What is pneumonia?

Pneumonia is an infection in one or both of your lungs that can be caused by several kinds of germs, such as:

  • Bacteria
  • Viruses
  • Fungi (molds) (uncommon)

Pneumonia causes swelling (inflammation) of the airways and causes air sacs in the lungs to fill with mucus and other fluids, making it difficult for oxygen to reach the blood.


What are the types of pneumonia?

  • Bacterial Pneumonia: Bacterial pneumonia is caused by bacteria germs. The streptococcus pneumoniae germ is the most common cause of bacterial pneumonia.
  • Viral Pneumonia: Viral pneumonia is caused by virus germs. About half of all people with pneumonia have viral pneumonia. Viral pneumonia is usually less serious than bacterial pneumonia.

How Your Lungs Work

Your lungs' main job is to get oxygen into your blood and remove carbon dioxide. This happens during breathing. We breathe 12 to 20 times per minute when we are not sick. When you breathe in, air travels down the back of your throat and passes through your voice box and into your windpipe (trachea). Your trachea splits into two air passages (bronchial tubes). One bronchial tube leads to the left lung, the other to the right lung. For the lungs to perform their best, the airways need to be open as you breathe in and out. Swelling (inflammation) and mucus can make it harder to move air through the airways, making it harder to breathe. This leads to shortness of breath, difficulty breathing, and feeling more tired than normal.

air passages

What are the signs and symptoms of both bacterial and viral pneumonia?

  • Bacterial Pneumonia: Symptoms of bacterial pneumonia can develop gradually or suddenly. Symptoms include:
    • High fever (up to 105 degrees)
    • Tiredness (less energy)
    • Rapid breathing
    • Chills
    • Cough with mucus (might be greenish or have blood)
    • Chest pain, especially with coughing or deep breathing
    • Shortness of breath
    • Loss of appetite
  • Viral Pneumonia: Symptoms usually develop over a period of several days. Early symptoms are similar to flu symptoms, which include:
    • Fever
    • Dry cough
    • Headache
    • Sore throat
    • Loss of appetite
    • Muscle pain
    • Additional symptoms about a day later:
      • High fever
      • Cough with mucus
      • Shortness of breath

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy