Pneumonia, caused by bacteria. Figure A shows pneumonia affecting part of the left lung. Figure B shows healthy alveoli (air sacs). Figure C shows alveoli filled with mucus.
Pneumonia, caused by bacteria. Figure A shows pneumonia affecting part of the left lung. Figure B shows healthy alveoli (air sacs). Figure C shows alveoli filled with mucus.

Pneumonia is an infection that affects one or both lungs. It causes the air sacs, or alveoli, of the lungs to fill up with fluid or pus. Bacteria, viruses, or fungi may cause pneumonia. Symptoms can range from mild to serious and may include a cough with or without mucus (a slimy substance), fever, chills, and trouble breathing. How serious your pneumonia is depends on your age, your overall health, and what is causing your infection.

To diagnose pneumonia, your doctor will review your medical history, perform a physical exam, and order diagnostic tests such as a chest X-ray. This information can help your doctor determine what type of pneumonia you have.

Treatment for pneumonia may include antibiotics or viral or fungal medicines. It may take several weeks to recover from pneumonia. If your symptoms get worse, you should see a doctor right away. If you have severe pneumonia, you may need to go to the hospital for antibiotics given through an intravenous (IV) line and oxygen therapy.

Explore this Health Topic to learn more about pneumonia, our role in clinical trials, and where to find more information.

Causes - Pneumonia

Most of the time your body filters germs out of the air that you breathe. Sometimes germs, such as bacteria, viruses, or fungi, get into your lungs and cause infections.

When these germs get into your lungs, your immune system, which is your body's natural defense against germs, goes into action. Immune cells attack the germs and may cause inflammation of your air sacs, or alveoli. Inflammation can cause your air sacs to fill up with fluid and pus and cause the symptoms of pneumonia. Watch the video below to learn more. You can also learn more about How the Lungs Work in our Health Topic.

This video shows how your immune system tries to get rid of germs in your respiratory system and how you develop pneumonia. Medical Animation Copyright © 2020 Nucleus Medical Media Inc. All rights reserved.


Bacteria are a common cause of pneumonia in adults. Many types of bacteria can cause pneumonia, but Streptococcus pneumoniae (also called pneumococcus bacteria) is the most common cause in the United States. 

Some bacteria cause pneumonia with different symptoms or other characteristics than “typical” pneumonia. This infection is called atypical pneumonia. For example, Mycoplasma pneumoniae causes a mild form of pneumonia often called “walking pneumonia.” Legionella pneumophila causes a severe type of pneumonia called Legionnaires’ disease. Bacterial pneumonia can happen on its own or develop after you have had a cold or the flu.


Viruses that infect your lungs and airways can cause pneumonia. The flu (influenza virus) and the common cold (rhinovirus) are usually the most common causes of viral pneumonia in adults. Respiratory syncytial virus (RSV) is the most common cause of viral pneumonia in young children.

Many other viruses can cause pneumonia, including SARS-CoV-2, the virus responsible for COVID-19. Watch our video on how SARS-CoV-2 affects the lungs to learn more. Additionally, we offer information and resources on how we are working hard to support necessary COVID-19 research. 


Fungi such as Pneumocystis jirovecii may cause pneumonia, particularly in people who have weakened immune systems. Some fungi found in the soil in the southwestern United States and in the Ohio and Mississippi River valleys can cause pneumonia.

Risk Factors - Pneumonia

Your risk of pneumonia may be higher because of your age, environment, lifestyle habits, and other medical conditions.


Pneumonia can affect people of all ages. However, two age groups are at higher risk of developing pneumonia and having more serious pneumonia.

  • Babies and children, 2 years old or younger, because their immune systems are still developing. The risk is higher for premature babies.
  • Older adults, age 65 or older, because their immune systems generally weaken as they age. Older adults are also more likely to have other chronic (long-term) health conditions that raise the risk of pneumonia. 

