How tiny hairs on cells lining the airway sweep mucus up and out of the airway.
A watery layer of mucus lines the airways. The mucus traps any dust and bugs we breathe in. Tiny hairs called cilia move the mucus out of the airway. This is called mucociliary clearance.
In cystic fibrosis, the mucus is thick and sticky. The tiny hairs struggle to move this mucus out of the airway. People with cystic fibrosis often cough up the mucus instead, during chest exercises and physiotherapy.