Illustration of a bronchiole in the lungs blocked by excessive mucus (yellow) due to cystic fibrosis (CF). CF is a hereditary disease affecting the lungs, sweat glands and digestive system that causes both the lungs and pancreas to produce abPhotographyrmally thick mucus. The mucous in the lungs encourages bacterial growth, leading to severe respiratory infections. The mucus in the pancreas blocks the release of digestive enzymes, resulting in malabsorption. CF is diagPhotographysed by excessive amounts of salt in a persons sweat or by genetic testing.