What is the cause for pneumonia?

Infection/inflammati: Pneumonia is a generic term for inflammation of the lung that can be seen on xray. The cause can be infection ( usually viral but often bacterial) or sometimes an inflammatory process. There are too many specific causes to list.

Pneumonia: An inflammatory condition of the tissues of the lung may be caused by infection, drug reactions, tumors, autoimmune conditions and trauma among others.

Almost anything: There are non-infectious causes and infections caused by bacteria, viruses, fungi, parasites, and so on.

Lots of things: Lots of things can cause pneumonia, which is an infection of the lung. Bacteria, viruses & fungi can all cause pneumonia. However, so can aspiration which occurs when choking on something, typically stomach contents. Appropriate vaccines are very useful in decreasing certain, but not all, pneumonias.