When caught early, pneumonia is often treatable and resolves with few problems. However, if left untreated, it can cause complications like:
Blood infection (sepsis or bacteremia). The bacteria that cause bacterial pneumonia can get into your bloodstream. This is known as bacteremia, and it can be life-threatening. You may go into septic shock, a condition in which your blood pressure drops rapidly, making it hard for your organs to get enough oxygen. The bacteria may also spread to other organs and cause other dangerous infections.
Difficulty breathing. If you develop severe pneumonia, breathing may become so difficult that your body doesn’t get enough oxygen. You may need to be hospitalized and put on a ventilator, a machine that pumps oxygen into your body.
Lung abscess. An abscess is a collection of pus. Pneumonia can cause an abscess to form in a cavity in your lungs. If left untreated, an abscess can be life-threatening. You will likely need antibiotics, and you may even need to have the abscess surgically drained.
Pleural effusion. Your lungs are surrounded by two layers of tissue called the pleural membranes. These membranes help your lungs expand smoothly in your chest. However, if you have untreated pneumonia, these membranes can become swollen, and fluid will start to accumulate between them. This is called pleural effusion, and if the fluid becomes infected, it will have to be surgically drained.