Why am I short of breath? Shortness of breath causes

On this page, we explain the different causes that can make you feel breathless.

Breathlessness is a symptom. There are many possible underlying causes. But the main causes are:

There are other reasons too.

If you get breathless on a regular basis, you might have been diagnosed with one of these causes. Often there’s more than one. And others can develop over time. If you notice changes in your breathing, tell your doctor. Conditions that cause long-term breathlessness can often be treated to some extent, but some cannot be fully reversed. It’s important to learn how to manage long-term breathlessness, so that you can live as well as possible with it.

Lung conditions

Lung conditions cause breathlessness for many reasons. Some conditions cause the airways to become inflamed and narrowed, or fill the airways with phlegm, so it’s harder for air to move in and out of the lungs. Others make the lungs stiff and less elastic so it’s harder for them to expand and fill with air.

Lung conditions that cause long-term (chronic) breathlessness include:

Some lung conditions can also cause short-term (acute) breathlessness. These include:

  • a flare-up of asthma or COPD
  • a pulmonary embolism or blood clot on the lung
  • a lung infection such as pneumonia or tuberculosis
  • a pneumothorax or collapsed lung
  • a build-up of fluid in your lungs or the lining of your lungs – this might be because your heart is failing to pump efficiently or may be because of liver disease, cancer or an infection.

Heart conditions

Some people may experience long-term breathlessness due to heart failure. This can be due to problems with the rhythm, valves or cardiac muscles of the heart. Heart failure can cause breathlessness. This is because the heart can’t increase its pumping strength in response to exercise, or because the lungs become congested and filled with fluid. Often this is worse when lying flat so breathlessness due to heart failure can be worse at night or when asleep.

Heart conditions that cause acute breathlessness include:

  • a heart attack
  • an abnormal heart rhythm - you might feel your heart misses beats or you might experience palpitations.

Find out more on the British Heart Foundation website.


Some people feel short of breath when they’re anxious or afraid. This is a normal response by your body to what you think is a stressful situation – your body is preparing for action. As you get more anxious, you may start to breathe faster and tense your breathing muscles.

Your physical health can also impact on your mental health, especially if you are living with a lung condition. You might get anxious if you don’t feel in control of your condition. And if you have a lung condition, you may have symptoms that make you feel anxious. Sometimes the symptoms - like breathlessness, tightness in your chest or getting tired very easily - are similar to feelings of anxiety.

Panic attacks

When your body’s normal response is exaggerated, you get a rapid build-up of physical responses. This is a panic attack. Your breathing quickens and your body also releases hormones so your heart beats faster and your muscles tense.

During a panic attack, you might feel you can’t breathe and:

  • have a pounding heart
  • feel faint
  • sweat
  • feel sick
  • have shaky limbs

  • feel you’re not connected to your body

Panic attacks can be very frightening if you feel you can’t breathe.

If you start to breathe too quickly in response to a panic attack, you may breathe in more oxygen than your body needs. This is called hyperventilation or over-breathing. When you do this, the delicate balance of the gases in your lungs is upset. An amount of carbon dioxide normally stays in the blood. If you breathe in too much air too often, the carbon dioxide is pushed out through the lungs and this affects the messages the brain receives to tell you to breathe.

Being unfit or having an unhealthy weight

When we are unfit, our muscles get weaker. This includes the muscles we use to breathe. Weaker muscles need more oxygen to work, so the weaker our muscles, the more breathless we feel. It’s really important to keep active so you can manage your breathlessness better.

Being an unhealthy weight can also contribute to make us feel breathless.

  • If you’re underweight, your breathing muscles will be weaker.
  • If you’re overweight, it takes more effort to breathe and move around. Having more weight around the chest and stomach restricts how much your lungs can move. If you have a body mass index of 25 or more, you’re more likely to get breathless compared to people with a healthy weight.

People who are severely overweight can develop obesity hypoventilation syndrome. This is when poor breathing leads to lower oxygen levels and higher carbon dioxide levels in their blood.

Maintaining a healthy weight may help you to manage your breathlessness better and be more active. Read more about eating well for healthier lungs.

Other reasons

Other causes of long-term breathlessness include:

Next: Diagnosing the cause of breathlessness

Download our breathlessness information (PDF, 582KB)

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