The short answer: HBOT is generally considered safe (Mayo Clinic). The most common side effects are ear pressure and sinus discomfort during pressurization. Serious complications are rare. Key contraindications include untreated pneumothorax, certain lung conditions, and some medications. Proper pre-session screening is essential.
Most HBOT marketing talks about outcomes. Serious HBOT education also talks about fit. That does not mean hyperbaric oxygen therapy is unusually dangerous. Mayo Clinic describes it as generally safe, with most complications mild and serious complications rare. But “generally safe” is not the same as “good for literally everyone on demand.” Pressure changes, oxygen exposure, medical history, and the details of the chamber environment all matter, especially when someone has lung disease, ear problems, recent surgery, fever, claustrophobia, or a medication profile that deserves a closer look.
The practical question is not whether side effects exist. Every real therapy has side effects. The question is whether the facility knows how to screen for them, explain them, and respond when they show up. In our experience, the strongest operators are not the ones who hand-wave risk away. They are the ones who make clients feel informed enough that the session is calm rather than mysterious.
Educational note: this article is not personal medical advice. It is a screening and expectations guide. People with chronic conditions, recent procedures, or complicated medication histories should clear HBOT with the right clinician before treatment.
The most common side effects people should expect
Ear and sinus pressure are the usual complaints for a reason
The side effect most people notice first is ear pressure. Johns Hopkins notes that as chamber pressure rises, it is common to feel ear pain or a popping sensation, and Mayo Clinic lists ear pain, middle-ear injury, and sinus pressure among the most common complications tied to increased pressure. None of that means HBOT is inherently unsafe. It means pressure has to be managed with respect. The ears and sinuses are where poor equalization shows up first, which is why a mild cold, congestion, allergies, or recent ear trouble can turn an otherwise normal session into an uncomfortable one.
In practice, this is the side-effect category good operators handle best because it is predictable. They coach equalization, they slow compression when needed, and they do not treat “push through it” as a badge of honor. If a center does not ask whether you are congested, whether you recently had ear surgery, or whether you have a history of pressure problems, that is a red flag. For a more detailed play-by-play of how ear pressure shows up in real time, read what happens during your first HBOT session.
Fatigue, lightheadedness, glucose swings, and vision changes are real too
Ear pressure gets the attention, but it is not the whole picture. Johns Hopkins notes that people may experience fatigue or lightheadedness after HBOT, while Mayo Clinic lists short-term changes in sight, temporary decline in lung function, and low blood sugar in people with insulin-treated diabetes among possible complications. Repeated treatment courses can also be associated with temporary nearsightedness in some people. Most of these issues are manageable when they are anticipated. They become more of a problem when they surprise people.
That is why pre-session communication matters. Someone with diabetes may need glucose monitored more carefully. Someone who is already anxious in enclosed spaces may do better with extra coaching or, in some cases, medication prescribed by a clinician. Someone with a long treatment plan should know that transient visual changes are a recognized possibility. A good facility does not dump that information on people to scare them. It explains it so the experience feels controlled, not unpredictable.
| Side effect or complication | How common it is in practice | Why it happens | What a good operator does |
|---|---|---|---|
| Ear fullness, popping, or pain | Very common | Pressure changes during compression and decompression | Coaches equalization, slows the rate, pauses if needed |
| Sinus discomfort or nose symptoms | Common when congested | Pressure changes in already irritated sinuses | Screens for colds, allergies, or fever before treatment |
| Fatigue or lightheadedness | Usually mild | Post-session response can vary from person to person | Checks how you feel before you leave and advises normal recovery |
| Temporary vision changes | Less common, more relevant with repeated sessions | Oxygen and pressure exposure over a course of treatment | Explains possibility up front during longer treatment plans |
| Low blood sugar in insulin-treated diabetes | Specific to at-risk patients | Glucose handling can change during treatment | Coordinates timing, screening, and glucose awareness |
| Oxygen toxicity seizure or lung complications | Rare but serious | Excess oxygen exposure or vulnerable lung status | Screens carefully and follows protocol limits |
Contraindications and cautions that deserve real attention
The one absolute contraindication is untreated pneumothorax
If you want the cleanest non-negotiable in HBOT screening, this is it. StatPearls states that the only absolute contraindication to HBOT is an untreated pneumothorax. The reason is straightforward and serious: changing ambient pressure in someone with trapped air around the lung can precipitate a life-threatening tension pneumothorax during ascent. That is not a wellness gray zone. It is a hard stop until the issue is appropriately evaluated and managed.
