Airways in cystic fibrosis. Computer illustration comparing the airways of a healthy person (top) to that of a person with cystic fibrosis (CF, bottom), where the affected airways are dilated and clogged with mucous (beige) containing traces of blood and bacteria. CF is a hereditary disease affecting the lungs, sweat glands and digestive system that causes both the lungs and pancreas to produce abnormally thick mucous. The mucous in the lungs encourages bacterial growth, leading to severe respiratory infections. The mucous in the pancreas blocks the release of digestive enzymes, resulting in malabsorption. CF is diagnosed by excessive amounts of salt in a person's sweat or by genetic testing.