Medically Reviewed by Paul Boyce, MD on November 04, 2023
4 min read

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

It happens when an infection causes the air sacs in your lungs (your doctor will call them alveoli) to fill 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 are at higher risk. 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. Causes include bacteria, viruses, and fungi.  If your pneumonia results from bacteria or a 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.

Your symptoms can vary depending on what’s causing your pneumonia, your age, and your overall health. They usually develop over several days.

Common pneumonia symptoms include:

  • Chest pain when you breathe or cough
  • Cough that produces phlegm or mucus
  • Fatigue and loss of appetite
  • Fever, sweating, and chills
  • Nausea, vomiting, and diarrhea
  • Shortness of breath

Along with these symptoms, older adults and people with weak immune systems might be confused or have changes in mental awareness, or they might have a lower-than-usual body temperature.

Newborns and infants may not show any signs of infection. Or they might vomit, have a fever and a cough, and seem restless or tired.

If you have a new cough, fever, or shortness of breath, call your doctor to ask about whether it could be COVID-19. Illness with the new coronavirus can also lead to pneumonia.

Bacteria, viruses, or fungi can cause pneumonia.

Common 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 who are in the hospital get “ventilator-associated pneumonia” if they got the infection while using a ventilator, a machine that helps you breathe.

If you get pneumonia while you’re in a hospital and aren’t 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.

Your doctor will start with questions about your symptoms and your medical history, like whether you smoke and whether you’ve been around sick people at home, school, or work. Then, they’ll listen to your lungs. If you have pneumonia, they might hear cracking, bubbling, or rumbling sounds when you breathe in.

If your doctor thinks you might have pneumonia, they’ll probably give you tests, including:

  • Blood tests to look for signs of a bacterial infection
  • A chest X-ray to find the infection in your lungs and how far it’s spread
  • Pulse oximetry to measure the level of oxygen in your blood
  • A sputum test to check the fluid in your lungs for the cause of an infection

If your symptoms started in the hospital or you have other health problems, your doctor might give you more tests, such as:

  • An arterial blood gas test to measure the oxygen in a small amount of blood taken from one of your arteries
  • Bronchoscopy to check your airways for blockages or other problems
  • A CT scan to get a more detailed image of your lungs
  • A pleural fluid culture, in which the doctor removes a small amount of fluid from the tissues around your lungs to look for bacteria that might cause pneumonia

Pneumonia can have complications, including:

  • Bacteremia, in which bacteria spread into your blood. This can cause septic shock and organ failure.
  • Trouble breathing, which might mean you need to use a breathing machine while your lungs heal.
  • Fluid buildup between the layers of tissue that line your lungs and chest cavity. This fluid can also become infected.
  • Lung abscess, when a pocket of pus forms inside or around your lung.

Your doctor can tell you which treatment is right for you.

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 before you’re through with it.

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

If your symptoms are severe or if you have other conditions that make you more likely to have complications, your doctor may send you to the hospital. While you’re there, your doctor will probably give you fluids or antibiotics through an IV tube. You may even need oxygen therapy or breathing treatments.

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