For clients, the practical takeaway is simple: do not self-clear chest symptoms or prior lung events because you “feel okay today.” For operators, the takeaway is equally clear: a chamber booking is not the place to improvise around lung history. If someone has a known collapsed lung, suspected pneumothorax, or an unresolved thoracic issue, the conversation belongs with medical professionals before it belongs in a chamber.
Relative cautions are not always a “no,” but they are never a shrug
The rest of HBOT screening lives in the category of relative contraindications and caution flags. That group includes certain lung diseases, upper respiratory infections, fever, recent ear surgery or injury, claustrophobia, insulin-treated diabetes, eye surgery involving trapped gas, and specific medications that can interact badly with oxygen exposure. StatPearls also notes caution with drugs such as doxorubicin, bleomycin, disulfiram, cisplatin, and mafenide, while Johns Hopkins warns that recent ear surgery, cold symptoms, or some lung conditions can increase risk. These are not all automatic deal-breakers. They are signals to slow down and ask better questions.
This is where good screening can save everyone time. Someone with mild claustrophobia may still do perfectly well with coaching and a chamber design that feels less confining. Someone with a stuffed-up nose on the day of treatment may simply need to reschedule. Someone with diabetes may need timing and monitoring adjustments. Relative contraindications are best understood as decision points, not as marketing inconveniences. The right question is not “Can we still sell the session?” It is “What makes this person safer and better informed?”
| Issue to screen for | Why it matters in HBOT | Typical next step | Absolute stop or clinician conversation? |
|---|---|---|---|
| Untreated pneumothorax | Pressure change can turn it into a life-threatening emergency | No chamber exposure until resolved | Absolute stop |
| Cold, fever, sinus congestion, or allergies | Harder to equalize ears and sinuses | Delay or medically guide treatment | Clinician conversation |
| Recent ear surgery or ear injury | Pressure may worsen injury or pain | Clear with treating physician first | Clinician conversation |
| Certain lung diseases or prior lung collapse | Pressure changes can raise complication risk | Review pulmonary history carefully | Clinician conversation |
| Insulin-treated diabetes | Low blood sugar risk during treatment | Plan timing and glucose monitoring | Clinician conversation |
| Claustrophobia or severe anxiety | Enclosed chamber may be poorly tolerated | Extra coaching, alternative setup, or medical support | Clinician conversation |
| Specific medications | Some drugs increase risk under HBOT | Medication review before treatment | Clinician conversation |
What safe operators do differently
Good screening and fire-safety discipline are part of treatment quality
Screening is only half the story. The chamber environment itself matters too. In August 2025, the FDA issued a letter to healthcare providers after serious injuries and deaths linked to hyperbaric oxygen therapy devices and reminded facilities to follow manufacturer instructions, maintain equipment, train staff, monitor patients, and rigorously enforce fire-prevention protocols. That includes controlling what people wear or bring into the chamber and paying attention to static-generating materials. None of that is glamorous, but it is part of what separates a serious program from a casual one.
The important mindset shift is this: safety is not a separate add-on to treatment quality. It is treatment quality. If you are evaluating a facility or buying equipment for your own business, ask about staff training, chamber maintenance, patient monitoring, communication systems, and prohibited items. Then compare those answers with what you see on the floor. If you are looking at systems now, explore the chamber and then read our guide to hard-shell vs soft-shell hyperbaric chambers so you are comparing chamber types with the right questions in mind.
What to do if symptoms show up during a session
The safest time to report discomfort is the moment it starts, not after you decide to “see if it passes.” Ear pain, chest discomfort, unusual shortness of breath, severe anxiety, or symptoms that feel out of proportion to a normal first-time session should be reported immediately. Chambers can be paused, decompression can be adjusted, and staff can decide whether the session needs to stop. Johns Hopkins also notes that short air breaks may be used during treatment to reduce the risk of tissues taking in too much oxygen.
That same rule applies after the session. If your ears feel significantly worse later, if you are having persistent sinus pain, or if anything about the experience felt off, tell the provider before session two. Good centers do not get defensive about symptom reporting. They treat it as useful data. If you want to talk through those questions with a human before booking or buying, you can contact the team or read more about Superhuman and how operator experience shapes chamber education.
Final thoughts
HBOT side effects are real, but the most common ones are also predictable. Ear pressure, sinus discomfort, fatigue, temporary visual changes, and glucose issues in the right patient population should be part of the normal conversation, not something discovered by accident. The one hard line is untreated pneumothorax. Most other cautions live in the category of “ask, screen, and plan properly.”
The easiest way to lower risk is to choose serious operators, ask better pre-session questions, and never treat discomfort as something you should quietly endure. For related reading, start with what happens during your first HBOT session, how many HBOT sessions people usually need, and our guide to HBOT for inflammation if your interest is driven by chronic recovery rather than a specific medical indication.