Learn About Pneumonia

Pneumonia is a common lung infection caused by bacteria, a virus or fungi. It often spreads via coughing, sneezing, touching or even breathing, and those who don't have symptoms can also spread it.

What Is Pneumonia?

Pneumonia is an infection of the lungs that may be caused by bacteria, viruses, or fungi. The infection causes the lungs' air sacs (alveoli) to become inflamed and fill up with fluid or pus. That can make it hard for the oxygen you breathe in to get into your bloodstream. The symptoms of pneumonia can range from mild to severe, and include cough, fever, chills, and trouble breathing.

Many factors affect how serious a case of pneumonia is, such as the type of germ causing the lung infection, the person’s age, and their overall health. The people most at risk are infants and young children, adults 65 or older, and people who have other health problems.

Pneumonia is a leading cause of hospitalization in both children and adults. Most cases can be treated successfully, although it can take weeks to fully recover. Tens of thousands of people in the U.S. die from pneumonia every year, most of them adults over the age of 65.

What Causes Pneumonia?

Pneumonia can be caused by a wide variety of bacteria, viruses and fungi in the air we breathe. Identifying the cause of your pneumonia can be an important step in getting the proper treatment.

Learn more about what causes pneumonia.

What Are the Risk Factors?

Anyone can get pneumonia, but many factors can increase your chances of getting sick and having a more severe illness. One of the most important factors is your age. People age 65 and over are at increased risk because their immune system is becoming less able to fight off infection as years go by. Infants and children two years of age or younger are also at increased risk because their immune systems are not yet fully developed.

Other risk factors can be grouped into three main categories: medical conditions, health behaviors, and environment.

Medical conditions

  • Chronic lung diseases such as COPD, bronchiectasis, or cystic fibrosis that make the lungs more vulnerable.
  • Other serious chronic illnesses, such as heart disease, diabetes and sickle cell disease.
  • A weakened immune system due to HIV/AIDs, an organ transplant, chemotherapy or long-term steroid use.
  • Difficulty swallowing, due to stroke, dementia, Parkinson's disease, or other neurological conditions, which can result in aspiration of food, vomit or saliva into the lungs that then becomes infected.
  • Recent viral respiratory infection—a cold, laryngitis, influenza, etc.
  • Hospitalization, especially when in intensive care and using a ventilator to breathe.

Health behaviors

  • Cigarette smoking, which damages the lungs.
  • Drug and alcohol abuse, which increase the risk of aspiration pneumonia.


  • Exposure to certain chemicals, pollutants or toxic fumes, including secondhand smoke.

Reviewed and approved by the American Lung Association Scientific and Medical Editorial Review Panel.

Page last updated: November 17, 2022

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