Babies, children, and older adults who do not get the recommended vaccines to prevent pneumonia have an even higher risk.

Environment or occupation

Most people get pneumonia when they catch an infection from someone else in their community. Your chance of getting pneumonia is higher if you live or spend a lot of time in a crowded place such as a military barrack, prison, homeless shelter, or nursing home. 

Your risk is also higher if you regularly breathe in air pollution or toxic fumes. 

Some germs that cause pneumonia can infect birds and other animals. You are most likely to encounter these germs if you work in a chicken or turkey processing center, pet shop, or veterinary clinic.

Lifestyle habits

  • Smoking cigarettes can make you less able to clear mucus from your airways.
  • Using drugs or alcohol can weaken your immune system. You are also more likely to accidentally inhale saliva or vomit into your windpipe if you are sedatedor unconscious from an overdose.

Other medical conditions

You may have an increased risk of pneumonia if you have any of the following medical conditions.

  • Brain disorders, such as a stroke, a head injury, dementia, or Parkinson’s disease. These conditions can affect your ability to cough or swallow. This can lead to food, drink, vomit, or saliva going down your windpipe instead of your esophagus and getting into your lungs.
  • Conditions that weaken your immune system, such as pregnancy, HIV/AIDS, or an organ or bone marrow transplant. Chemotherapy, which is used to treat cancer, and long-term use of steroid medicines can also weaken your immune system.
  • Critical diseases that require hospitalization. Receiving treatment in a hospital intensive care unit raises your risk of hospital-acquired pneumonia. Your risk is higher if you cannot move around much or are sedated or unconscious. Using a ventilator raises the risk of a type called ventilator-associated pneumonia.
  • Lung diseases, such as asthma, bronchiectasis, cystic fibrosis, or COPD.
  • Other serious conditions, such as malnutrition, diabetes, heart failure, sickle cell disease, or liver or kidney disease.

Screening and Prevention - Pneumonia

Pneumonia can be very serious and even life-threatening. Vaccines can help prevent some types of pneumonia. Good hygiene (washing your hands often), quitting smoking, and keeping your immune system strong by getting regular physical activity and eating healthy are other ways to lower your risk of getting pneumonia.


Vaccines can help prevent pneumonia caused by pneumococcus bacteria or the flu virus. Vaccines cannot prevent all cases of pneumonia. However, compared to people who don't get vaccinated, those who are vaccinated and still get pneumonia tend to have:

  • Fewer serious complications
  • Milder infections
  • Pneumonia that doesn’t last as long

Pneumococcus vaccines

Two vaccines are available to prevent infections from the pneumococcus bacteria, the most common type of bacteria that causes pneumonia. Pneumococcus vaccines are especially important for people at high risk of pneumonia, including:

  • Adults age 65 or older
  • Children age 2 or younger
  • People who have chronic (ongoing) diseases, serious long-term health problems, or weak immune systems. This may include people who have cancer, HIV, asthma, sickle cell disease, or damaged or removed spleens.
  • People who smoke

For more information, visit the CDC’s Pneumococcal Vaccination and Pneumococcal Vaccination: Summary of Who and When to Vaccinate pages.

Flu (influenza) vaccine

Your yearly flu vaccine can help prevent pneumonia caused by the flu. The flu vaccine is usually given in September through October, before flu season starts.

For more information about the flu vaccine, visit the CDC's Seasonal Influenza (Flu) Vaccination and Who Needs a Flu Vaccine and When webpages.

Hib vaccine

Haemophilus influenzae type b (Hib) is a type of bacteria that can cause pneumonia and meningitis. The Hib vaccine is recommended for all children under 5 years old in the United States. The vaccine often is given to infants starting when they are 2 months old.

For more information about the Hib vaccine, go to the CDC's Hib Vaccination webpage.

