Hyperbaric oxygen therapy side effects: how common are they?

Hyperbaric oxygen therapy side effects fall into two groups: injuries caused by the pressure change, and effects caused by breathing very high concentrations of oxygen. Hyperbaric oxygen therapy means breathing oxygen inside a sealed chamber pressurised above normal air pressure, given as a course of daily sessions rather than one visit - 30 to 40 sessions of 80 to 90 minutes in one trial for radiation damage to the bladder [14].

The ears take most of it. A review of 54 studies covering 18,284 patients found 15% had an ear problem, about one in seven [2]. Most cases were minor: of the middle ear barotrauma (pressure injury to the eardrum and the air space behind it) that occurred, 42.8% was graded mild and 6.4% severe [2]. An earlier review of the field put ear barotrauma at up to 2% of treated patients [7], so the reported rate depends heavily on how closely anyone is looking for it.

Vision changes are the other frequent one, and they usually reverse. Among 1,005 breast cancer patients treated for radiation damage with at least 20 sessions, 57.3% developed some degree of myopia - myopia being short-sightedness, where distant objects blur - and 17.8% had mild ear barotrauma [8]. A Cochrane review of hyperbaric oxygen for radiation injury found patients given the therapy were about four times as likely to lose some sharpness of vision as those who were not, called that finding high-certainty, and noted the change is usually temporary [1]. In a separate two-year trial in 50 people with diabetes and foot ulcers, sharpness of vision did not change at all, and neither did damage to the retina at the back of the eye [12].

The serious ones are rare. In that same group of 1,005 patients, 3.2% had a side effect rated moderate or severe [8]. Seizures triggered by oxygen happen at the higher chamber pressures and mostly during emergency treatment rather than a planned course [7]. Breathlessness with a cough and pain on breathing in sits among the rarer oxygen effects, and claustrophobia inside the chamber is common enough that staff handle it with reassurance and coaching [7].

Some people meet ear trouble more than others. The 54-study review found the risk was higher with [2]:

• older age
• female sex
• head and neck conditions
• nerve damage affecting sensation
• difficulty clearing the ears before treatment started

The one thing that protected people was being taught how to equalise ear pressure properly [2]. There is also a clue about the cause: in trials where the comparison group was pressurised too, ear injury was no more common in the oxygen group, while in trials where the comparison group stayed at normal pressure it was many times more common [1]. That points at the pressure change rather than the oxygen as what hurts the ear.

Two forces do the work inside a hyperbaric chamber, and the same two produce the side effects: raised pressure and raised oxygen [10].

Pressure is the blunt one. Any air-filled space in the body shrinks as the pressure around it rises, which puts the middle ear, the sinuses and the lungs first in line [9]. The middle ear equalises through a narrow tube running to the back of the throat, and when that tube does not open in time the eardrum takes the strain. It is why chambers are pressurised slowly and why staff teach swallowing, yawning and gentle nose-blowing before the first session [2].

Oxygen works more slowly. Chambers deliver pure oxygen well above normal air pressure, 240 to 250 kilopascals in one trial, roughly two and a half times the pressure at sea level [14]. That forces far more oxygen into the blood and tissue than the body ever meets at the surface. The benefits are thought to come from that oxygen load and from the controlled oxidative stress it creates, meaning chemical wear from reactive oxygen molecules that doubles as a signal to tissue [10]. The same chemistry, repeated across a course, is what produces the gradual short-sightedness that usually reverses once the sessions stop, and the cough and chest discomfort seen more rarely [7].

Nearly every number here comes from patients treated in hospital chambers for approved medical conditions - radiation damage after cancer treatment and non-healing diabetic foot ulcers - on courses of 20 to 60 sessions [1][8][14][15]. None of it measures what happens to a healthy person buying a handful of sessions, and none of these studies tested the low-pressure inflatable chambers sold for home and wellness use.

The populations are narrow. The 57.3% myopia figure comes entirely from breast cancer patients being treated for radiation damage [8], and the eye study that found nothing followed 50 people with diabetes and foot ulcers, median age 67 [12]. Neither group resembles a healthy 45-year-old walking into a clinic.

The rates also disagree with each other: ear injury appears as up to 2% in one review [7] and 15% across 18,284 patients in another [2]. That is what happens when studies define a side effect differently and look for it with different effort, rather than a sign that one of them is wrong.

The record has two holes:

• Long-term safety is thinly tracked. The five-year trial in people with bladder damage from radiotherapy recorded side effects only while patients were actually receiving treatment [14].
• Serious events are counted inconsistently. A 2025 meta-analysis of diabetic foot ulcer trials found hyperbaric oxygen lowered the risk of major amputation while carrying a higher rate of serious side effects [5].

Longevity clinics list hyperbaric oxygen alongside services such as IV drips and biological age testing, and a first visit is usually a screening conversation rather than a session in the chamber. Staff ask about ear and sinus trouble, recent colds, chest conditions and previous surgery, because those are what make a pressure change painful or unsafe, and they teach the equalising technique that the research ties to fewer ear injuries [2]. Chamber time is sold in courses rather than single visits, and the trials behind these safety numbers ran 20 to 60 sessions of 80 to 90 minutes [8][14][15]. Worth asking before signing up: what pressure the chamber runs at, how many sessions are being proposed, and what happens if your ears will not equalise on day one.