What is the most common cause of pneumonia?

Pneumonia develops when germs reach the lower airways and the lung tissue reacts with inflammation and fluid. Bacterial pneumonia may follow a respiratory infection, while viral pneumonia can occur with illnesses such as influenza or COVID-19. Cough, fever, chills, breathlessness, chest discomfort and coughing up phlegm can occur, but not everyone has every symptom. The cause cannot be identified reliably from symptoms alone; a clinician may use an examination, oxygen check and selected tests.

Arrange medical assessment when fever, cough or breathlessness is significant, worsening or affecting normal activity. Rest, take fluids if you can, and use only medicines that are suitable for you. Antibiotics help some bacterial infections but do not treat viral pneumonia. Follow prescribed treatment closely and avoid smoking. People with long-term lung or heart disease, weakened immunity, or frailty may need earlier review.

Seek emergency help for severe difficulty breathing, blue or grey lips, confusion, fainting, severe chest pain, or inability to stay awake. Urgent assessment is also needed if symptoms rapidly worsen, fluids cannot be kept down, or a person becomes unusually cold, clammy or very unwell, because pneumonia can sometimes lead to sepsis.

Ask whether the illness is more consistent with bacteria or a virus, whether oxygen or chest imaging is needed, which treatment is appropriate, and what worsening signs should trigger urgent help.