CF primarily affects the lungs and digestive system.  The CF gene causes normal sticky mucus to change into a thick, sticky substance, clogging the tiny air passages in the lungs and trapping bacteria.  Repeated infections and blockages cause irreversible lung damage that may lead to lung transplants.  People who have CF must have daily chest therapy to combat the build up of mucus in the lungs.  Most must also take digestive enzyme replacement tablets with food and drink to aid digestion as their pancreatic ducts also become clogged by the thick, sticky substance. This can mean taking up to 60 tablets per day.