Sudden shortness of breath, or breathing difficulty (dyspnoea), 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's normal to get out of breath when you've overexerted yourself, but when breathlessness comes on suddenly and unexpectedly, it's usually a warning sign of a medical condition.

The information below outlines the most common reasons for:

sudden shortness of breath

long-term shortness of breath

This guide shouldn't be used to self-diagnose your condition, but should give you an idea of what's causing your breathlessness.


When to call a doctor

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 the result of anxiety, you may be asked to come to the surgery rather than a home visit.

If you've struggled with your breathing for a while, don't ignore it. See your GP as it's likely you have a long-term condition, such as obesity, asthma or chronic obstructive pulmonary disease (COPD), which needs to be managed properly.

Your doctor may ask you some questions, such as:

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've been active, or when you're 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?

Feeling like you can't get enough air can be terrifying, but doctors are well trained in managing this. You may be given extra oxygen to breathe if this is needed.


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'll produce more phlegm (sticky mucus), which causes you to wheeze and cough. You'll feel breathless because it's 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 delivers more medicine to your lungs, helping to relieve your breathlessness.

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

If you have COPD, it's likely your breathlessness is a sign this condition has suddenly got worse.


A heart problem 

It's 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're having a heart attack. If you or your GP think this is the case, they'll 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

A 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:

a severe allergic reaction (anaphylaxis)

pneumothorax – 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

pulmonary embolism – a blockage in one of the blood vessels in the lung

idiopathic pulmonary fibrosis – a rare and poorly understood lung condition that causes scarring of the lungs

pleural effusion – a collection of fluid next to the lung

diabetic ketoacidosis – a complication of diabetes where acids build up in your blood and urine

Causes of long-term breathlessness

Long-term breathlessness is usually caused by:

obesity or being unfit

poorly controlled asthma

chronic obstructive pulmonary disease (COPD) – permanent damage to the lungs usually caused by years of smoking

anaemia – a low level of oxygen in the blood caused by a lack of red blood cells or haemoglobin (the part of red blood cells that carries oxygen)

heart failure – when 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)

More unusual causes of long-term breathlessness are:

bronchiectasis – a lung condition where the airways are abnormally widened and you have a persistent phlegmy cough

pulmonary embolism – a recurrent blockage in a blood vessel in the lung

partial collapse of your lung caused by lung cancer

pleural effusion – a collection of fluid next to the lung

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)