What Is Pneumonia?

Pneumonia is a lung infection that can be mild or so severe that you have to go to the hospital.

It happens if an infection 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.

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.

You can get pneumonia in 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. 

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


Bacteria, viruses, or fungi can cause pneumonia.

Top causes include:

  • Flu viruses
  • Cold viruses
  • RSV virus (the top cause of pneumonia in babies age 1 or younger
  • Bacteria called Streptococcus pneumoniae and Mycoplasma pneumoniae

Some people get “ventilator-associated pneumonia” if they got the infection while on a ventilator, which is a machine at a hospital that helps you breathe.

If you got your pneumonia while you were in a hospital and not on a ventilator, that’s called “hospital-acquired” pneumonia. But most people get “community-acquired pneumonia,” which means they didn’t get it in a hospital.


If you have bacterial pneumonia, you’ll get antibiotics. Make sure you take all of the medicine your doctor gives you, even if you start to feel better.

If you have viral pneumonia, antibiotics won’t help. You’ll need to rest, drink a lot of fluids, and take medicines for your fever.

You may need to go to a hospital if your symptoms are severe or if you have other conditions that make you more likely to have complications. 

With any kind of pneumonia, you’re going to need lots of rest. You might need a week off your usual routines, but you might still feel tired for a month.

WebMD Medical Reference Reviewed by Carol DerSarkissian on September 13, 2017



National Heart, Lung, and Blood Institute: “Pneumonia,” “Explore Pneumonia: Treatment,” and “Explore Pneumonia: Living With.”

Kids Health: “Pneumonia.”

CDC: “Pneumonia: An Infection of the Lungs.”


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