Pneumonia: What to Know

What Is Pneumonia?

Pneumonia is a lung infection that can range from mild to so serious that you have to go to the hospital. It happens when an infection causes air sacs in your lungs (the alveoli) and tubes in your airways that connect to them (bronchioles) to fill with fluid or pus. That can make it hard for you to breathe in enough oxygen.

Anyone can get this lung infection. But children younger than 2 and adults 50 years old and up are at higher risk. That’s because their immune systems might not be strong enough to fight it. Lifestyle habits, like smoking cigarettes and drinking too much alcohol, can also raise your chances of getting pneumonia.

You can get pneumonia in one or both lungs. Pneumonia in both lungs is sometimes called bilateral pneumonia or double pneumonia. You can also have pneumonia and not know it. This is sometimes called walking pneumonia.

Causes include bacteria, viruses, and fungi. If your pneumonia results from bacteria or a virus, you can spread it to someone else.

Types of Pneumonia

Pneumonia can be grouped into types based on what caused it. Many things can lead to pneumonia, but some of the most common are:

Bacterial pneumonia

More people get this type of pneumonia than any other. While several types of bacteria can cause it, the most common in the U.S. is streptococcus. People sometimes get bacterial pneumonia after a viral infection like a cold or the flu.

Viral pneumonia

Viruses, such as cold and flu viruses, cause about a third of all cases of pneumonia. They're the most common cause of the condition in children under 5. This type of infection isn't usually as serious as bacterial pneumonia, but it can be. Viral pneumonia raises your risk of also getting bacterial pneumonia.

Fungal pneumonia

Fungi found in dirt or bird poop can also cause a pneumonia infection. This type is more likely to affect people with weaker immune systems, such as those who have long-lasting health problems.

Walking pneumonia

This is a nickname for a less serious type that's officially called mycoplasma pneumonia. It's named for the bacteria that causes it. Young adults and older children most often get this type, which often doesn't require bed rest.