What is hyperbaric oxygen treatment (HBO)?

Hyperbaric oxygen treatment (HBO) involves giving the body extra oxygen. 'Hyper' means increased and 'baric' relates to pressure. Oxygen is one of the gases in the air and we need it to live. Normally, oxygen makes up just over one fifth (21%) of the air.

In HBO treatment, people breathe in pure (100%) oxygen under increased pressure. You sit or lie in a chamber that controls the pressure. It is called a hyperbaric oxygen chamber. You breathe in oxygen using a mask over your nose and mouth, or a clear hood.

How HBO treatment works

Oxygen is carried around the body by the blood. HBO gives the blood extra oxygen. The extra oxygen can help wounds to heal if:

  • infection is affecting healing
  • tissue damage is making it difficult for the blood to reach the area.

HBO treatment:

  • increases oxygen levels in areas where they are low because of illness or injury
  • encourages new blood vessels to grow so that they can carry more oxygen and nutrients to the tissues
  • increases the ability of white blood cells to kill bacteria and prevent infection
  • reduces any swelling, pressure and pain that may happen around the wound.

When HBO treatment can be used

HBO treatment can help when body tissues have low oxygen levels.

People with cancer may have HBO treatment for:

In general, it can be used to treat:

  • an illness caused by diving (the bends)
  • wounds or infections that are difficult to treat.

Researchers are looking at other uses for HBO treatment.

HBO treatment is not always available on the NHS. If you have it, the treatment centre may ask your permission to collect information about you. This may include information about your symptoms and the effect of the treatment.

HBO treatment for radiotherapy side effects

Radiotherapy can cause changes in the oxygen supply to tissues in the treated area. This is because radiotherapy affects normal cells and blood vessels, as well as cancer cells.

The small blood vessels in the treated area can be damaged by radiotherapy. This can reduce the amount of blood supplied to that area. This makes it more difficult for oxygen and nutrients to reach the tissues.

Over time, the affected tissues may become weaker and break down (ulcerate). Rarely, some tissues may die completely (radiation necrosis). These radiation injuries can happen slowly, over months or years.

HBO treatment increases the oxygen supply to damaged tissue. This encourages new blood vessels to grow and the tissues to heal.

Research has shown that HBO treatment may help with the following side effects of radiotherapy.

Chronic radiation cystitis

Radiotherapy is used to treat some types of cancer in the pelvis. The pelvis is the area between the hips. The bladder is in the pelvis. This means radiotherapy to this area can sometimes cause long-term inflammation of the bladder (chronic cystitis). Symptoms include:

  • needing to pass urine (pee) more often
  • pain when passing urine
  • difficulty passing urine
  • blood in the urine (haematuria).

These problems can happen months or years after treatment.

HBO treatment may help to improve these symptoms. It may be used when other treatments have not worked.


Radiotherapy is often used for cancers in the head and neck.

The tissues around this area are easily damaged. Having surgery before radiotherapy can increase the risk of damage. Rarely, an area of bone is affected and starts to break down and die. Doctors call this osteoradionecrosis, or ORN. Bone damage can also happen when radiotherapy is given to other areas of the body, such as the chest or pelvis.

You may have HBO treatment after radiotherapy for a head and neck cancer. The aim is to help prevent damage to the jaw bone.

If the bones have already been damaged, treatment for ORN includes:

  • antibiotics
  • washing out the area with salt water (saline irrigation).

Sometimes, you have surgery to remove some, or all, of the affected bone.

HBO treatment can help tissues around the area of ORN to heal by encouraging blood vessels to grow. But, HBO treatment cannot restore the dead bone. So sometimes surgery is needed after HBO to remove the affected bone.

HBO treatment can also be given before and after reconstructive surgery to:

  • help healing
  • prevent infection
  • encourage blood vessels to grow and form new bone.

If wounds or tissue are infected, you usually have drugs or surgery as well as HBO treatment.

