👉 Pneumonitis is a medical condition that occurs when the air sacs in the lungs become inflamed. This can cause inflammation and swelling, leading to breathing difficulties and sometimes even death if left untreated. It's also known as pneumonia due to its association with the bacteria that causes it. Pneumonia is a very serious illness that requires immediate treatment. If you have symptoms of pneumonitis, such as chest pain or difficulty breathing, immediately seek medical attention from a healthcare provider.