Breathlessness and what can cause it

If you are breathless, you may experience uncomfortable or fast breathing. You may feel short of breath or your chest may feel tight. Different causes of breathlessness include:

  • cancer affecting the lungs
  • a build-up of fluid in the lungs or stomach
  • low levels of red blood cells
  • chest infections
  • weak muscles
  • pain
  • blood clots
  • smoking
  • anxiety
  • cancer treatments.

Your doctor can explain the cause of your breathlessness and help you find the best treatment. Your doctor may suggest using a Borg scale to show how breathless you feel at different times. A Borg scale uses numbers 0 to 10, with 10 being severe breathlessness. You can use this to keep a diary of your breathlessness. This may help you know what makes it worse so you can manage your activities.

If you feel depressed or isolated because of your breathlessness, speak to your GP about medicines or counseling that may help you.

The lungs

We have two lungs – one on each side of the chest. When we breathe in, air passes from our nose or mouth down through a tube called the windpipe (trachea). The windpipe divides into two tubes (airways), one going to each lung. These tubes are known as the right and left bronchus. They divide to form smaller tubes called bronchioles, which carry air through the lungs.

At the end of the bronchioles are millions of tiny air sacs called alveoli. In the alveoli, oxygen is absorbed from the air we breathe in. This oxygen passes into the bloodstream to be circulated around the body.

Carbon dioxide is a waste gas that needs to be removed from the body. It passes from the bloodstream into the alveoli and is then breathed out by the lungs.

Just below the lungs is a sheet of muscle called the diaphragm. The diaphragm and the muscles between the ribs contract and relax in order to suck air into and push air out of the lungs. They are the main muscles used for breathing when you’re relaxed.

During heavy exercise, the muscles in your shoulders and upper chest can also help with breathing. These muscles are not designed to work for long periods of time and get tired easily.

The lungs are covered by a lining (membrane) called the pleura, which has an inner and outer layer. The inner layer covers the lungs. The outer layer lines the ribcage and the diaphragm. The pleura produces a fluid that acts as a lubricant, which allows the lungs to move in and out smoothly.

Upper airways and the lungs
Upper airways and the lungs

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Causes of breathlessness

There are different causes of breathlessness. Your doctor should be able to tell you the cause of your breathlessness so that you can get the most helpful treatment. If your breathlessness gets worse quickly or you have pain when you breathe, contact your doctor immediately as you may need urgent treatment.

Cancer affecting the lungs

This can be:

  • primary lung cancer (cancer that started in the lungs)
  • a secondary cancer that has spread to the lungs from another part of the body. 

Treatments such as radiotherapy or chemotherapy may help shrink the tumour and relieve breathlessness caused by the cancer. We have information about the type of cancer you have and its treatments.

A build-up of fluid in the lining of the lungs (pleural effusion) or abdomen (ascites)

If cancer cells irritate the lining of the lungs or stomach, this can cause a build-up of fluid. This means there is less room for the lungs to expand. Pleural effusion and ascites can be treated by draining the fluid. We have more information about these conditions.

Low levels of red blood cells in the blood (anaemia)

This can be due to the cancer or its treatment, such as chemotherapy or radiotherapy. Red blood cells carry oxygen around the body. If the level of red blood cells in your blood is low, you may become very tired and breathless.

Your doctors may recommend that you have a blood transfusion

Chest infections

These cause phlegm in the airways and can make you feel breathless. Drinking a good amount of fluid will make the phlegm easier to move so you can cough it up more easily. If you develop a high temperature (above 37.5°C or 99.5F), a chesty cough or pain when you breathe, contact your doctor immediately as you may need antibiotics.

Weakened muscles

In advanced cancer, the muscles that help breathing can become weak because of fatigue, lack of nutrition, weight loss and reduced physical activity. This can make breathing more difficult.


Pain can make it difficult to breathe and move comfortably. Tell your doctor about any pain you’re experiencing so they can make sure it’s being managed effectively.

A blood clot in the lung (pulmonary embolism) 

This can cause sudden breathlessness and pain when you breathe. If you have these symptoms, contact your doctor immediately.

Other conditions

Some other conditions can cause breathlessness, such as congestive heart failure, asthma, chronic obstructive pulmonary disease (COPD) and pulmonary oedema, which is a build-up of fluid in the air sacs (alveoli) in the lungs. Your doctor can advise you about the treatment you need.

Smoking tobacco

Smoking makes breathlessness worse. The smoke causes irritation and inflammation of the airways. This means less oxygen is absorbed into the bloodstream. If you want to stop smoking, ask your nurse or doctor about help that’s available locally, such as free local NHS Stop Smoking Services. We have more information about giving up smoking.

Cancer treatments

Surgery for lung cancer may involve removing part, or all, of a lung. Many people are able to breathe well once they recover from surgery, but some people do have breathing problems.

