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Diseases A–Z


Causes | Signs & Symptoms | Diagnosis | Prevention

What is pneumonia?

Pneumonia is an infection of the lungs. Many different germs can cause pneumonia, including bacteria, viruses, and fungi. When you breathe in these germs, they can settle in the air sacs (alveoli) of your lungs. Deep in your lungs, the germs may grow and overcome your body's normal defenses.

After they become infected, the air sacs then fill with pus and mucus. This swelling (inflammation) of the air sacs makes them less stretchy and keeps oxygen from properly reaching your blood stream.

As you work harder to breathe and give your body oxygen, you can feel short of breath. The swelling also causes many of the other symptoms of pneumonia like cough, fever, and chest pain.

There are many different kinds of pneumonia — some are milder and some are very serious. Pneumonia can even be life-threatening. It's a leading cause of death and hospitalization in seniors and in people with long-term (chronic) diseases. The good news is that there are many things you can do to lower your risk of getting pneumonia.

Learn more about these types of pneumonia:

  • Bacterial pneumonia
  • Viral pneumonia
  • Mycoplasma pneumonia
  • Other types of pneumonia

  • Illustration of lobar pneumonia
    Lobar pneumonia
    What causes pneumonia?

    Pneumonia is not a single disease. It can have over thirty different causes. You can get it from different types of germs. You can also get it from breathing in (aspirating) food, liquid, chemicals and dust.

    Pneumonia can also affect different parts of the lungs:

    • Lobar pneumonia affects a section (lobe) of the lung.
    • Bronchial pneumonia affects the lungs in patches around the tubes which bring the air into the lungs (these are called bronchi or bronchioles).
    • Illustration of bronchial pneumonia
      Bronchial pneumonia

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      Signs and symptoms of penumonia

      The signs and symptoms of pneumonia can range from mild to serious. It depends on your age and what type of pneumonia you have. Some of the most common symptoms include:

      • cough
      • yellow-green phlegm (mucus)
      • shortness of breath
      • feeling very tired and unwell
      • chest pain
      • fever
      Diagnosis of pneumonia

      Your doctor will do tests to confirm that you have pneumonia. Some of these tests may include:

      • sputum tests (lab tests done on the mucus or phlegm that you cough up from your lungs)
      • blood tests
      • chest X-rays
      Preventing pneumonia

      Some of the germs that can cause pneumonia are easily spread from person to person. They are carried in the nose and throat of an infected person. When an infected person coughs, they spray drops of infected saliva (spit) into the air around them. A person who breathes in that air can get pneumonia.

      There are things you can do to reduce your risk of getting pneumonia:

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