Sarcoidosis is a rare disease caused by inflammation. It usually occurs in the lungs and lymph nodes, but it can occur in almost any organ. Sarcoidosis in the lungs is called pulmonary sarcoidosis. It causes small lumps of inflammatory cells in the lungs. The cause of pulmonary sarcoidosis is unknown. Experts think that bacteria, viruses, or chemicals might trigger the disease. It may also be genetic. This means a person is more likely to develop sarcoidosis if someone his or her close family has it.