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Crohn's disease

The exact cause of Crohn's disease is unknown. Most researchers think that it is caused by a combination of factors.

The exact cause of Crohn's disease is unknown. Most researchers think that it is caused by a combination of factors.

These are thought to be:

  • genetics
  • the immune system
  • smoking
  • previous infection
  • environmental factors

There is no evidence to suggest a particular diet can cause Crohn's disease, although changes to your diet can help control certain symptoms and may be recommended by your specialist or dietitian.

Read treating Crohn's disease for more information.


There is evidence to suggest that genetics plays a role in the development of Crohn's disease.

Researchers have identified more than 200 different genes that are more common in people with Crohn's disease than in the general population.

There is also evidence that Crohn's disease can run in families. About 3 in 20 people with the condition have a close relative (mother, father, sister or brother) who also has Crohn's disease. For example, if you have an identical twin with the condition, you have a 70% chance of also developing it.

The fact that Crohn's disease is more common in some ethnic groups than in others also suggests that genetics plays an important role.

The immune system

The immune system provides protection against harmful bacteria that could potentially find their way into the digestive system.

The digestive system is also home to many different types of so-called "friendly bacteria" that help digest food. The immune system usually recognises these bacteria and lets them do their job without attacking them.

However, in Crohn's disease it seems that something disrupts the immune system, which sends a special protein known as tumour necrosis factor-alpha (TNF-alpha) to kill all bacteria, regardless of whether they are friendly or not. This causes most of the inflammation associated with Crohn's disease.

Previous infection

In certain genetically susceptible individuals, a previous childhood infection may lead to an abnormal immune response, causing the symptoms of Crohn's disease.

One possible source of this infection is a bacterium called Mycobacterium avium subspecies paratuberculosis (MAP). MAP is commonly found in cows, sheep and goats.

Research has found that people with Crohn's disease are seven times more likely to have traces of MAP in their blood compared with the general population.

MAP has been known to survive the pasteurisation process (where milk is treated with heat to kill bacteria), so it is possible that people have become infected with MAP by drinking milk from contaminated animals.

However, the exact role that MAP may play in the development of Crohn's disease is uncertain and some researchers dispute this theory.


Aside from family history and ethnic background, smoking is the most important risk factor for Crohn's disease. Smokers are twice as likely to develop the condition compared with non-smokers.

Furthermore, people with Crohn's disease who smoke usually experience more severe symptoms compared with those who have the condition but do not smoke.

Read more about how to get help to stop smoking.

Environmental factors

There are two unusual aspects of Crohn's disease that have led many researchers to believe that environmental factors may play a part. These are explained below:

  • Crohn's disease is a "disease of the rich". The highest number of cases occurs in developed parts of the world, such as the UK and the US, and the lowest number occur in developing parts of the world, such as Africa and Asia.
  • Crohn's disease became much more widespread from the 1950s onwards.

This suggests that there is something associated with modern Western lifestyles that increases a person's risk of developing the condition.

One theory to explain this is known as the hygiene hypothesis. It suggests that as children grow up in increasingly germ-free environments, their immune system does not fully develop because of a lack of exposure to childhood infections. However, there is little in the way of hard scientific evidence to support this theory.

An alternative theory is the cold-chain hypothesis, which suggests that the increase in the number of cases of Crohn's disease might be linked to the increased use of refrigerators after the Second World War.

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Crohn's disease

A number of different tests may be needed to diagnose Crohn's disease, as it has similar symptoms to several other conditions.

A number of different tests may be needed to diagnose Crohn's disease, as it has similar symptoms to several other conditions.

Initial assessment

During your initial assessment, it is likely that your GP will ask you about the pattern of your symptoms and check whether there may be any contributing causes, such as:

  • diet
  • recent travel – for example, you may have developed travellers' diarrhoea while travelling abroad
  • whether you are taking any medication, including any over-the-counter (OTC) medicines
  • whether you have a family history of Crohn's disease

Your GP may also carry out a series of standard tests to assess your general state of health. For example, they may:

  • check your pulse
  • check your blood pressure
  • measure your weight and height
  • measure your temperature
  • examine your abdomen (tummy)

Blood tests

Your GP may then arrange a series of blood tests. These can be used to assess:

  • the levels of inflammation in your body
  • whether you have an infection 
  • whether you are anaemic (have low levels of red blood cells), which could suggest you are malnourished

Stool sample

You may be asked to provide a stool sample, which can be checked for blood and mucus. It can also be used to determine whether your symptoms are being caused by a parasitic infection such as roundworm, or other infections.

