wound Care 2017). The fatigue typically peaks 2 to 4 hours after the session and resolves within 12 to 24 hours.
The mechanism is not fully understood. The leading hypotheses involve oxygen-related stress on tissues, transient changes in cerebral blood flow, and metabolic adaptation to the elevated PO2 environment.
Most patients adapt by session 10. Fatigue diminishes as the body adapts to the cycle of hyperoxia and normoxia. Patients who experience ongoing severe fatigue beyond session 15 should discuss it with their clinic.
A few patients report energy gains instead of fatigue. The variation is real and not predictable based on baseline characteristics. Some patients feel energized post-session, some feel fatigued, and a minority feel essentially no change.
How to manage HBOT fatigue
A simple framework. Plan low-energy days during the first 2 weeks of the protocol. Schedule sessions when you do not need to drive or perform demanding tasks afterward.
Stay hydrated. The protocol involves repeated exposure to dry compressed air. Many patients report mild dehydration that compounds fatigue.
Eat before sessions. Going into HBOT on an empty stomach can amplify fatigue. A light meal 1 to 2 hours pre-session is generally recommended (Cleveland Clinic HBOT prep guide 2024). See why major medical centers stay silent on HBOT for the full institutional-silence analysis.
If fatigue persists or worsens. Discuss with your clinic. Persistent severe fatigue may indicate something other than HBOT — anemia, hypoglycemia, or another underlying issue.
Eye changes: a quirky but well-documented effect
Many patients notice their vision changes during the course of a 40-session HBOT protocol. The most common change is temporary nearsightedness (myopia) that develops after 20 to 30 sessions.
The mechanism is changes to the crystalline lens of the eye. Long-term hyperoxia changes lens hydration and refractive index, which alters the focal length. This is real, well-documented, and reversible (Plafki et al., Aviat Space Environ Med 2000).
Patients typically notice they need stronger reading glasses or that their distance vision is blurrier. The degree of change varies — most report 0.5 to 1.5 diopters of additional myopia by the end of a 40-session protocol.
Vision typically returns to baseline within weeks to months after the protocol ends. Full reversal can take up to 6 months. Some patients elect to skip glasses prescription changes until the post-protocol stabilization period is complete.
Cataract progression: the long-term concern
A separate, less common eye effect. Long-term high-session HBOT — above 150 to 200 sessions across multiple protocols — has been linked to faster cataract progression in some patients (Palmquist et al., Br J Ophthalmol 1984).
The mechanism involves oxidative damage to lens proteins. The risk appears dose-dependent on cumulative session exposure rather than per-session exposure.
For patients pursuing standard 40-session protocols, cataract risk is minimal. For patients pursuing repeated long protocols (60+ sessions repeated annually for several years), the risk is real and warrants periodic ophthalmologic evaluation.
The off-label 60-session anti-aging protocols popularized by some clinics raise cumulative cataract exposure. The trade-off should be discussed with patients pursuing those protocols.
Less common but reportable side effects
Several less common side effects round out the list.
Sinus pressure and pain. Similar mechanism to ear pain — patients with active sinus issues face higher risk. Decongestants and sinus rinse routines reduce risk.
Numbness or tingling. Mild peripheral nervous system effects are reported in a small fraction of patients. Usually transient and resolves with continued sessions.
Confinement anxiety. The chamber experience can trigger claustrophobia, particularly in monoplace chambers. See our chamber anxiety guide for management.
Mild seizure-warning symptoms. Twitching, brief vision changes, or muscle jerks during sessions can precede CNS oxygen harm. Report any unusual symptoms immediately — see our oxygen-related harm explainer for details.
When to escalate to the clinic
A clear list of situations that warrant immediate clinical attention.
Severe or persistent ear pain. Could indicate ear injury (ear barotrauma) requiring ENT evaluation.
Sudden hearing loss or ringing in the ear. May indicate inner ear injury, which is rarer but more serious than outer or middle ear injury.
