What Is Cystic Fibrosis?

Cystic fibrosis is a genetic disorder that causes the lungs and digestive system to become clogged with thick mucus. Even though there is no cure for this genetic condition, thanks to breakthroughs in medicines, physical therapy and other treatments, people with cystic fibrosis are living healthier and longer than before. 

Cystic fibrosis (CF) is a genetic disorder that causes the lungs and digestive system to become clogged with thick mucus. The gene called CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) gene that is affected by CF controls the movement of salt and water in and out of cells. People with CF have a buildup of mucus in their lungs, digestive system, and other organs, causing a range of symptoms that affect the entire body.

Symptoms of cystic fibrosis depend on the organ affected and the severity of the disease. People with cystic fibrosis often eat poorly because they have difficulty absorbing nutrients from food. This can slow growth. Want to know more about cystic fibrosis? Scroll down to know the causes, diagnosis and treatment for cystic fibrosis.


Cystic fibrosis (CF) is a genetic disorder in which mucus builds up in the lungs and digestive system leading to lung infections and digestive problems. Symptoms usually begin before the child turns one and varies from child to child but as the lung and digestive damage progress, the condition slowly worsens over time. There are treatments to ease it, but unfortunately, life expectancy is shorter than for other children.1 However, according to the Cystic Fibrosis Trust appropriate health care can help patients live longer and healthier lives. 

The mucus is a slippery lining protecting the airways, gastrointestinal tract, and other organs and tissues. Patients with cystic fibrosis produce thick mucus, which can build up and cause blockage, damage, or infection to affected organs. Inflammation also damages organs such as the lungs and pancreas. Over time, your lungs may not function properly. Mucus also clogs the pancreas (an organ that aids digestion). This means that most people with cystic fibrosis are not properly absorbing nutrients from food and need to eat more calories to avoid malnutrition.2,3 

Causes of cystic fibrosis

In cystic fibrosis, a defect (mutation) in the CFTR gene affects the protein that controls salt movement in and out of cells.3 If the protein is not functioning properly, it cannot transport the chloride component of salt to the surface of the cell.3 Without chlorides to attract water to cell surfaces, mucus in various organs becomes thick and sticky.  

Cystic fibrosis is a highly complex disease that affects people in many ways. For some,  their digestive system is affected more than their lungs while others have problems in their pancreas. 

People with CF inherit two copies of the defective CF gene, one from each parent..1,3=A person inheriting  a defective CF gene from one parent and a normal CF gene from the other parent becomes a carrier and does not have the disease. Whenever two CF carriers conceive a child, the chances are1,3

  • 25% (1 in 4) of children will have CF
  • 50% (1 in 2) of children will be carriers but will not have CF
  • 25% (1 in 4) of children are non-carriers and do not have CF

There are over 1,700 known mutations in this disease.5 Most genetic tests look for only the most common CF mutations.5 Therefore, test results may fail to identify a person who is a carrier. People are born with cystic fibrosis so cannot "catch" it from someone else who has cystic fibrosis.1 

Signs and symptoms of cystic fibrosis

This depends on the organ affected and the severity of the disease. Most people with cystic fibrosis have noticeable symptoms. Furthermore, symptoms can change over time.6 This condition most commonly affects the lungs. In people with cystic fibrosis, the lungs produce thicker-than-normal sputum (phlegm), which can trap bacteria in small airways and cause infection. In addition, typical symptoms include a persistent cough, wheezing, shortness of breath, difficulty breathing and recurrent chest infections.6

Thick mucus secretions interfere with the normal flow of digestive juices from the pancreas, preventing proper digestion or absorption of food, especially fatty foods and fat-soluble vitamins (vitamins A, D, E and K).2,6 This can lead to malnutrition, leading to poor growth and weight gain, bloating and abdominal pain, constipation and persistent diarrhoea.1,2 

Symptoms usually first appear within the first year of life, but in a few cases, they may not appear until later in childhood.

People with CF can experience symptoms such as:

  • skin with a very salty taste
  • persistent cough, sometimes with phlegm
  • frequent lung infections, including pneumonia or bronchitis
  • wheezing or shortness of breath
  • poor growth or weight gain even while having a good appetite 
  • frequent, bulky stools or difficult bowel movements
  • nasal polyps 
  • chronic sinus infections
  • clubbing (enlargement of the fingertips and toes)
  • rectal prolapse
  • male infertility

Management and treatment for cystic fibrosis

There is no cure for cystic fibrosis, but there are many treatments that help control symptoms, prevent or reduce complications, and make living with symptoms easier.4 Various medications may need to be taken to treat and prevent pneumonia.1 Physical activity and the use of airway-clearing techniques may also be recommended to remove mucus from the lungs.2 In addition, people with cystic fibrosis often have to follow a strict daily treatment regimen to stay healthy. It includes taking injections, enzyme tablets to help digest food, and morning and night physical therapy. In severe cases, people may also need a transplant. Lung transplantation is most common because it is usually the organ most affected by cystic fibrosis.1,4 However, some people may have liver, kidney, or pancreas problems. Therefore, transplantation of these organs may be required.1,4


How is cystic fibrosis diagnosed?

