What is pneumonia?
Pneumonia is an infection of the lungs. Your lungs have 2 main parts: airways (also called bronchial tubes) and alveoli (also called air sacs). When you breathe, the air moves down through your airways and into your alveoli (say: “al-vee-oh-lie”). From the alveoli, oxygen goes into your blood while carbon dioxide moves out of your blood. When you have pneumonia, your alveoli get inflamed (irritated and swollen) and fill with fluid. This makes it difficult for you to breathe. Pneumonia is usually caused by bacteria or a virus. It can also be caused by fungi or irritants that you breathe into your lungs.