After you have provided a stool and blood sample, you will probably be referred to a gastroenterologist (a specialist in conditions of the digestive system). They will discuss the results with you and carry out the tests described below if they are necessary.


colonoscopy is a test used to examine the inside of your colon. It involves inserting a long flexible tube called an endoscope into your colon through your back passage (rectum).

The endoscope has a light and a camera on the end. The camera can be used to send images to a television screen. These will show the level and extent of inflammation inside your colon.

The endoscope can also be fitted with surgical tools that can be used to take a number of small tissue samples from different sections of your digestive system. This is known as a biopsy. The procedure may feel uncomfortable, but it is not painful.

These tissue samples will be examined under a microscope for the cell changes known to occur in cases of Crohn's disease.

Wireless capsule endoscopy

A wireless capsule endoscopy is a new type of test that involves swallowing a small capsule (about the size of a large vitamin tablet). The capsule works its way down to your small intestines, where it transmits images to a recording device worn on a belt or in a small shoulder bag.

A few days after the test, the capsule passes out of your body in a stool. The capsule is disposable so you do not have to worry about retrieving it from your stools.

As this is a relatively new test, availability may be limited. In some cases, MRE or CTE scans may be used instead of capsule endoscopy.

MRE and CTE scans

Scans called magnetic resonance enterography/enteroclysis (MRE) or computerised tomography enterography/enteroclysis (CTE) may be used to examine the small intestine in people with suspected Crohn's disease.

Before having these scans you will either need to drink a harmless liquid called contrast agent (enterography), or contrast agent may be placed through a tube in your nose that leads to your small intestine (enteroclysis). These contrast agents allow your small intestine to show up more clearly during the scans.

During an MRE scan, magnetic fields and radio waves are used to produce detailed images of your small intestines. During CTE scans, several X-rays are taken and assembled by computer to create a detailed image.

These tests are increasingly used instead of a small bowel enema or small bowel follow-through because they allow more detailed examination of the small intestine. MRE scans also avoid any exposure to X-ray radiation.  

Small bowel enema or small bowel follow-through

A small bowel enema (SBE) and small bowel follow-through (SBFT) are two similar tests that have traditionally been used to examine the whole of the inside of the small intestine, usually at the point where it meets the colon. They are sometimes used because only about the last 20cm of the small intestine is usually seen during colonoscopy.

During an SBE/SBFT, a local anaesthetic spray is used to numb the inside of your nose and throat. A tube is passed down your nose and into your throat before being threaded into your small intestine. This can feel unpleasant at first, but most people find that they get used to the sensation after a few minutes.

A harmless liquid called barium is passed down the tube. The barium coats the lining of your small intestines so that they show up clearly on X-ray. A series of X-ray images will then be taken. The images can often highlight the areas of narrowing and inflammation that are caused by Crohn's disease.

After the test, you will be advised to drink plenty of fluid to help wash the barium out of your body. You may notice that your stools look white for the first few days after having an SBE or SBFT. This is perfectly normal and it is nothing to worry about.

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Crohn's disease

There is currently no cure for Crohn's disease, but treatment can help improve the symptoms.

There is currently no cure for Crohn's disease, but treatment can help improve the symptoms.

The main aims of treatment are to:

  • reduce symptoms, known as inducing remission (remission is a period without symptoms)
  • maintain remission

In children, treatment also aims to promote healthy growth and development.

Your treatment will usually be provided by a range of healthcare professionals, including specialist doctors (such as gastroenterologists or surgeons), GPs and specialist nurses.

Reducing symptoms

If you have Crohn's disease and it's causing moderate or severe symptoms, this is known as "active disease". Treatment for active Crohn's disease usually involves medication, but surgery is sometimes the best option.

Initial treatment

In most cases, the first treatment offered is steroid medication (corticosteroids) to reduce the inflammation. Examples of corticosteroids used for Crohn's disease include prednisolone tablets or hydrocortisone injections.

These medications are often effective in reducing the symptoms of Crohn's disease, but they can have significant side effects, such as:

  • weight gain
  • swelling of the face
  • increased vulnerability to infections
  • thinning and weakening of the bones (osteopenia and osteoporosis)

Because of these possible side effects, your dose will be gradually reduced when your symptoms start to improve.

