Explanation

Cystic fibrosis (CF) is a problem with one of your genes. This gene is on chromosome number 7, and it makes a faulty protein called CFTR. You are born with CF - you cannot catch it from anyone else.

A type of cell called epithelial cells are the ones that are affected by the sick gene. Epithelial cells make up the exocrine glands that line your lungs and digestive system, so CF mostly affects your lungs (your breathing), and your digestive system (your eating).

The faulty CFTR protein means that your exocrine glands cannot balance levels of salt and water like they would normally do. The salt and water build up, making a thick mucous. This is the stuff you cough up.