How Cystic Fibrosis Affect the Lungs

Cystic fibrosis causes problems with the lungs

The lungs contain a network of tubes that divide into smaller and smaller tubes as you go deeper inside them. These tubes are called airways. The airways are covered with fine hair-like projections called cilia, which constantly sway back and forth to sweep thin, watery mucus up and out of the airways.1


The airway of a person without cystic fibrosis (CF)

Normally, thin and watery mucus in the lungs traps dirt and germs that might cause an infection. The cilia sweep the mucus out of the lungs and up towards your windpipe, where it is coughed up. This results in the germs being expelled (removed from the body).


Airway of a person without CF

For cilia to be able to sweep mucus out of the lungs, the inside of the airways needs to be moist. This allows the cilia to move back and forth freely.2


Mucus is swept out of the lungs by cilia


The airway of a person with CF

In people with CF, the number and/or function of cystic fibrosis transmembrane conductance regulator (CFTR) proteins are reduced. Learn more about CFTR proteins. CFTR proteins help to make sure we have the correct balance of salt and water in our organs, and when this balance is not right it can result in the production of thick and sticky mucus.3 This makes it difficult for the cilia to move freely and sweep mucus from the lungs.

Cilia are unable to sway freely and sweep mucus from the lungs

If cilia can’t move freely mucus and germs can build up, and this leads to the symptoms of CF. Symptoms of CF include:

  • Wheezing4
  • Shortness of breath4
  • A persistent cough that produces thick phlegm (sputum)4
  • Lung infections (from bacteria such as Pseudomonas aeruginosa, Burkholderia cepacia, and Staphylococcus aureus)5
  • Bronchiectasis6 (damage to the airways that causes them to become wider and makes it harder to move air in and out as a person breathes and harder to clear mucus)

The build-up of mucus and germs can lead to pulmonary exacerbations (PEx). PEx are periods of time when symptoms get worse, and may mean that the lungs aren’t working as well as they used to. During a PEx people may cough more, produce more mucus, notice a change in the colour of their mucus, lose their appetite and experience weight loss.6 In some cases, people suffering from a PEx might need treating with antibiotics and may need to stay in hospital for a few days.6

    1. National Heart, Lung and Blood Institute. The Respiratory System. Available at:

    2. Richardson, M. The physiology of mucus and sputum production in the respiratory system. Nursing Times. 2003; 99(23).

    3. Orenstein DM. Cystic Fibrosis: A Guide for Patient and Family. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2004.

    4. Cystic Fibrosis Foundation. What is cystic fibrosis? Available at:

    5. Rowe SM, Miller S, Sorscher EJ. Cystic Fibrosis. N Engl J Med. 2005; 352(19): 1992–2001.

    6. O'Sullivan B, Freedman S. Cystic fibrosis. Lancet. 2009; 373(9678): 1891–1904.

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