Pneumonia is an infection of the alveoli and lower airways in the lungs that leads to inflammation and fluid accumulation. It can be classified into community-acquired pneumonia and nosocomial pneumonia and is caused by various pathogens, though the cause is sometimes unknown.

The main signs and symptoms of pneumonia include shortness of breath, cough, chest pain, low blood oxygen levels, fever, chills, and fatigue, with variation in different age groups. Younger children may exhibit restlessness and vomiting, and older adults may show less noticeable signs such as disorientation.

Pneumonia is diagnosed through a combination of signs and symptoms, chest imaging, and a clinician's assessment of medical history and physical examination. This process helps differentiate pneumonia from other conditions with similar symptoms to ensure appropriate treatment.

Antibiotics are the primary treatment for most pneumonia cases, and the specific choice depends on individual factors and local data. If the pneumonia is caused by nonbacterial pathogens, antiviral or antifungal medications may be used, whereas severe cases may require additional supportive treatments.

Many supplements have been studied for pneumonia, but there is limited evidence to support their effectiveness; for example, vitamin C and probiotics were found to be ineffective, and zinc may reduce pneumonia risk in children but does not aid recovery when added to antibiotic treatment. Additionally, low vitamin D levels are associated with increased pneumonia risk, but the effect of supplementation remains unclear.

There is limited evidence that diet may influence pneumonia risk; certain foods like coffee, tea, oily fish, and fruit potentially reduce risk, and red meat may increase it. However, for people with pneumonia, meeting their daily nutritional needs is crucial because malnutrition can lead to higher mortality rates, and increasing energy and protein intake may improve outcomes for those hospitalized with severe pneumonia.

Increased physical activity and sauna bathing may reduce the risk of developing pneumonia, and chest physiotherapy is a common treatment for clearing mucus from the airways, though its effectiveness is often questioned in studies.

Pneumonia can be caused by various pathogens, including bacteria (like Streptococcus pneumoniae), viruses (such as influenza and RSV), and fungi (like Pneumocystis jirovecii), and the prevalence of these microbes varies by geography and age group. Additionally, aspiration pneumonia can occur when food, liquids, or gastric contents enter the lungs.