Other ways to prevent pneumonia

You can take the following steps to help prevent pneumonia:

  • Wash your hands with soap and water or alcohol-based hand sanitizers to kill germs.
  • Don’t smoke. Smoking prevents your lungs from properly filtering out and defending your body against germs. For information about how to quit smoking, visit Smoking and Your Heart and Your Guide to a Healthy Heart. These resources include basic information about how to quit smoking. For free help and support, you may call the National Cancer Institute’s Smoking Quitline at 1-877-44U-QUIT (1-877-448-7848).
  • Keep your immune system strong. Get plenty of physical activity and follow a healthy eating plan. Read more about heart-healthy living.
  • If you have problems swallowing, eat smaller meals of thickened food and sleep with the head of your bed raised up. These steps can help you avoid getting food, drink, or saliva into your lungs.
  • If you have a planned surgery, your doctor may recommend that you don’t eat for 8 hours or drink liquids for 2 hours before your surgery. This can help prevent food or drink from getting into your airway while you are sedated.
  • If your immune system is impaired or weakened, your doctor may recommend you take antibiotics to prevent bacteria from growing in your lungs.

Signs, Symptoms, and Complications - Pneumonia

The signs and symptoms of pneumonia can be mild or serious. Young children, older adults, and people who have serious health conditions are at risk for developing more serious pneumonia or life-threatening complications.

Signs and symptoms

The signs and symptoms of pneumonia may include:

  • Chest pain when you breathe or cough
  • Chills
  • Cough with or without mucus
  • Fever
  • Low oxygen levels in your blood, measured with a pulse oximeter
  • Shortness of breath

You may also have other symptoms, including a headache, muscle pain, fatigue (extreme tiredness), nausea (feeling sick to your stomach), vomiting, and diarrhea.

Older adults and people who have serious illnesses or weakened immune systems may not have typical symptoms. They may have a lower than normal temperature instead of a fever. Older adults who have pneumonia may feel weak or suddenly confused.

Sometimes babies don’t have typical symptoms either. They may vomit, have a fever, cough, or appear restless or tired and without energy. Babies may also show the following signs of breathing problems: 

  • Bluish tone to the skin and lips
  • Grunting
  • Pulling inward of the muscles between the ribs when breathing
  • Rapid breathing
  • Widening of the nostrils with each breath


Often, people who have pneumonia can be successfully treated and do not have complications. Complications from pneumonia are more common in children, older adults, and people with other serious diseases.

This video describes complications that can happen from pneumonia. Read below for a more complete list of possible complications. Medical Animation Copyright © 2020 Nucleus Medical Media Inc. All rights reserved.

Complications of pneumonia that may be life-threatening include:

  • Acute respiratory distress (ARDS) and respiratory failure, which are common complications of serious pneumonia.
  • Kidney, liver, and heart damage, which happens when these organs don’t get enough oxygen to work properly or when your immune system responds negatively to the infection.
  • Necrotizing pneumonia, a condition that develops when your infection causes your lung tissue to die and form lung abscesses (pockets of tissue filled with pus). It also makes your pneumonia harder to treat. You may need surgery or drainage with a needle to remove the pus.
  • Pleural disorders. The tissues that cover the outside of your lungs may become inflamed, and the chest cavity around your lungs may fill with fluid and pus.
  • Sepsis, which happens when bacteria from your lungs gets into your blood and causes inflammation throughout your body.

Diagnosis - Pneumonia

Your doctor will diagnose pneumonia based on your medical history, a physical exam, and test results. Sometimes pneumonia is hard to diagnose because your symptoms may be the same as a cold or flu. You may not realize that your condition is more serious until it lasts longer than these other conditions. 

Medical history and physical exam

Your doctor will ask about your signs and symptoms and when they began. Your doctor will also ask whether you have any risk factors for pneumonia. Your doctor also may ask about: 

  • Exposure to sick people at home, school, or work or in a hospital
  • Flu or pneumonia vaccinations
  • Medicines you take
  • Past and current medical conditions and whether any have gotten worse recently
  • Recent travel
  • Exposure to birds and other animals
  • Smoking

During your physical exam, your doctor will check your temperature and listen to your lungs with a stethoscope.

