What is the most common cause of pneumonia?

Bacterial infections are indeed the most common cause of pneumonia, particularly in adults. When discussing pneumonia, it is essential to recognize that while viral infections can also cause pneumonia, they typically result in milder illness compared to bacterial pneumonia. Bacteria such as Streptococcus pneumoniae are well-known culprits and often lead to severe symptoms that necessitate medical intervention.

In addition to this, fungal infections can cause pneumonia, but they represent a much smaller minority of cases, primarily affecting individuals with compromised immune systems. Allergens are not a recognized cause of pneumonia; rather, they might lead to respiratory symptoms or conditions such as asthma or allergic bronchitis but don't contribute to the infectious process of pneumonia.

Overall, bacterial pneumonia is prevalent due to factors such as the ability of certain bacteria to colonize the upper respiratory tract and trigger a significant immune response when they invade the lower respiratory tract.