Pneumonia is swelling (inflammation) of the tissue in one or both lungs. It's usually caused by a bacterial infection.

At the end of the breathing tubes in your lungs are clusters of tiny air sacs.

If you have pneumonia, these tiny sacs become inflamed and fill up with fluid.

Symptoms of pneumonia

The symptoms of pneumonia can develop suddenly over 24 to 48 hours, or they may come on more slowly over several days.

Common symptoms of pneumonia include:

• a cough – which may be dry, or produce thick yellow, green, brown or blood-stained mucus (phlegm)
• difficulty breathing – your breathing may be rapid and shallow, and you may feel breathless, even when resting
• rapid heartbeat
• high temperature
• feeling generally unwell
• sweating and shivering
• loss of appetite
• chest pain – which gets worse when breathing or coughing

Less common symptoms include:

• coughing up blood (haemoptysis)
• headaches
• fatigue
• feeling sick or being sick
• wheezing
• joint and muscle pain
• feeling confused and disorientated, particularly in elderly people

When to see a GP

See a GP if you feel unwell and you have typical symptoms of pneumonia.

Seek urgent medical attention if you're experiencing severe symptoms, such as rapid breathing, chest pain or confusion.

Who's affected

In the UK, pneumonia affects around 0.5 to 1% of adults each year. It's more widespread in autumn and winter.

Pneumonia can affect people of any age, but it's more common, and can be more serious, in certain groups of people, such as the very young or the elderly.

People in these groups are more likely to need hospital treatment if they develop pneumonia.

What causes pneumonia

Pneumonia is usually the result of a pneumococcal infection, caused by bacteria called Streptococcus pneumoniae.

Many different types of bacteria, including Haemophilus influenzae and Staphylococcus aureus, can also cause pneumonia, as well as viruses and, more rarely, fungi.

As well as bacterial pneumonia, other types include:

• viral pneumonia – most commonly caused by the respiratory syncytial virus (RSV) and sometimes influenza type A or B; viruses are a common cause of pneumonia in young children
• aspiration pneumonia – caused by breathing in vomit, a foreign object, such as a peanut, or a harmful substance, such as smoke or a chemical
• fungal pneumonia – rare in the UK and more likely to affect people with a weakened immune system
• hospital-acquired pneumonia – pneumonia that develops in hospital while being treated for another condition or having an operation; people in intensive care on breathing machines are particularly at risk of developing ventilator-associated pneumonia

Risk groups

The following groups have an increased risk of developing pneumonia:

• babies and very young children
• elderly people
• people who smoke
• people with other health conditions, such as asthma, cystic fibrosis, or a heart, kidney or liver condition
• people with a weakened immune system – for example, as a result of a recent illness, such as flu, having HIV or AIDS, having chemotherapy, or taking medicine after an organ transplant

Diagnosing pneumonia

A GP may be able to diagnose pneumonia by asking about your symptoms and examining your chest.

Further tests may be needed in some cases.

Pneumonia can be difficult to diagnose because it shares many symptoms with other conditions, such as the common cold, bronchitis and asthma.

To help make a diagnosis, a GP may ask you:

• whether you feel breathless or you're breathing faster than usual
• how long you have had your cough, and whether you're coughing up mucus and what colour it is
• if the pain in your chest is worse when you breathe in or out

A GP may also take your temperature and listen to your chest and back with a stethoscope to check for any crackling or rattling sounds.

They may also listen to your chest by tapping it. Lungs filled with fluid produce a different sound from normal healthy lungs.

If you have mild pneumonia, you probably will not need to have a chest X-ray or any other tests.

You may need a chest X-ray or other tests, such as a sputum (mucus) test or blood tests, if your symptoms have not improved within 48 hours of starting treatment.

Treating pneumonia

Mild pneumonia can usually be treated at home by:

• getting plenty of rest
• taking antibiotics
• drinking plenty of fluids

If you do not have any other health problems, you should respond well to treatment and soon recover, although your cough may last for some time.

It's usually safe for someone with pneumonia to be around others, including family members.

But people with a weakened immune system are less able to fight off infections, so it's best they avoid close contact with a person with pneumonia.

For at-risk groups, pneumonia can be severe and may need to be treated in hospital.

This is because it can lead to serious complications, which in some cases can be fatal, depending on a person's health and age.

Complications of pneumonia

Complications of pneumonia are more common in young children, the elderly and those with pre-existing health conditions, such as diabetes.

Possible complications of pneumonia include:

• pleurisy – where the thin linings between your lungs and ribcage (pleura) become inflamed, which can lead to respiratory failure
• a lung abscess – a rare complication that's mostly seen in people with a serious pre-existing illness or a history of severe alcohol misuse
• blood poisoning (sepsis) – also a rare but serious complication

You'll be admitted to hospital for treatment if you develop one of these complications.

Preventing pneumonia

Although most cases of pneumonia are bacterial and are not passed on from one person to another, ensuring good standards of hygiene will help prevent germs spreading.

For example, you should:

• cover your mouth and nose with a handkerchief or tissue when you cough or sneeze
• throw away used tissues immediately – germs can live for several hours after they leave your nose or mouth
• wash your hands regularly to avoid transferring germs to other people or objects

A healthy lifestyle can also help prevent pneumonia. For example, you should avoid smoking as it damages your lungs and increases the chance of infection.

Find out how to stop smoking

Excessive and prolonged alcohol misuse also weakens your lungs' natural defences against infections, making you more vulnerable to pneumonia.

People at high risk of pneumonia should be offered the pneumococcal vaccine and flu vaccine.