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HBOT side effects and safety: what to know before your first session
Ear pressure is the most common side effect of hyperbaric oxygen therapy, and most side effects are mild. The serious ones are rare, and good screening is what keeps them that way.
Hyperbaric oxygen therapy is generally well tolerated when patients are properly screened and supervised. Safe is not the same as risk-free, though, and you deserve a clear picture of what can happen before your first session.
Is HBOT safe?
A 2017 review of HBOT side effects in Advances in Wound Care described hyperbaric oxygen as among the safest therapies in use today. The same review makes the point that side effects still need to be understood, explained and prevented, because most of them are predictable.
Side effects of HBOT come from two things: pressure, which affects air-filled spaces such as the ears, sinuses and lungs, and oxygen, which in high doses can affect the brain, lungs and eyes. Screening before treatment targets both.
Serious side effects are rare, and screening, pressure selection and supervision exist to keep them rare.
Common side effects, usually mild
Ear pressure (middle ear barotrauma)
This is the most common side effect of HBOT. As the chamber pressurises, pressure builds on the eardrum, much like during a flight descent. If the small tube linking the middle ear to the back of the nose does not open in time, you feel fullness or discomfort, and occasionally pain or bruising of the eardrum.
Reported rates vary widely between studies, largely depending on how closely ears are examined after each session. Most cases are mild. Equalising early and often, and telling the team straight away if you cannot clear your ears, keeps it to a minimum.
Sinus pressure
Blocked sinuses cannot equalise easily. Far more likely with a cold, allergies or a blocked nose, when the session is usually postponed.
Temporary short sight
Distance vision can blur slightly after many sessions, typically around 20. It usually settles over weeks to months after the course. Avoid changing glasses mid-course.
Tiredness
Some people feel tired or light-headed after a session. This is usually short-lived.
Some people also feel uneasy in an enclosed space. At Aquila you sit upright in a rigid, transparent chamber, you can talk to the team throughout, and a partner or friend can share the session. Tell us beforehand if confined spaces worry you.
Rare but serious side effects
| Side effect | What it is | How the risk is reduced |
|---|---|---|
| Oxygen toxicity seizure | A seizure caused by breathing high-pressure oxygen. Published series report roughly 1 in 2,000 to 1 in 10,000 treatments, and the risk rises with higher pressure and with fever. | Screening for seizure history, fever and relevant medicines, choosing an appropriate pressure and monitoring throughout. It stops when oxygen is removed. |
| Low blood sugar | People with diabetes on insulin or some tablets can see their blood sugar fall during a session. | Telling us about diabetes treatment, eating normally beforehand and checking blood sugar before the session. |
| Lung injury from pressure | Very rare. Air trapped in the lungs can expand as pressure falls. | Screening for lung conditions. An untreated collapsed lung (pneumothorax) rules out HBOT completely. |
| Fire | An oxygen-rich environment makes materials burn more easily. | Strict rules on clothing, electronics, lighters and certain skin and hair products inside the chamber. |
Who needs extra assessment before HBOT
An untreated pneumothorax (collapsed lung) is the one absolute reason not to have HBOT. The following need a doctor's review first, and may mean postponing, adjusting or not proceeding:
- Lung conditions, such as COPD, emphysema or a previous collapsed lung
- Ear or sinus problems, recent ear surgery or a perforated eardrum
- A cold, blocked nose, cough or fever on the day
- A history of seizures
- Diabetes treated with insulin or tablets that can cause low blood sugar
- Certain chemotherapy drugs, current or past, and some other medicines
- Pregnancy
- Pacemakers and other implanted or wearable medical devices
- Severe anxiety in enclosed spaces
New cough, cold, fever or ear pain, a change in medicines, low blood sugar, or any unusual symptom after your last session.
How we reduce risk at Aquila
- Doctor-led screening of your medical history, medicines, ears, sinuses and lungs before your first session
- Equalisation coaching before you start, and gradual pressurisation
- Pressure matched to your goal: our upright hard-shell chamber operates at up to 2.0 ATA, set at your clinical assessment rather than by default. What ATA means
- Monitoring throughout, with the team able to talk to you and pause at any point
- Safety checks before every session, including clothing and items brought into the chamber
HBOT at Aquila Medical Center
Read more about Hyperbaric Oxygen Therapy in Singapore, including chamber details, fees, indications and what to expect, or about HBOT for sudden hearing loss, where ear checks matter most.
When to tell the team immediately
During or after a session, speak up at once if you have ear pain you cannot clear, chest pain, shortness of breath, twitching, changes in your vision, or you simply feel unwell. The team can stop pressurising or bring the pressure down.
Questions patients ask
Is HBOT safe?
For most people, yes, when it is properly screened and supervised. Most side effects are mild and short-lived. Serious side effects are rare.
Can HBOT damage my ears?
Ear pressure is the most common side effect, and occasionally the eardrum is bruised. Equalising early, going slowly and stopping if you cannot clear your ears keeps this to a minimum. Tell us about any previous ear problems.
Can I have HBOT with a cold?
Usually not on that day. A blocked nose makes it hard to equalise your ears and sinuses, so the session is normally rescheduled.
Does HBOT affect eyesight?
Some people notice slightly blurred distance vision after many sessions. It usually returns to normal over weeks to months after the course ends.
Is HBOT safe in pregnancy?
Pregnancy needs an individual medical review. Elective HBOT is generally not started during pregnancy without a clear medical reason.
Selected references
- Heyboer M, Sharma D, Santiago W, McCulloch N. Hyperbaric Oxygen Therapy: Side Effects Defined and Quantified. Advances in Wound Care. 2017;6(6):210–224. PubMed.
- Plafki C, Peters P, Almeling M, Welslau W, Busch R. Complications and side effects of hyperbaric oxygen therapy. Aviation, Space, and Environmental Medicine. 2000;71(2):119–124.
- Undersea and Hyperbaric Medical Society. Hyperbaric Oxygen Therapy indications and clinical resources. UHMS.
This article is educational and does not replace individual medical assessment. Suitability for HBOT, pressure and session length depend on the indication, patient factors and supervising clinician. Content reviewed by Dr Stephen Chu, Medical Director, Aquila Medical Center, Singapore. Last reviewed: 24 September 2026.
Considering HBOT in Singapore?
Every course at Aquila starts with a doctor-led assessment of whether HBOT is suitable and safe for you.