Introduction 

Sudden shortness of breath, or breathing difficulty, is the most common reason for visiting a hospital accident and emergency department.

It's also one of the most common reasons people call 999 for an ambulance.

It is normal to get out of breath when you have over-exerted yourself, but when breathlessness comes on suddenly and unexpectedly, it is usually a warning sign of a medical condition. The medical name for it is dyspnoea.

What you should do

You should call your GP immediately if you have sudden shortness of breath, as there may be a problem with your airways or heart. Your GP will assess you over the phone and may either visit you at home or admit you to hospital. 

If your shortness of breath is due to anxiety, you may be asked to come to the surgery rather than a home visit.

Feeling that you cannot get enough air can be terrifying, but doctors are well trained in managing this. You will be given oxygen to breathe through a mask to help your symptoms while they investigate and treat the health condition causing your breathing problems.

If you have struggled with your breathing for a while, don't ignore it: see your GP as it is likely that you have a long-term condition, such as obesityasthma or chronic obstructive pulmonary disease, which will need managing properly.

The information below outlines the most common reasons for:

  • shortness of breath that has come on suddenly
  • shortness of breath that has lasted for a while

This guide should not be used to self-diagnose your condition, but should give you an idea of what is causing your breathlessness.

Causes of sudden shortness of breath

Sudden and unexpected breathlessness is most likely to be caused by one of the following health conditions. Click on the links below for more information about these conditions.

A problem with your lungs or airways

Sudden breathlessness could be an asthma attack. This means your airways have narrowed and you will produce more phlegm (sticky mucus), which will cause you to wheeze and cough. You will feel breathless because it will be difficult to move air in and out of your airways.

Your GP may advise you to use a spacer device with your asthma inhaler. This will deliver more medicine to your lungs, helping to relieve your breathlessness.

Pneumonia (lung inflammation) may also cause shortness of breath and a cough. It is usually caused by an infection, so you will need to take antibiotics.

If you have chronic obstructive pulmonary disease (COPD), it is likely your breathlessness is a sign this condition has suddenly got worse.

A heart problem 

It is possible to have a "silent" heart attack without experiencing all the obvious symptoms, such as chest pain and overwhelming anxiety. In this case, shortness of breath may be the only warning sign you are having a heart attack. If you or your GP think this is the case, they will give you aspirin and admit you to hospital straight away.

Heart failure can also cause breathing difficulties. This life-threatening condition means your heart is having trouble pumping enough blood around your body, usually because the heart muscle has become too weak or stiff to work properly. It leads to a build-up of water inside the lungs, which makes breathing more difficult.

A combination of lifestyle changes and medicines or surgery will help the heart pump better and relieve your breathlessness.

Breathlessness could also relate to a problem with your heart rate or rhythm, such as atrial fibrillation (an irregular and fast heart rate) or supraventricular tachycardia (regular and fast heart rate).

Panic attack or anxiety

panic attack or anxiety can cause you to take rapid or deep breaths, known as hyperventilating. Concentrating on slow breathing or breathing through a paper bag should bring your breathing back to normal.

More unusual causes

These include:

  • partial collapse of your lung caused by a small tear in the lung surface, which allows air to become trapped in the space around your lungs (this is known as pneumothorax)
  • a blockage in one of the blood vessels in the lung (known as a pulmonary embolism)
  • idiopathic pulmonary fibrosis, a rare and poorly understood lung condition that causes scarring of the lungs
  • a collection of fluid next to the lung (called pleural effusion)
  • a complication of diabetes known as diabetic ketoacidosis, where acids build up in your blood and urine

Causes of breathlessness that has lasted a while

Long-term breathlessness is usually caused by:

  • obesity or being unfit
  • asthma that is not controlled properly
  • chronic obstructive pulmonary disease (COPD), which is permanent damage to the lungs usually caused by years of smoking
  • anaemia, which is a low level of oxygen in the blood due to a lack of red blood cells or lack of haemoglobin (the part of red blood cells that carries oxygen)
  • heart failure, which means your heart is having trouble pumping enough blood around your body, usually because the heart muscle has become too weak or stiff to work properly
  • a problem with your heart rate or rhythm, such as atrial fibrillation (an irregular and fast heart rate) or supraventricular tachycardia (regular and fast heart rate).

Click on the links above for more information on these conditions.

More unusual causes of long-term breathlessness are:

  • a lung condition called bronchiectasis, where the airways are abnormally widened and you have a persistent phlegmy cough
  • a recurrent blockage in one of the blood vessels in the lung (known as a pulmonary embolism)
  • partial collapse of your lung caused by lung cancer
  • a collection of fluid next to the lung (pleural effusion)
  • narrowing of the main heart valve, restricting blood flow to the rest of the body
  • frequent panic attacks, which can cause you to hyperventilate (take rapid or deep breaths) 

Questions to think about while you are waiting for the doctor

  • Did the breathlessness come on suddenly or gradually?
  • Did anything trigger it, such as exercise?
  • How bad is it – does it only happen when you have been active, or when you are not doing anything?
  • Is there any pain when you breathe?
  • Do you have a cough?
  • Do certain positions make it worse – for example, are you unable to lie down?

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Page last reviewed: 19/02/2013

Next review due: 19/02/2015