Sarcoidosis is a condition that causes tiny collections of immune system cells in any part of the body. These tiny collections form red, swollen lumps called granulomas. Granulomas most commonly occur in the lungs and the lymph nodes of the chest. They also can occur in the eyes, skin, heart and other organs. Experts don't know the exact cause of sarcoidosis, but it's likely a mix of genetic and environmental factors. Some people appear to have gene changes that make them more likely to develop sarcoidosis. The condition may then be triggered by bacteria, viruses, dust or chemicals. Their immune system overreacts to the trigger, causing inflammation that forms granulomas. There is no cure for sarcoidosis, but most people do not need treatment. Sarcoidosis may go away on its own. Other people need treatment to lessen their body's immune system response. Sometimes sarcoidosis can last for years and may cause organ damage.