Which is not a cause of pnomonia?

Pneumonia is primarily caused by infections from bacteria, viruses, or fungi. Non-infectious causes, such as inhaling food, liquids, or irritants like smoke, can lead to a type of pneumonia known as aspiration pneumonia. However, conditions like stress or environmental factors alone are not direct causes of pneumonia. Thus, factors that do not involve pathogens or aspiration are not causes of pneumonia.