
Pneumonia is an illness where either one or both of the tissue of the lungs swell, and the air sacs within the lungs begin to fill with mucus. It is most commonly caused by bacteria and viruses. In other cases, it can be caused by fungi or even an inhaled particle of food, in some rare cases. That doesn’t make them all contagious, though. Here is a breakdown of what pneumonia is, and whether or not it is contagious.