Tooth removal

Having a tooth removed shortly before, during, or after radiotherapy to the mouth and jaw area may increase the risk of ORN. This is because of the reduced oxygen supply to the healing area.

HBO treatment can be given to help prevent ORN. It should be given before and after the tooth is removed, to help the healing process.

Chronic radiation effects on the bowel

Radiotherapy to treat cancers in the pelvis can affect the bowel. The bowel is very sensitive and rarely, radiation damage can cause long-term symptoms. These include:

  • pain
  • bleeding
  • changes in how the bowel works.

HBO treatment may help improve these symptoms when other treatments have not worked.

HBO treatment for skin grafts or flaps

When surgeons are removing a cancer, they sometimes need to remove a large area of skin. They may then create skin grafts or a skin flap. For example, this could happen during surgery for skin cancer, including melanoma, or some types of sarcoma.

To create a skin graft, surgeons take a layer of skin from a different part of the body. They use this to cover the area where the cancer was removed from.

A skin flap is a thicker layer of skin that is taken from an area close to where the cancer was removed. Surgeons can cut the skin but leave it partly connected, so it has a blood supply. They can then move the skin to cover the wound and stitch it in place.

Sometimes there can be problems with skin grafts or flaps healing. Using HBO treatment to give more oxygen to the area may help.

How HBO treatment is given

You will need to be referred to a centre that gives HBO treatment. Your specialist can tell you if they think it might be helpful.

The British Hyperbaric Association lists some of the UK centres that use HBO treatment. Your doctor should be able to tell you where your nearest treatment centre is. You may have to travel for treatment. Speak to your hospital doctor or nurse if you need help with transport. This may be available in some areas.

Before having HBO treatment, you see a doctor. They make sure you are well enough for treatment. You have HBO treatment inside a chamber. Tell the doctor or nurse if you have a fear of enclosed spaces (claustrophobia). The nurse can give you support, such as help with relaxation techniques to calm you.

Treatments are usually repeated over days or weeks. You should complete the whole course for the most benefit. Your treatment session may be delayed if you feel unwell or have:

  • a severe cold or flu
  • a chest infection
  • a runny nose
  • sickness (nausea).

This is because HBO treatment can make some side effects worse. You should tell your nurse or doctor if you have any of these symptoms before starting a treatment session. You may want to phone the HBO treatment centre to discuss this before travelling.

If you smoke, you will be asked to stop smoking before and during treatment. This is because smoking can reduce the level of oxygen in your body.

The high level of oxygen in the HBO chamber increases the risk of fire. To reduce this risk, the staff give you cotton clothes to wear in the chamber. You are not allowed to take certain items into the chamber, including mobile phones and watches.

It is usually best to go to the toilet before your treatment, although some chambers have toilets. Talk to the nurse if you are worried about needing the toilet during your treatment.

Treatment is usually painless. The chamber has windows so you can see out and staff can see you. There are two types of chamber:

  • a monoplace chamber
  • a multiplace chamber.

Some treatment centres have both types, and some only have one.

Monoplace chambers

These treat one person at a time. You lie on a padded stretcher that slides into a clear plastic tube (chamber) that is about 60cm (2ft) wide.

Monoplace chmabers

Multiplace chambers

These can treat more than one person at a time, and are more common than monoplace chambers. Some can treat up to 12 people at a time. These chambers are quite large, and you will be able to walk around inside. There are staff inside and outside the chamber during your treatment. You usually sit inside the chamber but it may be possible for you to lie down if this is needed for your treatment.


Multiplace chambers

Compression phase

When you are inside the chamber, the doors are closed. Air is blown into the chamber to increase the pressure. You will hear a hissing sound. The chamber will feel warmer.

You will need to clear your ears as the pressure begins to increase. A nurse or doctor will show you how to do this. Clearing your ears helps to balance the pressure in them and prevent pain in your eardrum. It is a similar feeling to when you take off or land in a plane, or travel on a train through a tunnel.

