Pneumonia is a serious lung infection. It causes the air sacs in your lungs to fill with fluid. This can make it very hard to breathe. Pneumonia can be fatal, especially in young children and older adults.

Pneumonia is caused by bacteria, viruses, or fungi. These organisms enter your lungs and begin to multiply. Your body's immune system tries to fight off the infection, but sometimes it's not strong enough. The air sacs fill with fluid, and you develop pneumonia.

Pneumonia can be mild, moderate, or severe. Mild cases may clear up on their own, but more severe cases require hospitalization. Treatment typically involves antibiotics and rest. In some cases, you may need to be on a ventilator to help you breathe.

Pneumonia is serious, but it can be prevented. Getting vaccinated against common respiratory viruses, such as influenza, can help reduce your risk. Washing your hands often and avoiding close contact with people who are sick can also help prevent the spread of pneumonia.