Pneumonia | Overview


What is pneumonia?

Pneumonia is an infection of the lungs. Your lungs have 2 main parts: airways (also called bronchial tubes) and alveoli (also called air sacs). When you breathe, the air moves down through your airways and into your alveoli (say: "al-vee-oh-lie"). From the alveoli, oxygen goes into your blood while carbon dioxide moves out of your blood. When you have pneumonia, your alveoli get inflamed (irritated and swollen) and fill with fluid. This makes it difficult for you to breathe.

Pneumonia is usually caused by bacteria or a virus. It can also be caused by fungi or irritants that you breathe into your lungs.

What are the different types of pneumonia?

There are 4 types of pneumonia: 

  • Community-acquired pneumonia is the most common type of pneumonia. You can catch it in public areas (such as work, school, the grocery store or the gym). Bacteria, a virus, fungi or irritants in the air can cause community-acquired pneumonia. The bacteria Streptococcus pneumoniae is the most common cause of this type of pneumonia. This type of pneumonia can also develop after you have a cold or the flu.
  • Hospital-acquired pneumonia (also called institution-acquired pneumonia) is a type of pneumonia that you can catch while you are staying in the hospital, especially if you are staying in an intensive care unit (ICU) or are using a ventilator to help you breathe. This type of pneumonia also includes pneumonia that develops after you have major surgery (such as chest surgery) and pneumonia that develops while staying in or receiving treatment in kidney dialysis centers and chronic care centers. It can be very dangerous, especially for young children, older adults and people who have weakened immune systems.
  • Aspiration pneumonia is type of pneumonia that develops after you inhale particles into your lungs. This occurs most often when small particles enter your lungs after vomiting and you are not strong enough to cough the particles out of your lungs.
  • Opportunistic pneumonia is a type of pneumonia that affects people who have weakened immune systems. It is caused by certain organisms that do not typically make healthy people sick, but they can be dangerous for people who have conditions such as the human immunodeficiency virus (HIV), acquired immunodeficiency syndrome (AIDS), chronic obstructive pulmonary disease (COPD) or people who have recently had an organ transplant.


This information was developed as part of an educational program made possible through support from Wyeth Vaccines.

Written by editorial staff

Reviewed/Updated: 04/14
Created: 03/09