If you prefer, you may be able to choose to have a milder steroid called budesonide, or a type of medication called a 5-aminosalicylate (such as mesalazine), as an alternative initial treatment. These medications have fewer side effects, but they are less effective.

In children or young people where there are concerns about growth and development, a special liquid diet may be recommended as an initial treatment. This is known as an elemental or polymeric diet and it can help reduce inflammation by allowing your digestive system to recover while ensuring that you get all the nutrients you need.

Additional treatment

If your symptoms flare up twice or more during 12 months or return when your steroid dose is reduced, further treatment may be necessary.

In these cases, medicines to suppress your immune system (immunosuppressants) may be combined with your initial medication. Medicines called azathioprine or mercaptopurine are most commonly used.

These medicines aren't suitable for everyone, so a blood test should be carried out to check if you can use them. If they are not suitable, an alternative immunosuppressant medication called methotrexate may be used.

Side effects of these immunosuppressants can include:

  • nausea and vomiting
  • increased vulnerability to infection
  • feeling tired, breathless and weak, which is caused by anaemia (a decrease in the number of red blood cells)
  • liver problems

During the course of medication you will have regular blood tests to check for serious side effects.

The immunosuppressants azathioprine and mercaptopurine are considered safe in pregnancy and breastfeeding. Women can continue to use these drugs when trying to start a family and during pregnancy.

However, methotrexate must not be taken for at least six months before trying for a baby, as this drug is known to cause birth defects. This applies to both men and women. It must also be avoided while you are breastfeeding.

It's important to speak to your doctor if you are planning a pregnancy or if you become pregnant during your course of treatment for Crohn's disease.

Severe Crohn's disease

For people in poor general health with severe symptoms of Crohn's disease, medicines called biological therapies may be used to reduce your symptoms if corticosteroids and immunosuppressants are unsuitable or ineffective.

Biological therapies are a type of powerful immunosuppressant medication created using naturally occurring biological substances, such as antibodies and enzymes.

The two medicines used to treat Crohn's disease in the UK are called infliximab and adalimumab. They work by targeting a protein called tumour necrosis factor-alpha (TNF-alpha), which is believed to be responsible for the inflammation associated with Crohn's disease. Infliximab can be used for children over six years old and adults, but adalimumab should only be used for adults.

Infliximab is given as a drip into a vein in your arm (known as an infusion) in hospital. Adalimumab is given as an injection, and it may be possible for you, a family member or a friend to be taught how to give it so you don't need to visit hospital for every treatment.

Treatment will usually last at least 12 months, unless these drugs stop being effective sooner than this. After this time, your condition will be assessed to determine if further treatment is necessary.

There is a risk of these medicines causing an allergic reaction, which can cause symptoms such as:

  • itchy skin
  • a high temperature
  • joint and muscle pain
  • swelling of the hands or lips
  • problems swallowing

You should seek immediate medical assistance if you experience these symptoms. Reactions can occur immediately after treatment, although they have been known to occur months later, even after treatment stops.


Surgery may be recommended to reduce your symptoms if your healthcare team feel the benefits outweigh the risks.

In many cases, a type of surgery called a resection is used. This involves removing the inflamed area of the intestine and stitching the healthy sections together.

In some cases, your doctor may recommend a procedure called an ileostomy to temporarily divert digestive waste away from the inflamed colon (large intestine) to give it a chance to heal.

During this operation, the end of the small intestine (the ileum) is disconnected from the colon and re-routed through a hole made in the abdomen, which is known as a stoma. An external bag is attached to the opening to collect waste products.

Once the colon has sufficiently recovered – usually after several months – a second operation will be needed to close the stoma and re-attach the small intestine to the colon.

Maintaining remission

Remission is a period when you don't have any symptoms or your symptoms are mild. During these periods, you can choose whether or not to use medication to help maintain this.

If you decide not to have further treatment, you should be advised about attending regular follow-up appointments and which symptoms to look out for. These symptoms include unintended weight loss, abdominal pain and diarrhoea.

If you choose treatment, this will usually involve immunosuppressants. Corticosteroids are not recommended for maintaining remission.


If you develop complications of Crohn's disease, such as fistulas (channels that develop between two sections of the digestive system) or intestinal narrowing (stricture), these will also need to be treated. Surgery will be necessary in most of these cases. 

See complications of Crohn's disease for more information about this.

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Crohn's disease

Author William Fiennes has lived with Crohn's disease since he was a teenager.

