safety

What you should know before your session. Contraindications, side effects, and what the actual risks look like at 1.5 ATA.

Technical Plain English

Absolute Contraindications

Conditions where HBOT must not be administered regardless of pressure or protocol. Conditions where you should not use HBOT at all.

Untreated pneumothorax. Pressurization can convert a simple pneumothorax to tension pneumothorax during depressurization—a life-threatening emergency.
Untreated intraocular gas. Post-surgical SF₆ or C₃F₈ gas expands under pressure changes, risking retinal detachment or permanent vision loss. Wait three to six months post-surgery for full gas resorption.
Certain chemotherapy agents. Bleomycin causes fatal pulmonary toxicity potentiated by hyperoxia. Doxorubicin increases cardiotoxicity risk. Cisplatin and Disulfiram (which blocks superoxide dismutase) are also contraindicated. Get oncologist clearance before combining HBOT with any active or recent chemotherapy.

Collapsed lung (pneumothorax). Pressure changes in the chamber can make a collapsed lung much worse. Must be treated first.
Recent eye surgery with gas bubble. Some eye surgeries leave a gas bubble inside the eye that expands dangerously under pressure. Wait three to six months for it to absorb.
Certain chemo drugs. Some chemotherapy drugs (especially Bleomycin, Doxorubicin, and Cisplatin) interact badly with high oxygen. Get your oncologist's clearance.

Relative Contraindications

These require evaluation, not automatic exclusion. Many patients with these conditions use HBOT safely with appropriate monitoring. These need a conversation with your provider, but they don't automatically rule you out.

Active upper respiratory infection or sinusitis. Mucosal swelling impairs Eustachian tube equalization, increasing barotrauma risk. Delay until resolved.
Seizure disorders. Oxygen lowers seizure threshold. Incidence at clinical pressure (2.0–3.0 ATA, ppO₂ 2.0–3.0 atm): ~1 in 634 treatments. At 1.5 ATA with 93% O₂, ppO₂ is ~1.4 atm—below the ~1.6 atm CNS toxicity threshold.
COPD or emphysema. Bullae rupture risk under pressure changes. Imaging review recommended.
Pregnancy. Insufficient human data to establish safety. Animal studies haven't shown harm, but no one runs RCTs on pregnant women.
Implanted devices. Pacemakers, cochlear implants, and similar devices have pressure ratings. Most modern devices are rated well above 1.5 ATA. Check with manufacturer.
Severe claustrophobia. Manageable in many cases. Familiarization sessions and anxiolytics can help. Most patients habituate within three to five sessions.

Cold or sinus infection. Congestion makes it hard to equalize ear pressure. Wait until you're over it.
Seizure disorders. High oxygen can lower the seizure threshold. At 1.5 ATA, oxygen levels (~1.4 ppO₂) stay below the ~1.6 seizure threshold. Clinical incidence is ~1 in 634 at much higher pressures.
COPD or emphysema. Weakened lung tissue can be stressed by pressure changes. Get imaging reviewed first.
Pregnancy. Not enough human data. Probably fine, but no one's proven it.
Implanted devices. Pacemakers, cochlear implants, etc. Most modern ones handle 1.5 ATA easily. Check the manufacturer rating.
Severe claustrophobia. Familiarization sessions help. Most people adapt within three to five sessions.

Common Side Effects

Side Effect	Frequency	Details
Ear barotrauma	~2% of treatments	Middle ear barotrauma from Eustachian tube dysfunction during pressurization. Improves as equalization technique develops. Rare at 1.5 ATA versus higher pressures. Ear pressure or pain during pressurization, similar to flying. Gets easier with practice. Much milder at 1.5 ATA than higher pressures.
Claustrophobia	~25% initially	Anxiety response to enclosed space. Most patients habituate within three to five sessions. Feeling closed in. Most people adapt within three to five sessions.
Temporary myopia	Uncommon	Lens refractive index change from prolonged hyperoxia exposure. Fully reversible within weeks of stopping treatment. More common in extended protocols (>40 sessions at 2.0+ ATA). Mild nearsightedness that goes away within weeks after you stop. More common at higher pressures over many sessions.
Fatigue	Common early (sessions 1–35)	Expected component of the healing response. Immune upregulation and inflammatory clearance are metabolically expensive. Resolves as adaptive processes outpace inflammatory load. Your body is doing repair work and that takes energy. Normal during the first month or so. Clears up as you turn the corner around session 35.

Risk Profile at 1.5 ATA

Risk	At 1.5 ATA
Fire	Negligible. Chamber fills with normal air; concentrator delivers 93% O₂ only through the mask. Ambient O₂ in chamber stays near 21%. Negligible. The chamber is filled with normal air. Oxygen only goes through your mask.
O₂ toxicity seizure	Negligible. ppO₂ ~1.4 atm with concentrator at 1.5 ATA. Below the ~1.6 atm Paul Bert threshold for CNS toxicity. Negligible. The oxygen level at this pressure (~1.4 ppO₂) stays below the ~1.6 seizure threshold.
Barotrauma	Mild. Maximum 7 PSI (0.5 ATA gauge). Equivalent to 11 feet of seawater. Ear barotrauma possible; sinus and pulmonary extremely rare. Mild. 7 PSI max—like diving to 11 feet. Ear discomfort possible. Serious injury very rare.
Decompression	None. Below the threshold for nitrogen supersaturation at any treatment duration. None. 1.5 ATA is too low to cause decompression issues regardless of session length.
Pulmonary O₂ toxicity	Not at standard session lengths. Lorrain-Smith effect requires sustained high ppO₂ beyond what concentrator-based protocols produce. Not a factor at standard session lengths.

References

Adverse Effects

Yan, L. et al. "Adverse effects of hyperbaric oxygen therapy: a systematic review and meta-analysis." Front Med, 2023.

Seizure Incidence

Hazzard, B. et al. Seizure incidence approximately 1 in 634 treatments. PLoS One, 2025.

Yildiz, S. et al. Seizure incidence in 80,679 patient-treatments. Aviat Space Environ Med, 2004.

Fire Safety

FDA Safety Communication regarding hyperbaric oxygen therapy fire hazards. August 2025.

Not medical advice. Consult your physician before starting HBOT or any new therapy. Compiled from clinical literature, February 2026.