Diagnostic tests and procedures

If your doctor thinks you have pneumonia, he or she may do one or more of the following tests.

  • Chest X-ray to look for inflammation in your lungs. A chest X-ray is often used to diagnose pneumonia.
  • Blood tests, such as a complete blood count (CBC) to see whether your immune system is fighting an infection.
  • Pulse oximetry to measure how much oxygen is in your blood. Pneumonia can keep your lungs from moving enough oxygen into your blood. To measure the levels, a small sensor called a pulse oximeter is attached to your finger or ear.

If you are in the hospital, have serious symptoms, are older, or have other health problems, your doctor may do other tests to diagnose pneumonia.

  • Blood gas test. If you are very sick, your doctor may need to measure your blood oxygen levels using a blood sample from an artery, usually in your wrist. This is called an arterial blood gas test.
  • Sputum test. Your doctor may test a sample of sputum (spit) or mucus from your cough to find out what germ is causing your pneumonia.
  • Blood culture. This test can identify the germ causing your pneumonia and also show whether a bacterial infection has spread to your blood.
  • Polymerase chain reaction (PCR) test. This test quickly checks your blood or sputum sample to find the DNA of germs that cause pneumonia.
  • Bronchoscopy. If your treatment is not working well, your doctor may use this procedure to look inside your airways. During the procedure, your doctor may also collect samples of your lung tissue and fluid from your lungs to help find the cause of your pneumonia.
  • Chest computed tomography (CT) scan. This test can show how much of your lungs are affected by pneumonia. It can also show whether you have complications such as lung abscesses or pleural disorders. A CT scan shows more detail than a chest X-ray.
  • Pleural fluid culture. In this procedure, called thoracentesis, your doctor uses a needle to take a sample of fluid from the pleural space between your lungs and chest wall. The fluid is then tested for bacteria.

Treatment - Pneumonia

Treatment for pneumonia depends on your risk factors and how serious your pneumonia is. Many people who have pneumonia are prescribed medicine and recover at home. You may need to be treated in the hospital or an intensive care unit (ICU) if your pneumonia is serious.


Your doctor may prescribe some of the following medicines to treat your pneumonia at home or at the hospital, depending on how sick you are.

Management at home

If your pneumonia is mild, your doctor may prescribe medicines or suggest over-the-counter medicines to treat it at home.

  • Antibiotics for bacterial pneumonia. Most people begin to feel better after one to three days of antibiotic treatment. However, you should take antibiotics as your doctor prescribes. If you stop too soon, your pneumonia may come back.
  • Antiviral medicine for viral pneumonia. These medicines may not be effective against some viruses that cause pneumonia.
  • Antifungal medicines for fungal pneumonia.
  • Over-the-counter medicines. Your doctor may suggest over-the-counter medicines to treat your fever and muscle pain or help you breathe easier. Talk to your doctor before taking cough or cold medicine.

Management at the hospital

If your pneumonia is serious, you may be treated in a hospital to get antibiotics and fluids through an intravenous (IV) line inserted into your vein and to get oxygen therapy to increase the amount of oxygen in your blood. If your pneumonia is very serious, you may need to be put on a ventilator.


Your healthcare team may need to perform a procedure or surgery to remove seriously infected or damaged parts of your lung. This may help you recover and may prevent your pneumonia from coming back.

Recovering from Pneumonia - Pneumonia

If you are diagnosed with pneumonia, it is important to follow your treatment plan, take steps to help your body recover, monitor your condition, and take steps to prevent your infection from spreading to others.

It may take time to recover from pneumonia. Some people feel better and are able to return to their normal routines in one to two weeks. For others, it can take a month or longer. Most people continue to feel tired for about a month. Talk with your doctor about when you can return to your normal activities. Watch the video below to learn about managing your recovery at home.

