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How cystic fibrosis affects the body

Cystic fibrosis (CF) causes the body to produce thick mucus, which affects the lungs and digestive system in particular. Take a look at our interactive body, below, to find out more!

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There are more than 1,400 possible mutations of the faulty gene that causes cystic fibrosis. Everyone living with the condition carries two of these mutated genes, meaning that the way it affects the body can vary wildly from person to person. When you add to this the huge range of other influencing factors, the one thing way can say for sure is that CF is as individual as you are!

Here you can explore some of the most common physical symptoms of cystic fibrosis and find out what may be going on below the surface.


Living with cystic fibrosis means more than just a set of physical symptoms - it can have an impact on your mental and emotional wellbeing. 

Problems with mental health can affect anyone at any time, and everyone with CF experiences their condition differently. Consequently, they may go through particular periods of mental stress, especially if your physical health takes a turn for the worse, while others may find it affects them to a lesser degree. 

If you are concerned that CF may be affecting your mental or emotional health, you can talk to your clinical team.


Cystic fibrosis and other lung conditions can cause the ends of the fingers to swell and become rounder in shape, a condition known as clubbing. The cause of this is unknown.


Nasal polyps are soft swellings that grow in the nose or sinuses. They can vary in size and may grow individually or in a bunch. People with nasal polyps may complain of congestion, sinus pain, a runny nose or a loss of their sense of smell.

Many people with CF suffer with nasal polyps. This is thought to be due to the chronic congestion and infection that CF can cause. Polyps can often be treated with steroids or sometimes with a surgical procedure called a polypectomy. To reduce the chance that the polyps will return after treatment, steroids, antihistamines, antibiotics or sinus flushes may be recommended.

Sinus problems are very common in people with cystic fibrosis.The sinuses are air-filled spaces in the head; three pairs between the eyes and one pair above the eyes. They have a number of functions including warming and humidifying the air we breathe and trapping particles such as bacteria and dust. Cystic fibrosis can cause thick, sticky mucus to build up in the sinuses, resulting in a range of symptoms including facial pain, chronic congestion, loss of smell/taste and a constant need to clear the throat.


Your lungs are responsible for inhaling air and passing the oxygen it contains into the bloodstream, where it is taken to cells that use it to produce energy. Creating energy in the cells produces carbon dioxide, which is transported back to the lungs in the blood stream and then expelled in the air you breathe out.

Air moves around your lungs through airways, which branch into smaller and smaller tubes. You have almost 15,000 miles of airways in your body – that’s like flying from London to New York and back again - twice! At the end of these tubes are tiny balloon-like structures called alveoli, which are surrounded by blood vessels that pick up the oxygen and drop off the carbon dioxide.

Inside your airways there’s a thin layer of mucus that catches anything you breathe in, like bacteria or dust. In people with CF, this mucus is stickier than it should be. This means bacteria can become trapped in the lungs, causing infections.

Your airways are also covered in tiny finger-like structures that move backwards and forwards to push the mucus and everything it contains out of the lungs. These are called cilia, and because the mucus in the lungs of people with CF is stickier, the cilia don’t always work properly.

Physiotherapy helps to loosen the mucus, which in turn helps the movement of air through the lungs.

Digestive system


The pancreas creates enzymes, important chemicals that break down fats, proteins, and carbohydrates in your food. This is important for releasing the nutrients that your body uses to make energy.

In people with CF, the small tubes that transport these enzymes out of the pancreas become blocked with mucus. The enzymes build up in the pancreas instead of reaching the digestive system, causing the pancreas to become inflamed. As a result, people with CF have to take supplements to replace these enzymes with their meals to help digest their food. A person whose pancreas is affected in this way is suffering from ‘pancreatic insufficiency’.

The pancreas also makes insulin, a hormone that regulates the amount of sugar in your blood. The scarring caused by the build-up of enzymes in people with CF can mean that the pancreas does not produce insulin as effectively, resulting in diabetes. This is a common complication of cystic fibrosis.


It is quite common for adults with cystic fibrosis (CF) to have some changes in their liver function, however these changes will often not cause them any difficulties.

It is thought that CF affects the normal secretion and function of bile, which is produced in the liver. The bile can become sticky, causing irritation and inflammation of the bile ducts in the liver. This can be a minor problem for most people with cystic fibrosis. However, occasionally the inflammation leads to permanent damage in the ducts that in turn leads to scarring and problems with the normal functioning of the liver.

It is not known why some people develop CF-related liver damage and others do not.


