What Is Pneumonia?

Pneumonia is an infection that causes the air sacs of the lungs (doctors call these “alveoli”) to fill up with fluid or pus. That can make it hard for you to breathe in enough oxygen to reach your bloodstream.

Pneumonia can be caused by bacteria, viruses, or fungi. It can affect one or both lungs. You can also have it and not know it. Doctors call this “walking pneumonia.”

If your pneumonia is caused by a bacteria or virus, you can spread it to someone else. 

Anyone can get this lung infection. But infants younger than age 2 and people over age 65 have the highest odds. That’s because their immune systems might not be strong enough to fight it.

Lifestyle factors, like smoking cigarettes and drinking too much alcohol, can also increase your chances of getting pneumonia.

WebMD Medical Reference Reviewed by Minesh Khatri, MD on March 27, 2017



National Heart, Lung, and Blood Institute: “Pneumonia.”

Kids Health: “Pneumonia.”


© 2017 WebMD, LLC. All rights reserved.