Significant vision changes beyond mild blurring. Most HBOT vision changes are gradual and mild. Sudden or severe changes are not typical.
Seizure-warning symptoms during sessions. Twitching, anxiety, tunnel vision, or muscle jerks during HBOT may precede CNS oxygen harm.
Persistent severe fatigue. Most patients adapt by session 10. Fatigue that is worse than baseline by session 15 should be discussed.
Chest pain or shortness of breath. Could indicate lung-related oxygen harm and warrants immediate evaluation.
What healthy adaptation looks like
A reference point. Most patients show a clear adaptation curve across the protocol.
Sessions 1 to 5: ear pain risk is highest. Equalization technique is being learned. Fatigue is at maximum.
Sessions 6 to 15: ear technique is mastered. Fatigue starts to lessen. Some patients report energy gains.
Sessions 16 to 30: physical effects stabilize. Eye changes begin to develop in some patients. Clinical outcome measures (for FDA-cleared indications) start to appear.
Sessions 31 to 40: protocol completion. Eye changes peak. Re-evaluation of the indication is appropriate.
How to compare clinic safety practices
For broader HBOT safety context, see our safety guide. For oxygen-related harm specifically, see our oxygen-related harm explainer.
Reputable clinics screen for ear/sinus issues, monitor for adaptation, and have written protocols for managing side effects. Unaccredited clinics vary widely.
For more on choosing a clinic, see our clinic red flags guide and our UHMS accreditation explainer.
Bottom line
The most common HBOT side effects are mild and reversible. Ear pain affects 20 to 30% of patients but is usually manageable with technique. Post-session fatigue is common but resolves with adaptation, and eye changes are real but almost always reversible after the protocol ends.
Less common but reportable side effects (confinement anxiety, sinus pressure, mild peripheral symptoms) generally respond to clinic management. The serious adverse events (chamber fire, CNS oxygen harm, severe lung harm) are rare at UHMS-accredited centers.
For any HBOT decision, the side effect profile should be part of the calculation. The common side effects are inconvenient but rarely dangerous. The rare serious risks are real but manageable with proper clinic standards.
Related Reading
- HBOT side effects and safety: the real risk profile
- Oxygen toxicity in HBOT: real risks explained
- How to equalize your ears in a hyperbaric chamber
- HBOT and anxiety: how to manage claustrophobia
- UHMS-accredited HBOT facilities: what certification means
Frequently asked questions
How common is ear pain in HBOT?
Ear pain affects 20 to 30% of HBOT patients. Most cases are mild and resolve with equalization technique. Severe or persistent ear pain may indicate ear injury requiring ENT evaluation.
How long does HBOT fatigue last?
Post-session fatigue typically peaks 2 to 4 hours after the session and resolves within 12 to 24 hours. Most patients adapt by session 10. Persistent severe fatigue beyond session 15 should be discussed with the clinic.
Do HBOT vision changes go away?
Yes, in almost all cases. Temporary myopia is reversible and typically returns to baseline within weeks to months after the protocol ends. Full reversal can take up to 6 months.
Can HBOT cause permanent eye damage?
Permanent damage is rare. Cataract progression has been linked to long-term, high-session-count HBOT (above 150 to 200 sessions). Standard 40-session protocols carry minimal cataract risk.
When should I escalate side effects to my clinic?
Severe or persistent ear pain, sudden hearing loss, significant vision changes, seizure-warning symptoms (twitching, tunnel vision, anxiety during sessions), persistent severe fatigue beyond session 15, or chest pain and shortness of breath all warrant immediate clinical attention.
Medical disclaimer: This article is informational and does not constitute medical advice. HBOT carries real risks including ear injury, oxygen-related harm, and chamber fire. Discuss any HBOT plan with a doctor trained in hyperbaric medicine before starting. The FDA has cleared HBOT for 13 specific uses; uses outside that list are off-label.
-- The HBOT Finder Team