Diagnosing cystic fibrosis is a multistep process and should involve the following:

  • newborn screening (for example, in the UK, all newborns are screened for cystic fibrosis with a newborn blood drop test (heel prick test) done soon after birth
  • sweat test - to measure the amount of salt in sweat, which would be abnormally high in people with cystic fibrosis
  • genetic testing or carrier testing - where blood or saliva samples are tested for the faulty gene that causes cystic fibrosis
  • prenatal screening - couples who want children can be tested to see if they are carriers of cystic fibrosis. Genetic testing can be done before or during pregnancy. Mothers are often the first to be tested. However, if you are already pregnant, you and your partner can test together at the same time. If the father has a family history of cystic fibrosis, he can be tested first. Like standard genetic testing, prenatal screening uses a sample of blood, saliva, or cells taken from the inside of the cheek to check for DNA

Most people are diagnosed with CF by the time they are 2 years old, but some are not diagnosed until adulthood. 

How can I prevent cystic fibrosis?

Unfortunately, CF cannot be prevented, but treatment can control symptoms, prevent complications, and make life easier for those with the condition. Treatment has come a long way in recent years and research is ongoing to ensure that everyone with CF can live a long and fulfilling life. 

Who is at risk of cystic fibrosis?

Cystic fibrosis is a genetic disease meaning it runs in families, therefore, people with a CF family history are at risk.

Does cystic fibrosis affect fertility?

Fertility, or the ability to have children, is usually normal or slightly impaired in people assigned female at birth (AFAB) with cystic fibrosis, but most people assigned male at birth (AMAB) with the condition are infertile.7 The reason behind this is the abnormality of the vas deferens (the tube which carries sperm from the testis to the penis).7 The tubes are blocked or may be absent altogether. Although sperm are produced and sexual function remains normal, people AMAB with CF can rarely have children naturally.7

However, recent advances in vitro fertilisation (IVF) and sperm aspiration (extracting sperm directly from the testes) has allowed some people AMAB with cystic fibrosis to have biological children with clinical assistance. Some people AFAB with CF may be advised not to have children if their health is poor, as pregnancy and childbirth could be dangerous to their health. 

How common is cystic fibrosis?

An estimated 105,000 people in 94 countries have been diagnosed with CF and CF affects people of all racial and ethnic groups; 50,000 of them live in Europe.8 Over the past decade, the prognosis has improved significantly, especially since the first small molecules’ market approval treats the underlying defect in CF.8

In total, there are:

  • More than 75% of people with CF are diagnosed by age 2
  • More than half of the CF population is 18 or above 

When should I see a doctor?

Cystic fibrosis can lead to serious complications. Call your healthcare provider if you think you have any of the following:

  • pulmonary exacerbations include worsening pulmonary symptoms such as increased coughing and wheezing, chest congestion, and mucus colour change. People may also have weight loss, anorexia, or fever.
  • coughing and vomiting blood can be signs that an artery has ruptured and is bleeding into the airway. 
  • sudden shortness of breath and chest pain can be signs of pneumothorax or collapsed lungs.  


Cystic fibrosis is a progressive disease that gets worse over time. It can become fatal if it causes a serious infection, or when the lungs stop working properly. Although the outlook for cystic fibrosis has improved significantly in recent years due to advances in treatment, most of those effected have a below-average life expectancy. Regardless, it is crucial for them to consult a GP and adhere to the appropriate treatments. This may increase the chances of a longer and healthier life.  


  1. NHS. (2021, March 16). Cystic fibrosis. NHS choices. Retrieved February 13, 2023. Available from https://www.nhs.uk/conditions/cystic-fibrosis/ 
  2. CF Trust. (n.d.). What is cystic fibrosis? Retrieved February 13, 2023. Available from https://www.cysticfibrosis.org.uk/what-is-cystic-fibrosis
  3. U.S. Department of Health and Human Services. (n.d.). CYSTIC FIBROSIS: Causes. National Heart Lung and Blood Institute. Retrieved February 15, 2023. Available from https://www.nhlbi.nih.gov/health/cystic-fibrosis/causes# 
  4. Asthma + Lung UK. Ways to manage Cystic Fibrosis - British Lung Foundation. (2022, July 25). Retrieved February 13, 2023. Available from https://www.blf.org.uk/support-for-you/cystic-fibrosis/prevention 
  5. Cystic Fibrosis Foundation. (n.d.). About cystic fibrosis. Retrieved February 15, 2023. Available from https://www.cff.org/intro-cf/about-cystic-fibrosis 
  6. U.S. Department of Health and Human Services. (n.d.). Cystic Fibrosis: Symptoms. National Heart Lung and Blood Institute. Retrieved February 15, 2023. Available from https://www.nhlbi.nih.gov/health/cystic-fibrosis/symptoms 
  7. CF Trust. (n.d.). Cystic fibrosis, fertility and fertility treatments. Retrieved February 13, 2023.https://www.cysticfibrosis.org.uk/what-is-cystic-fibrosis/how-does-cystic-fibrosis-affect-the-body/symptoms-of-cystic-fibrosis/fertility 
  8. Bierlaagh, M. C., Muilwijk, D., Beekman, J. M., & van der Ent, C. K. (2021). A new era for people with cystic fibrosis. European Journal of Pediatrics, 180(9), 2731–2739. https://doi.org/10.1007/s00431-021-04168-y
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Karina Silova

MSc Molecular Medicine and BSc Biomedicine, University of East Anglia, UK

My background is in key areas of biomedical research focusing on diseases and their molecular pathways to understand their root cause. I specialise in epigenetics and reproductive health; I am passionate about understanding diseases and helping to bridge the gap between medical science and the general public with accurate and understandable content while educating the public about health and diseases.

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