Author William Fiennes has lived with Crohn's disease since he was a teenager. Despite debilitating symptoms, he has written two bestselling books and co-founded the charity First Story, which promotes writing in secondary schools. He reflects on his experience of the disease and how it affects him now.

"I first knew something was wrong when I was 18 years old. I was having a year out in Brazil working as a teacher, and started getting unexplained abdominal pain and persistent diarrhoea.

"I was reluctant to talk about it or seek help, so I didn't see a GP until about six months later, when I was back in England. It was then that I was diagnosed with Crohn's disease. The treatment options around that time were quite limited. There were no biologics and I was put straight on steroid medication.

"Being on steroid medication during my time at university wasn't easy. The side effects were unpredictable and really affected my emotions. Sometimes they gave me a boost and I was full of energy, and sometimes I felt very low. Also, although steroids can be incredibly effective and helpful, they only keep you in remission for so long. As soon as I came off them, the symptoms would return.

"I started pretty much every other kind of treatment that was available, including complementary medicines, and tried changing my diet, but nothing really got to the symptoms.

"This cycle of flare-ups and remission continued for the next few years until, at the age of 24, I was offered the option of surgery. I had a loop ileostomy, where the surgeon diverts your bowel to a stoma to give your colon (the part of my bowel affected by Crohn's) a chance to rest.

"I lived with a bag for 18 months. It was not an easy time. After that, they reversed the surgery and my colon was reconnected.

"I felt pretty good for the following year, before my symptoms returned."

Living with the condition now

"At the moment, I feel pretty stable. I'm currently taking a mixture of infliximab (one of the biologics) and an immunosuppressant called 6-MP (mercaptopurine). This combination therapy is effective and the big advantage for me is that I can avoid steroids. I've been taking 6-MP for the past year and am so glad I decided to go on it.

"If I'm in remission, I can eat pretty much anything, although there are certain foods that I avoid because they make me feel uncomfortable. If I'm having a relapse, everything is hypersensitive.

"Crohn's disease does interfere a lot with my work. It's very hard to write a book when you've got constant pain in your abdomen and you're running to the bathroom all the time.

"When I'm not writing, I'm teaching and helping to run First Story. I also like to run, swim and play cricket. But if I'm in a bad state, it's incredibly hard to do those things. It can be hard to muster up the strength, and I just want to flop and lie down.

"Crohn's disease grinds on and on. It zaps you of vigour and energy – both physically and psychologically.


"Crohn's is a hard condition for people to understand. Everyone's familiar with diarrhoea, but normally for only 24 hours. What they've somehow got to imagine is diarrhoea for 24 hours every day for months with pain and weakness.

"Also, people make the assumption (as Crohn's is a bowel condition) that it's to do with food allergy and you can just cut out certain foods like dairy or wheat and that will solve everything. While this might be helpful in some patients to an extent, it's not in any way a treatment for such an organic disease.

"I'm not sure why I developed Crohn's disease. I've never been a smoker and no-one in my family has it. It's possible that I had a genetic predisposition and the disease was triggered by the bacteria and viruses I was constantly exposed to in Brazil, where I first started getting symptoms."

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Crohn's disease

Read Joseph Barr's story of being diagnosed with Crohn's disease and find out how he manages the condition.

Joseph Barr talks about managing Crohn's disease with medication and how he can still play the sports he loves.

"I had diarrhoea, weight loss and I was unable to keep my food down. I threw up three or four times a day. Eventually, I ended up in hospital for two weeks, where doctors carried out tests, including stomach X-rays, a colonoscopy and a barium meal test.  

"For the barium meal test, I had to swallow a liquid and 20 minutes later my stomach was X-rayed. Under the X-ray, the liquid highlights everything that's going on in the stomach.

"A colonoscopy isn't the greatest experience. A camera is attached to a microscope and inserted into the back passage. It goes quite far up into the colon and everything is recorded on video, which I was able to watch on a screen beside me. 

"I was finally diagnosed with Crohn's disease, an inflammatory disease of the gut. It affects the small and large intestine and can lead to internal bleeding.  

"Initially I was given steroids. It made a big difference straight away and reduced the inflammation a lot. I now take anti-inflammatory drugs every day, and I'll have to take them for the rest of my life. There's no cure for Crohn's disease, so the treatment I've been given helps me manage my condition. My life is now back on track. 

"I still do a lot of the things that I used to do. I still go out with my friends, I can drink alcohol and I don't need to avoid any types of food. I'm still quite active. I can play football and cricket, and I go to the gym as often as I can."

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