Crohn's disease

Page last reviewed: 13/07/2011

Crohn's disease is a chronic (long-term) condition that causes inflammation of the lining of the digestive system.

Inflammation usually occurs in the ileum (the last section of the small intestine) or the colon (the large intestine). However, inflammation can occur anywhere in the digestive system, from the mouth to the anus (back passage).

Over time, the inflammation that is caused by Crohn's disease can damage sections of the digestive system, causing additional complications, such as narrowing of the colon.

Common symptoms of Crohn's disease include:


The cause of Crohn's disease is unknown. However, research suggests that a combination of environmental and genetic factors is responsible for the onset of Crohn's disease.

How common is Crohn's disease?

Crohn's disease is a rare condition. It is estimated that for every 100,000 people there will be seven new cases of Crohn's disease a year.

Most cases of Crohn's disease first develop in people who are between 16 and 30 years of age, although the condition can affect people of all ages, including children.

Crohn's disease is more common in white people than in black people, or those of Asian descent. The condition is most prevalent among Jewish people of European descent.

Crohn's disease affects slightly more women than men.


The outlook for Crohn's disease is highly variable. People can have long periods of remission that last for weeks or months where they have no, or very mild, symptoms, followed by periods where their symptoms flare up and are particularly troublesome.

There is currently no cure for Crohn's disease. However, medication is available that can be used to treat the symptoms and prevent them from returning.

About 80% of people with Crohn's disease will require surgery to relieve their symptoms, repair damage to their digestive system and treat complications of the condition.

Page last reviewed: 13/07/2011

Common symptoms of Crohn's disease include:

  • recurring diarrhoea
  • abdominal pain and cramping (the pain is usually worse after eating)
  • blood and mucus in your faeces (stools)
  • fatigue
  • weight loss

Weight loss is caused by a combination of factors. For example, inflammation can interfere with your ability to digest food, and the symptoms of pain and diarrhoea can cause a reduction in your appetite.

Less common symptoms of Crohn's disease include:

  • a high temperature (fever) of 38°C (100°F), or above
  • nausea
  • vomiting
  • joint pain and swelling (arthritis)
  • inflammation and irritation of the eyes (uveitis)
  • skin rashes

When to seek medical advice

You should contact your GP if you:

  • experience symptoms of persistent diarrhoea that do not respond to over-the-counter (OTC) medications
  • experience symptoms of persistent abdominal pain
  • experience unexplained weight loss
  • notice blood in your faeces (stools)
Diarrhoea is the passing of frequent watery stools when you go to the toilet.
Stool (also known as faeces) is the solid waste matter that is passed from the body as a bowel movement.
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.
Joints are the connection point between two bones that allow movement.
Loss of appetite
Loss of appetite is when you do not feel hungry or want to eat.

Page last reviewed: 13/07/2011

The exact cause of Crohn's disease is unknown. Most researchers think that the condition could be caused by a combination of the factors listed below.

  • Genetics: genes that you inherit from your parents may increase your risk of developing Crohn's disease.
  • The immune system: it appears that the immune system is responsible for the inflammation that occurs in Crohn's disease.
  • Previous infection: a previous bacterial or viral infection may trigger an abnormal response from the immune system.
  • Environmental factors: the fact that Crohn's disease is most common in westernised countries, such as Ireland, and least common in poorer parts of the world, such as Africa, may be due to environmental factors.

These four factors are discussed below in more detail.


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

The direct evidence is that researchers have indentified 32 different specific genetic alterations (genetic mutations) that are more common in people with Crohn's disease than in the population at large.

The indirect evidence is that Crohn's disease can run in families. If you have a first-degree relative (mother, father, sister or brother) with Crohn's disease, you have a 5-10% risk of developing the condition yourself. And if you have an identical twin with Crohn's disease, you have a 37% risk of developing the condition.

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

The immune system

The immune system plays a complex and demanding role in the digestive system. It provides protection against harmful bacteria that could potentially find their way into the digestive system.

However, the digestive system is also home to more than 500 different types of so-called 'friendly bacteria' that help with the digestion of food. The immune system has to recognise these bacteria and let them do their job without attacking them.

In Crohn's disease, it appears that something disrupts the immune system which sends a special antibody, known as tumour necrosis factor (TNF) to kill all bacteria, regardless of whether they are friendly or not. It is the TNF antibodies that cause most of the inflammation that is associated with Crohn's disease.

