Sarcoidosis is a disease caused by small areas of inflammation. It can affect any part of the body but is most common in the lungs—called pulmonary sarcoidosis. In pulmonary sarcoidosis, small patches of inflamed cells can appear on the lungs' small air sacs (alveoli), breathing tubes (bronchioles) or lymph nodes. The lungs can become stiff and may not be able to hold as much air as healthy lungs. In serious cases, sarcoidosis can cause scar tissue in the lungs, which can affect the lungs' ability to move oxygen into the bloodstream.

No one knows what causes sarcoidosis. The good news is that is it usually temporary. In half the cases, sarcoidosis heals naturally—without any treatment. In serious cases, healthcare providers may treat a patient's symptoms to help improve how well the lungs and other organs are working.