Pneumonia is an infection of the lungs that can be caused by bacteria, viruses, fungi and, less commonly, other organisms. The air sacs may fill with fluid, making breathing harder. Pneumonia can range from mild illness to a serious infection requiring hospital care.
Common symptoms
- Cough, which may be dry or produce mucus
- Fever or chills
- Shortness of breath or rapid breathing
- Chest pain that worsens with breathing or coughing
- Fatigue and weakness
- Reduced appetite
- Nausea, vomiting or diarrhea in some people
Older adults may develop confusion or reduced alertness rather than typical symptoms. Babies and young children may breathe quickly, feed poorly or become unusually sleepy.
Causes
Many different germs can cause pneumonia. Common bacterial causes include Streptococcus pneumoniae and Mycoplasma pneumoniae. Respiratory viruses including influenza, COVID-19 and RSV can also cause pneumonia. The exact cause is not always identified.
Who is at greater risk?
Risk is higher in young children, older adults, people with chronic heart, lung or liver disease, diabetes, weakened immunity, and people who smoke. Serious pneumonia can nevertheless occur at any age.
Diagnosis
A healthcare professional may assess symptoms, breathing rate, temperature, oxygen level and chest sounds. Depending on severity, testing may include a chest X-ray, blood tests, respiratory samples or other investigations.
Treatment
Treatment depends on the cause and severity. Bacterial pneumonia is treated with appropriate antibiotics. Antibiotics do not treat viral pneumonia. Antiviral treatment may be appropriate for certain viral infections, particularly when started early in people at increased risk of severe illness.
Rest, adequate fluids and appropriate treatment for fever or discomfort can support recovery. More severe pneumonia may require hospital treatment with oxygen, intravenous fluids, antibiotics or respiratory support.
If antibiotics have been prescribed, take them exactly as directed. Seek reassessment if symptoms worsen or are not improving as expected.
Recovery
Cough and tiredness can persist after the infection begins to improve, and recovery from severe pneumonia may take several weeks. Activity can usually be increased gradually as breathing and energy improve.
Prevention
Recommended immunizations can lower the risk of pneumonia from several infections. Regular handwashing, covering coughs and sneezes, avoiding cigarette smoke and managing chronic health conditions can also reduce risk.
When to seek urgent help
Seek urgent medical assessment for worsening shortness of breath, persistent chest pain, coughing blood, dehydration, new confusion, marked weakness or symptoms that improve and then become significantly worse.
Use your local emergency medical service for severe breathing difficulty, blue or gray lips or skin, collapse, inability to wake normally, seizures or severe persistent chest pressure. A baby or child who is struggling to breathe, unusually difficult to wake or unable to drink needs immediate assessment.
Related topics
Sources and Further Reading
- CDC: About Pneumonia
- CDC: Pneumonia Prevention and Control
- National Heart, Lung, and Blood Institute: Pneumonia
- MedlinePlus: Pneumonia
Last reviewed: 4 September 2026