Treatment phase

When the pressure reaches the correct level, staff ask you to put on a mask or a clear hood. The mask covers your nose and mouth. This delivers pure (100%) oxygen.

Treatment mask 

Monoplace chambers are pressurised with 100% oxygen, so you might not need to wear a mask or hood.

During treatment you will be able to read, listen to music or watch TV (if the chamber has one). You can see and talk to a member of staff during the treatment.

The length of each treatment depends on what you are being treated for. It can last from 60 to 90 minutes at a time.

Decompression phase

Near the end of the treatment, the pressure in the chamber is slowly lowered. You may feel your ears popping. As the chamber decompresses, it will start to feel cooler. After the decompression phase you can leave the chamber.

Possible side effects of HBO treatment

HBO treatment is very safe and does not cause many side effects. They are usually minor and do not last long. If you think you may have other side effects, speak to your nurse or doctor at the treatment centre.

Blurred vision

This can happen after several treatments. HBO treatment can cause temporary short sightedness (myopia). This usually develops gradually and then gets better slowly when treatment ends. Using glasses or changing your prescription for a short time may help. But blurred vision usually only lasts a few weeks.

Feeling light-headed

Some people feel light-headed after treatment. This only lasts for a few minutes.


You are more likely to feel tired if you have more than one session of HBO treatment in a day. The effect usually wears off a few days after the treatment sessions are finished.

Ear problems

Rarely, the change in air pressure can damage the eardrum. Before treatment, a nurse or doctor will show you how to balance the pressure in your ears. This can help prevent ear problems.

Less common side effects

Painful sinuses

The change in pressure may cause discomfort if you have congested sinuses. This can cause headaches or facial pain. Decongestant medicine can help control this. But sometimes the session of HBO treatment needs to be stopped.

Effects on the lungs

Very rarely, HBO treatment can affect the lungs. This usually only happens if HBO treatment is given over a long period of time. It is rare if you have had HBO treatment to help with the effects of cancer treatment. This is because the air pressures used are not high enough to affect the lungs in most people.

You may feel breathless or have a cough. Tell your doctor or nurse at the treatment centre if this happens. It usually gets better when you finish your treatment.

Clinical trials for HBO treatment

Doctors think HBO treatment may be helpful when used with some cancer treatments. Research is trying to find out if HBO treatment can:

  • reduce the growth of some types of cancer when used in combination with radiotherapy
  • improve the effects of chemotherapy.

Cancer specialists use clinical trials to assess new treatments. Before a trial can start, an ethics committee must check it and agree that the trial is in the interest of patients.

You may be asked to take part in a clinical trial. Your doctor will discuss the treatment with you so that you understand what is involved. You may decide not to take part, or to withdraw from a trial at any stage. Your cancer doctor and specialist nurse will respect your decision. You do not have to give a reason for not taking part. Your decision will not change your care. Your cancer doctor will give you the standard treatment for the type and stage of cancer you have.

About our information

  • References

    Below is a sample of the sources used in our supportive treatment information. If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk

    M Heyboer III et al. Hyperbaric Oxygen Therapy: Side Effects Defined and Quantified. July 2017. Advances in Wound Care, Volume 6, Number 6 (accessed May 2019).

    D Mathieu et al. Tenth European Consensus Conference on Hyperbaric Medicine: recommendations for accepted and non-accepted clinical indications and practice of hyperbaric oxygen treatment. Diving Hyperb Med. 2017 Mar;47(1):24-32 (accessed May 2019).

    A Sultan et al. The Use of Hyperbaric Oxygen for the Prevention and Management of Osteoradionecrosis of the Jaw: A Dana-Farber/Brigham and Women’s Cancer Center Multidisciplinary Guideline. The Oncologist 2017;22:343-350 (accessed May 2019).


  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Chief Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.