Your donation will make a difference:
Cystic Fibrosis Trust
  • Home
  • /
  • What is cystic fibrosis?

What is cystic fibrosis?

Cystic fibrosis (CF) is a genetic condition affecting more than 10,400 people in the UK. You are born with CF and cannot catch it later in life, but one in 25 of us carries the faulty gene that causes it, usually without knowing.

The gene affected by CF controls the movement of salt and water in and out of cells. People with cystic fibrosis experience a build-up of thick sticky mucus in the lungs, digestive system and other organs, causing a wide range of challenging symptoms affecting the entire body. Read on for more details and links to relevant information, watch our what is CF video below or examine our new interactive body!

Genetics and diagnosis

To have CF,  you need to have inherited two faulty copies of the gene (one from each parent), and as there are many different gene mutations that cause cystic fibrosis, each person with the condition can have very different symptoms depending on the two genes they carry. While people with CF often look healthy on the outside, each individual is battling their own range of symptoms on a daily basis. 1 in 25 people in the UK carry the CF gene, and carrier testing can tell you whether you or your partner is a carrier of the defective gene that causes cystic fibrosis.

Find out more about genetics and diagnosis.

The lungs

The build-up of mucus in the lungs causes chronic infections, meaning that people with cystic fibrosis struggle with reduced lung function and have to spend hours doing physiotherapy and taking nebulised treatments each day. Exacerbations (a sudden worsening of health, often owing to infection) can lead to frequent hospitalisation for weeks at a time, interfering with work and home life.

We are funding a number of different areas of research into the lungs, including investigating infections like Mycobacterium abscessus and Pseudomonas aeruginosa.

Find out more about how cystic fibrosis affects the lungs.

The digestive system

Cystic fibrosis can cause the pancreas to become blocked with mucus, and when this happens enzymes required for digesting food cannot reach the stomach. People with CF often need to take more than 50 tablets a day to help digest food and keep respiratory symptoms in check.

We are funding research into the digestive system, including investigating how to restore fluidity in the gut in people with cystic fibrosis.

Find out more about how CF affects the digestive system.

Additional complications

Men with cystic fibrosis are usually infertile, and pregnancy can place a lot of stress on the body of a woman with cystic fibrosis. Our resource on fertility and pregnancy explains this in more detail. Other complications can include CF-related diabetes, bowel obstructions in babies and bone disease, among others.

Find out more about the additional complications of cystic fibrosis, take a look at our frequently asked questions, or get in touch with our helpline.


One of the most striking features of cystic fibrosis is cross-infection – the risk that people with cystic fibrosis pose to each other. Two people with the condition should never meet face-to-face, as their lungs will harbour specific bugs/infections that could cause a serious infection in someone else with the condition. The risks associated with cross-infection mean that strict segregation should always be in place at CF clinics.

Read our cross-infection policy.


Find out all about diagnosis (newborn or later in life) and what support and resources are available to help you make sense of it all.

Find the answers


Find out more about the treatments and medications to help manage the symptoms of cystic fibrosis.

Read on

Find support

There's loads of support available for people with cystic fibrosis and their families, from grants to help with taking your medication abroad.

Discover more


Public awareness of cystic fibrosis is low; here's your chance to find out the answers to the most commonly asked questions and discover further resources.

Find the answers