Cystic fibrosis is a disease that causes mucus in the body to become thick and sticky. This glue-like mucus builds up and causes problems in many of the body's organs, especially the lungs and the pancreas. People who have cystic fibrosis can have serious breathing problems and lung disease. They can also have problems with nutrition, digestion, growth, and development. There is no cure for cystic fibrosis and the disease generally gets worse over time.