This video shows what to expect as you recover from pneumonia and how you can improve your recovery. Medical Animation Copyright © 2020 Nucleus Medical Media Inc. All rights reserved.

Follow your treatment plan

It is important that you take all your medicines as your doctor prescribes. If you are using antibiotics, continue to take the medicine until it is all gone. You may start to feel better before you finish the medicine, but you should continue to take it. If you stop too soon, the bacterial infection and your pneumonia may come back. It may also become resistant to the antibiotic, making treatment more difficult. 

Take steps to help your body recover

The following steps can help your body recover from pneumonia.

  • Choose heart-healthy foods, because good nutrition helps your body recover.
  • Drink plenty of fluids to help you stay hydrated.
  • Don’t drink alcohol or use illegal drugs. Alcohol and illegal drugs weaken your immune system and can raise the risk of complications from pneumonia.
  • Don’t smoke and avoid secondhand smoke. Breathing in smoke can worsen your pneumonia. Visit Smoking and Your Heart and Your Guide to a Healthy Heart. For free help quitting smoking, you may call the National Cancer Institute’s Smoking Quitline at 1-877-44U-QUIT (1-877-448-7848).
  • Get plenty of sleep. Good quality sleep can help your body rest and improve the response of your immune system. For more information on sleep, visit our How Sleep Works health topic.
  • Get light physical activity. Moving around can help you regain your strength and improve your recovery. However, you may still feel short of breath, and activity that is too strenuous may make you dizzy. Talk to your doctor about how much activity is right for you.
  • Sit upright to help you feel more comfortable and breathe more easily.
  • Take a couple of deep breaths several times a day.

Monitor your condition

Ask your doctor when you should schedule follow-up care. If your symptoms have not improved, your doctor may use a chest X-ray to help diagnose other conditions that may be causing your symptoms.

Your doctor may suggest pulmonary rehabilitation to help you breathe better as your lungs recover. You may also need physical therapy to help you regain your strength. Physical activity can help improve your recovery.

Pneumonia can have long-term effects such as depression, and worsening heart and blood vessel diseases. Call your doctor if you develop these conditions, if your symptoms suddenly get worse, or if you have trouble breathing or talking.

Take steps to protect yourself and others

The following steps can help you prevent spreading the infection to others around you.

  • Cover your nose and mouth while coughing or sneezing.
  • Get rid of used tissues right away.
  • Limit contact with family and friends.
  • Wash your hands often, especially after coughing and sneezing.

Some people get pneumonia again and again. Tell your doctor if this happens. Return to Prevention to find more strategies to help prevent pneumonia.

Participate in NHLBI Clinical Trials

We lead or sponsor many studies on pneumonia. See whether you or someone you know is eligible to participate in our clinical trials and observational studies.



Do you or a loved one have pneumonia?

This study will test whether combining two medicines to reduce inflammation of the airway and to keep it open may help prevent respiratory failure in people who have pneumonia. To participate in this study, you must be at least 18 years old and have severe pneumonia with low blood oxygen levels. This study is located in Scottsdale and Tucson, Arizona; Palo Alto, California; Gainesville and Jacksonville, Florida; Baltimore, Maryland; Rochester, Minnesota; New York, New York; Durham, North Carolina; and Philadelphia, Pennsylvania.
View more information about ARrest RESpiraTory Failure From PNEUMONIA.

Do you often cook indoors using a wood or charcoal-burning stove?

Cooking indoors using a stove that runs on wood, charcoal, or other biomass fuels causes air pollution that can increase your risk of pneumonia. This study will test whether using liquefied petroleum gas instead of biomass fuels can reduce indoor air pollution and its complications in women and children. To participate in this study, you must be either pregnant or a woman between 40 and 80 years old living with a younger pregnant relative, and you must mainly use biomass fuels to cook indoors. This study is located in Guatemala, India, Peru, and Rwanda.

More Information