Cystic fibrosis

What is cystic fibrosis?

Cystic fibrosis (CF) is a genetic condition that you are born with. People with cystic fibrosis cannot control the movement of salt and water between cells in the body. This causes sticky mucus to build up in the lungs and digestive system.

What causes cystic fibrosis?

Cystic fibrosis is caused by faulty genes. People with cystic fibrosis have a problem with the genes that control the movement of salt and water in and out of the cells.

Genes are instructions that tell the body how to grow. Genes come in pairs: everyone gets one set from their mother and one set from their father.

For a child to have cystic fibrosis, both their parents must carry the faulty gene. A child will only have CF if they inherit 2 faulty genes – 1 from their mother and 1 from their father.

Parents don’t always have cystic fibrosis themselves, but they can be carriers of the faulty gene. This means they have 1 faulty gene and 1 normal gene. You need two faulty genes to have cystic fibrosis, so people with only 1 faulty gene have no symptoms. About 1 in 25 of us may carry the gene without knowing it.

If both parents carry the faulty gene, there is a 1 in 4 chance their child will have cystic fibrosis.


How does cystic fibrosis affect the body?

The sticky mucus in the lungs is difficult to clear and can easily get infected.  This means that people with cystic fibrosis get lots of lung infections.

Mucus can also block parts of the digestive system. This can affect how food travels through the gut and how it’s broken down and absorbed. Children with CF will struggle to digest and absorb nutrients from food. They may have problems putting on weight and growing.

Boys with cystic fibrosis usually grow up to be infertile. The tube that carries sperm from their testes to their penis is usually blocked or not there at all. But some men with CF have been able to father children using IVF.


What are the symptoms of cystic fibrosis?

Cystic fibrosis is usually detected from the blood spot test when your baby is 5 days old. That means the diagnosis is often made before symptoms develop.

Some babies with CF may have serious constipation in the first few days of life.  

If untreated, the symptoms of cystic fibrosis usually start in early childhood. These are caused by a build-up of mucus in the lungs and the digestive system.

Treatment to help manage the symptoms will start as soon as the diagnosis is made. If it is not detected, you may see more of these symptoms.

  • Symptoms of cystic fibrosis affecting the lungs
  • Symptoms of cystic fibrosis affecting the digestive system
  • Complications of cystic fibrosis

Cystic fibrosis symptoms that affect the lungs

Common symptoms include:

  • recurrent chest infections
  • persistent wet cough
  • wheezing and shortness of breath

Though the lungs are likely to be normal and healthy at birth, repeated lung infections can damage them. Infections make the airways inflamed, which makes them wider than normal. This is called bronchiectasis.

Cystic fibrosis symptoms that affect the digestive system

If CF is untreated, children may have symptoms affecting the digestive system. These include:

  • difficulty putting on weight and growing
  • pale, greasy poo
  • constipation

Complications of cystic fibrosis

People with cystic fibrosis can experience complications.

Most men with cystic fibrosis will be infertile, and CF can also lead to reduced fertility in women.

People sometimes develop other conditions as a result of cystic fibrosis. This usually happens towards the end of childhood, or in adulthood. These include:

  • diabetes
  • bone disease, causing thin, weakened bones
  • liver problems

Next: how is cystic fibrosis diagnosed?

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Last medically reviewed: September 2019. Due for review: September 2022

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.