HBOT Side Effects and Safety: What Can Go Wrong and How Often

Hyperbaric oxygen therapy's most common side effect is ear discomfort during pressure changes, and its most serious risks are rare and largely preventable by screening. That is the accurate summary, and the detail underneath it is worth reading if you are considering a course.

The common side effects

Ear and sinus pressure (very common). As the chamber pressurises, the air in your middle ear compresses and the eardrum pulls inward until you equalise. It feels exactly like an aircraft descending. You clear it by swallowing, yawning, or pinching your nose and gently blowing. If you cannot clear it, you tell the operator and they slow or pause the descent.

Middle ear barotrauma; where the pressure difference causes actual irritation or fluid behind the eardrum; is the single most frequent complication of HBOT. It is nearly always mild and self-resolving, and it is largely avoidable: pressurise slowly, learn the technique properly, and never dive with a cold or blocked sinuses.

Tiredness afterwards (common). Many people feel flat or sleepy for a few hours after a session. It passes and is not a warning sign.

Temporary short-sightedness (common on long courses). High-dose oxygen changes the shape and refractive index of the lens. Over 20 or more sessions, distance vision can blur; people notice it driving. It reverses, typically over weeks to a few months after the course ends. If you have cataracts already, they may progress faster, which is a conversation to have before starting rather than during.

Claustrophobia (variable). A monoplace chamber is transparent and you can see out and talk to staff throughout, which is enough for most people with mild claustrophobia. If enclosed spaces are a genuine problem for you, say so before you book, not on the day.

The rare but serious ones

Oxygen toxicity seizure. High-dose oxygen at pressure can, uncommonly, provoke a seizure. Risk rises with pressure and session length, which is one reason wellness protocols run at the lower end of the pressure range. Air breaks; short periods breathing normal air mid-session; reduce it further. The seizure itself is not damaging; the management is to reduce oxygen and it stops.

Pulmonary barotrauma. If air is trapped in the lung and cannot escape as pressure drops, it expands. This is why untreated pneumothorax is an absolute contraindication and why lung conditions that trap air need specialist assessment. In screened patients this is rare.

Confinement anxiety severe enough to abort a session. Not dangerous, but worth naming: the session can be stopped, and it is stopped slowly rather than instantly, because rapid decompression carries its own risks.

Who should not have hyperbaric oxygen therapy

That table is the reason screening exists. None of it is exotic; it is a medical history and a conversation; but it is the difference between hyperbaric oxygen as a medical treatment and hyperbaric oxygen as an unsupervised consumer product.

The fire question

Oxygen does not burn, but it makes everything else burn far more readily. Hyperbaric chambers are run with that in mind: cotton clothing only, no oils, lotions, hair products, aerosols or synthetic fabrics, no electronics, no lighters. It can feel excessive at the door. It is not; chamber fires are the mechanism behind essentially every catastrophic hyperbaric incident on record, and every one of those precautions traces back to a specific historic event.

A clinic that is relaxed about this is a clinic to leave.

What "safe" actually depends on

Three things, in order:

1. Screening before the first session. A real medical history, checked against the contraindications above, by someone qualified to interpret it.
2. Supervision during. Someone monitoring, able to slow the descent, call an air break, or abort.
3. Appropriate pressure and dose. Higher is not better. Wellness and recovery protocols sit at the lower end of the clinical range for good reason.

Home and studio soft chambers typically have none of the first two. They run at low pressure, which reduces some risks, but the absence of screening is the part that should give you pause; the contraindications do not disappear because the pressure is lower.

If you're considering HBOT because you're exhausted

Worth a moment before booking a course.

Hyperbaric oxygen raises how much oxygen dissolves in your blood plasma. It does not address why your blood was under-delivering oxygen in the first place. If the answer to that is iron deficiency; common in the UK, particularly in women with heavy periods, in pregnancy, and after surgery; then you are treating a downstream symptom while the cause continues.

Low iron means less haemoglobin, and less haemoglobin means less oxygen carried, no matter how much you breathe. It is diagnosed with a ferritin blood test and it is treatable. That is a much cheaper thing to rule out first.

The bottom line

For a screened, supervised patient, hyperbaric oxygen therapy is a well-tolerated treatment whose commonest side effect is a blocked-ear sensation you already know from flying. The serious risks are real but uncommon, and nearly all of them are managed by the medical history taken before you ever enter the chamber.

The safety question is therefore less "is HBOT safe" and more "is this provider screening me". Ask.

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Related reading: HBOT benefits: what the evidence shows · What is a hyperbaric chamber? · What is hyperbaric oxygen therapy? · Does the NHS offer HBOT?

In Wales: Hyperbaric oxygen therapy in Cardiff · HBOT across Wales