What Happens During a Hyperbaric Oxygen Therapy Session?

A hyperbaric oxygen therapy session takes about 60 to 90 minutes. You lie or sit inside a sealed chamber in comfortable cotton clothing while the air pressure is gradually raised, breathe oxygen through a mask or hood for the main part of the session, then the pressure is slowly returned to normal before you leave.

If you have never used a chamber before, the unfamiliar part is not the oxygen — it is the pressure change. Here is what the whole appointment actually involves, from what to wear to how you are likely to feel afterwards.

Before you arrive

Wear loose cotton clothing. Cotton is preferred over synthetic fabrics such as nylon, polyester or fleece because a pressurised, oxygen-rich environment changes how materials behave. Most clinics, ours included, will ask you to leave lighters, matches, vapes, battery-powered devices and loose electronics outside the chamber.

You will also usually be asked to skip hair products, aftershave, perfume and oil-based moisturisers on the day, since these are alcohol- or petroleum-based.

Eat something light beforehand. Arriving on a completely empty stomach is not ideal, but a heavy meal immediately before is uncomfortable once pressure is applied. A light meal an hour or two ahead works well. It is sensible to avoid fizzy drinks beforehand, and alcohol on the day.

If you have a cold, blocked sinuses or any congestion, tell the clinic before you travel. Equalising your ears is much harder when you are congested, and most clinics will simply rebook you.

What the chamber is actually doing

At normal sea level you breathe air that is roughly 21% oxygen at one atmosphere of pressure. A hyperbaric chamber raises the pressure around you above that level while you breathe oxygen at a much higher concentration.

Mechanically, that combination increases the amount of oxygen that dissolves directly into the plasma in your blood, rather than being carried only by red blood cells. That is the whole principle: more pressure plus more oxygen means more oxygen carried in solution. Chamber pressures vary by type — soft-shell chambers typically operate at milder pressures than rigid hard-shell chambers.

Inside the chamber: the three phases

1. Compression. The chamber is sealed and pressure rises gradually over roughly 10 to 15 minutes. This is the part people notice. Your ears will feel full, much like the descent of a flight. You clear them the same way — swallowing, yawning, or gently pinching your nose and blowing. Staff stay in contact with you throughout and will slow the rate down if you need more time.

2. The session itself. Once at pressure, you breathe oxygen and simply rest. Most people read, listen to something, message people, or sleep. You can talk to the operator at any point. This phase makes up the bulk of the appointment.

3. Decompression. Pressure is brought back to normal slowly over about 10 minutes. Ears usually clear themselves on the way back up. Then the chamber opens and you are done.

Afterwards

Most people walk out and carry on with their day — you can drive yourself home. Two things clients commonly report: feeling noticeably tired for a few hours afterwards, particularly after early sessions, and feeling thirsty. Drinking water afterwards is worth doing.

Some people notice temporary light-headedness or a brief popping sensation in the ears as things settle. If anything feels unusual, tell the clinic — that is what the post-session check is for.

Flying. If you have travel booked, mention it at your consultation. Both flying and hyperbaric sessions involve pressure changes, so the clinic will advise on spacing them sensibly around your trip.

How many sessions, and how often

This is the question that varies most between individuals, which is why it is settled at consultation rather than guessed from a website. Some people book a single session to see how they find it; others work through a course over several weeks, typically attending more than once a week.

Because of that, most clinics price sessions individually and in packages, with the per-session rate falling as the course length rises. You can see the full session lengths and package options on our hyperbaric oxygen therapy page, where single sessions are £75 until 30 November 2026 (usually £120) and longer courses bring the per session cost down to £55. See our full guide to HBOT costs.

Is it suitable for everyone?

No — and this is why a consultation comes first. There are circumstances in which hyperbaric sessions are not appropriate, and there are medications and recent procedures that need discussing beforehand. A proper consultation covers your history, your current medication, any ear or sinus issues, and what you are hoping to get out of it, before anything is booked.

If a provider is willing to put you in a chamber without asking any of that, treat it as a warning sign. Our guide to whether hyperbaric oxygen therapy is safe covers side effects and who should avoid it.

Frequently asked questions

What should I wear for hyperbaric oxygen therapy?

Wear loose, comfortable cotton clothing. Synthetic fabrics such as polyester, nylon and fleece are generally not permitted inside the chamber, and you will be asked to remove lighters, vapes, electronic devices and loose jewellery. Skip perfume, aftershave, hair products and oil-based moisturisers on the day of your session.

Can you eat before hyperbaric oxygen therapy?

Yes, and a light meal an hour or two beforehand is preferable to arriving hungry. Avoid a heavy meal immediately before, since pressure makes that uncomfortable, and skip fizzy drinks and alcohol on the day. Bring water for afterwards — most people are thirsty once the session ends.

How long does a hyperbaric oxygen therapy session take?

Allow 60 to 90 minutes in the chamber, plus time either side for checks. That total includes roughly 10 to 15 minutes of gradual compression at the start and about 10 minutes of decompression at the end, with the main oxygen-breathing phase in between. Session lengths differ by clinic.

How many sessions do you need?

It depends entirely on the individual, which is why it is decided at consultation. Some people book a single session; others work through a course over several weeks, often attending more than once a week. Clinics price both ways, and the per-session cost usually falls as the course gets longer.

Can you fly after hyperbaric oxygen therapy?

Raise your travel plans at consultation before booking. Flying and hyperbaric sessions both involve changes in pressure, so a clinic will advise on how to space them around your trip. This matters most if you are flying within a day or so of a session, or sitting a course close to travel.

Does hyperbaric oxygen therapy make you tired?

Feeling tired for a few hours afterwards is one of the things clients report most often, particularly after their first few sessions. It usually settles as people get used to the routine. Drinking water afterwards helps. Anything beyond ordinary tiredness is worth mentioning to the clinic.

What should you not do before a session?

Do not drink alcohol on the day, do not arrive congested with a cold or blocked sinuses, and do not apply perfume, aftershave, hair product or oil-based moisturiser. Leave lighters, vapes and battery-powered devices outside the chamber. Tell staff about any recent ear or sinus problems before you are sealed in.

Is mild hyperbaric therapy the same as a hard-shell chamber?

No — the difference is pressure. Soft-shell chambers operate at milder pressures than rigid hard-shell chambers, so the two are not interchangeable, and session protocols differ between them. Ask any provider which chamber type they run and at what pressure before you book.