Sarcoidosis is a disease of unknown cause that leads to inflammation. It can affect various organs in the body. Normally, your immune system defends your body against foreign or harmful substances. For example, it sends special cells to protect organs that are in danger. These cells release chemicals that recruit other cells to isolate and destroy the harmful substance. Inflammation occurs during this process. Once the harmful substance is destroyed, the cells and the inflammation go away. In people who have sarcoidosis, the inflammation doesn't go away. Instead, some of the immune system cells cluster to form lumps called granulomas in various organs in your body.