As we get older our bones become thinner and weaker, and may become more susceptible to fracture. However, in people with CF, thinning of the bones can occur at an earlier age. Bone health is strongly linked to the severity of lung disease and body weight. Over a third of adults with CF have low bone mineral density. Conversely, those with normal weight and height, and good lung function, have near-normal bone density.

Diagram showing how bones of people with cystic fibrosis are affected


In people with CF there is a problem in the transport of salt across cell membranes. This results in a higher concentration of salt in sweat compared with those who do not have the condition. 

Screening for CF is part of the national newborn blood spot screening programme (the heel prick test). The sweat test is performed on babies suspected of having CF, as part of the follow up to the blood spot screening process. This test is safe and painless, and may also be used to help make, or exclude, a diagnosis of CF where there is a family history or a possibility of the condition.

Male puberty and fertility

Young people with CF can experience a delay in the onset of puberty, usually of about 18 months to two years, but sometimes more. This can affect self-esteem and cause anxiety, but is only temporary and should not be cause for concern. Young people with CF will grow and develop the physical appearance of a healthy adult.

Most men with CF (around 98%) will not be able to father a child biologically without assistance from fertility specialists. This is because the tube that carries sperm from the testicles to the penis (called the vas deferens) is either missing or blocked. You may hear this referred to as ‘congenital bilateral absence of the vas deferens’ (CBAVD). The sperm is healthy, there is just no way for it to travel through the vas deferens to become semen. This is called obstructive azoospermia.

It is possible for men with this CF-related problem to father biological children through fertility treatment.

Female puberty and fertility

Young people with CF can experience a delay in the onset of puberty, usually of about 18 months to two years, but sometimes more. This can affect self-esteem and cause anxiety, but is only temporary and should not be cause for concern. Young people with CF will grow and develop the physical appearance of a healthy adult.

Cystic fibrosis can affect female fertility, for a couple of reasons.

Firstly, women with CF are more likely to experience irregular periods or the absence of their period altogether, particularly if ill or very underweight. This means they may not ovulate (produce an egg for fertilisation) each month. Women with CF may also have thicker vaginal mucus, which can make it harder for the sperm to reach the egg.

Many women with CF have babies without undergoing any fertility treatment – if you are not sure whether you want a family right now, it’s best to use contraception until you’ve decided!

People with cystic fibrosis (CF) often look healthy, but it's a life-limiting condition that affects those living with it in many ways. The condition is caused by a genetic mutation that means cells in the human body are unable to move salt and water around effectively. This results in a build-up of thick mucus in the lungs and digestive system, as well as a number of other effects.

People with CF are particularly susceptible to lung infections, and as such have to take precautions to avoid exposure to harmful bacteria and other bugs. For example, two people with the condition should never meet in person, as they are each at risk of cross-infection - passing on harmful bugs to each other.


Cystic fibrosis is as varied as the people who have it - each individual's genotype (genetic make-up) will dictate the symptoms that they experience and how much they will be affected by them. These include poor lung function, frequent and persistent lung infections and the inability to effectively digest food, particularly fats. Additional complications include CF-related diabetes, bone disease and infertility.


There are many treatments available to help ease the effects of cystic fibrosis, and people will take different treatments depending on their symptoms. Treatments range from physiotherapy to reduce the build-up of mucus in the lungs, oral enzymes to help digest the fats in food and antibiotics to treat infections. It is also important to maintain a healthy diet and stay active in order to be in top condition to fight off infections. As lung function can reduce over time, many people will find that they require a double lung transplant.

Treatments have come a long way over the years - take a look at how much progress has been made!

Other effects

Lung infections often require intravenous antibiotics involving long hospital stays away from friends and family, which can also take a toll on the mental health of people with cystic fibrosis. Poor health can also make it hard to maintain employment with regular hours, or go on holiday.

We are dedicated to creating a brighter future for everyone with cystic fibrosis, where they live long and healthy lives unaffected by the condition. Find out more about the research we are funding, our fight for a life unlimited and how you can support us.


Find out more about how cystic fibrosis affects the lungs and the treatments available to fight these symptoms.

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Digestive system

Discover the effects of cystic fibrosis on the digestive system, and how enzymes and other medications can help.

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Other complications

While the lungs and digestive system are the most commonly affected organs, issues like diabetes and bone disease can also occur.

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We fund cutting-edge research into cystic fibrosis, driving forward the process of finding transformational therapies and better treatments to help everyone with cystic fibrosis live a life unlimited by the condition.

Check out our research

Find out more about cystic fibrosis, including stories from inspiring individuals living with the condition in our 'is' magazine and helpful factsheets on a wide range of associated medical and social issues.

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