Pneumonia is a serious infection that makes the tiny air sacs in your lungs fill with fluid or pus, making it hard to breathe. When you have pneumonia, the parts of your lungs that normally fill with air during each breath become clogged, so your body struggles to get the oxygen it needs. This can cause symptoms like coughing, fever, chest pain, and extreme tiredness.

You can get pneumonia from bacteria, viruses, or even fungi. It spreads much like a cold or flu: through coughs, sneezes, or touching contaminated surfaces. While anyone can get pneumonia, it's especially dangerous for very young children, older adults, and those with weakened immune systems.

Before antibiotics were widely used, pneumonia was one of the leading causes of death worldwide. Even today, doctors take it seriously. If someone has pneumonia, they usually need medicine (often antibiotics) and plenty of rest to recover. Vaccines can help prevent some types of pneumonia, which is why doctors recommend them for young children and older adults.

You might hear someone say they were hospitalized with pneumonia, meaning the infection was severe enough to need constant medical care until their lungs could work properly again.