Radiotherapy to the chest can cause inflammation of the lung (pneumonitis), which can lead to breathlessness. This is usually a short-term problem, but for some people it can be a long-term problem. People who have intensive radiotherapy to the chest can sometimes develop hardening and thickening (scarring) of the lung, which can cause long-term breathlessness.

Some chemotherapy drugs, such as bleomycin, cyclophosphamide or methotrexate, can sometimes cause breathing problems.

Your cancer specialist can tell you about any effects your treatment may have on your breathing, and answer any questions you have. 

If you experience breathlessness, always let your doctor know.

Anxiety and panic

Feelings of anxiety and panic are common. They are natural reactions after a cancer diagnosis and during treatment. They can cause some people to have rapid and shallow breathing. Becoming breathless can itself cause more anxiety and panic. We have more information on this below.  

Feeling anxious

Being breathless may sometimes cause you to feel anxious. Some people feel as though they are having a panic attack.

Common symptoms of anxiety and panic are:

  • heart palpitations
  • feeling sick
  • sweating
  • a dry mouth
  • dizziness.

Anxiety may cause you to breathe too fast and to take shallow breaths from the top of your lungs rather than your lower chest. This can make you feel more breathless, which in turn can increase the anxiety.

A way to break this cycle of anxiety is to gradually slow your breathing rate, and use controlled breathing exercises or relaxation techniques. Our CD Relax and Breathe might also help. Using a handheld fan to blow air onto your face, and breathing out against the fan, may also help calm your breathing.

Some people may need to take medication to help them manage their anxiety.

If you notice there are times when you hyperventilate (overbreathe), try to identify what triggered it. Talking about the cause with family or friends may help, because then they will be aware of it next time.

Indicating how breathless you are

Using a Borg scale

When you become breathless, it may help to give your family, friends and healthcare professionals a clear idea of how bad the breathlessness is. You can use the score when phoning your health professional — this can help them to understand how much support you need at the time. We’ve added a Borg scale below to help you do this. A Borg scale can be used to give your breathlessness a number:

  • 0 being no breathlessness at all
  • 10 being the most severe breathlessness.

A Borg scale can also help you to be aware of your breathing and how it changes, especially when carrying out activities.

You might want to point to the scale during episodes of breathlessness, to communicate to others how you’re feeling when you don’t want to use your breath to talk.

0Nothing at all
0.5Very, very slight (just noticeable)
1Very slight
2Slight (light)
4Somewhat severe
5Severe (heavy)
7Very severe
10Very, very severe

Your feelings about breathlessness

Your feelings may change at different times during your illness.

Some days you may feel well and relaxed, while on others you may feel frightened, stressed, angry, sad and even guilty. These are normal responses to breathlessness, the cancer, the treatment and any fears you have about the future. There’s no right or wrong way to deal with these feelings, but accepting they are normal will help.

Sometimes you may feel that you need to be alone, while at other times you may want to be with people. Do what feels right for you at the time where possible. You may have family and friends who find your changing emotions difficult to understand.

Try talking together about how you each feel. This can help you understand each other better and be able to cope with the problems more easily.

You may find it helpful to talk to other people who are going through similar experiences. You can find out about support groups in your area by calling us on 0808 808 00 00. You can also share your experiences of breathlessness with others on our Online Community.

Feeling depressed

Many people feel sad as a result of their cancer and difficult symptoms such as breathlessness. This is a natural response. Sometimes, these feelings of sadness don’t seem to pass but get worse and you may become depressed.

Depression can come on gradually and may be difficult to recognise. If you’re depressed, it may be harder for you to follow your treatment plan or your health professionals’ advice.

Depression can usually be successfully treated in most people. The first step to feeling better is getting appropriate help. If you or your family think you may be depressed, discuss it with your GP. They can prescribe an antidepressant drug for you, or refer you to a doctor or counsellor who specialises in the emotional problems that people with cancer might experience. By getting depression treated, you’ll make life easier for yourself, your family and your friends.

Feeling isolated

People with breathlessness can sometimes become isolated if they’re less able to go out and meet family or friends.

Talking in a large group of people can also be very tiring. You may feel that you’d rather avoid these types of social situations. If you do feel isolated, it may help to talk to your family and friends. Tell them how you feel and how much you’re able to do. Together, you may be able to find a way to continue seeing each other that is less tiring for you.

We have more information about the emotional effects of cancer.

'Give us a call, we're here to listen.'

Zahida from our support line talks about how giving us a call can help.

More about our support line

'Give us a call, we're here to listen.'

Zahida from our support line talks about how giving us a call can help.

More about our support line

Back to Cancer and breathlessness

Relaxation techniques

You may want to try using relaxation techniques to help you manage your anxiety and reduce breathlessness.