Previous infection

A related theory to the two that are outlined above is that in certain genetically susceptible individuals, a previous childhood infection may lead to an abnormal immune response, causing the symptoms of Crohn's disease to occur.

One possible source of this infection is a bacterium called mycobacterium avium subspecies paratuberculosis (MAP). MAP is commonly found in cows, sheep and goats, and it causes a similar disease in animals that is known as Johne's disease.

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 population at large.

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

However, the exact role that MAP may play in the development of Crohn's disease is uncertain.

Environmental factors

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

  • Crohn's disease is a 'disease of the rich'. Rates are highest in developed parts of the world, such as the UK and USA, and lowest in underdeveloped parts of the world, such as Africa and Asia.
  • Crohn's disease became much more widespread from the 1950s onwards. Before the Second World War the condition was rare.

These factors seem to suggest that there is something that is associated with modern, western lifestyles that increases a person's risk of developing Crohn's disease.

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

An alternative theory is known as the cold-chain hypothesis. This theory suggests that the increase in cases of Crohn's disease can be linked to the increased use of refrigerators after the Second World War.

Psychrotrophic bacteria are bacteria that can survive, and sometimes grow, in cold environments. Therefore, as people eat more chilled foods, their exposure to these bacteria increases, and it is these bacteria that cause the abnormal immune response.

Traces of psychrotrophic bacteria have been found in people with Crohn's disease, although, as the researchers behind the cold-chain hypothesis admit, this could be pure coincidence.

Risk factors


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

Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some others are good for you.
Genetic is a term that refers to genes, which are the characteristics inherited from a family member.
Immune system
The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Page last reviewed: 13/07/2011

There is no single test that can be used to confirm or disprove a diagnosis of Crohn's disease.

Therefore, you will have to have a series of tests before a confident diagnosis can be made. This will help rule out other possible causes of your symptoms, such as ulcerative colitis (a condition that causes inflammation of the colon).

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 picked up travellers' diarrhoea' while travelling abroad)
  • whether you are taking any medication, including over-the-counter (OTC) medication
  • whether you have a family history of Crohn's disease

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

  • check your pulse
  • give you blood pressure tests
  • measure your weight and height
  • measure your temperature
  • perform a physical examination of your abdomen

Blood tests

The next stage of the diagnosis is to refer you for a series of blood tests. Blood tests can be used to assess a number of factors including:

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

Stool sample

You may be asked to provide a sample of your faeces (stool) for testing. The stool sample can be checked for the presence of blood and mucus. It can also be used to determine whether your symptoms are being caused by a parasite infection, such as roundworm.


A colonoscopy is a test that is used to examine the inside of your colon. It involves inserting a long flexible tube, known as an endoscope, into your rectum (back passage) and up into your colon. The endoscope has a light and a camera on the end.

The camera relays images to a video screen, allowing the level and extent of inflammation inside your colon to be assessed.

The endoscope can also be fitted with various 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.

The tissue samples that are taken during the biopsy will be examined under a microscope for the distinctive cell changes that are known to occur in cases of Crohn's disease.

Small bowel enema (SBE)

A small bowel enema (SBE) is a test to examine the inside of the small intestine, usually at the point where it meets the colon. This area cannot be seen using a colonoscopy.

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

A liquid, called barium, is then passed down the tube. The barium coats the lining of your small intestines, helping them to show up on X-rays.

A series of X-ray images is then taken. The X-rays can often highlight areas of narrowing and inflammation that have been 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 are whiter than usual for the first few days after having an SBE. This is perfectly normal and it is nothing to worry about.

Further testing

Further testing is only usually required if the results of the above tests are inconclusive, or if it is thought you may have developed complications, such as a blockage in your colon or an abscess (a pus-filled cavity).

Tests that you may have include:

  • a computerised tomography (CT) scan, where several X-rays are taken and then assembled together by computer to create a more detailed image
  • a magnetic resonance imaging (MRI) scan, which uses magnetic field and radio waves to produce detailed images of the inside of your body
  • a wireless capsule endoscopy

A wireless capsule endoscopy is a new type of test. It involves swallowing a small capsule that is about the size of a typical headache tablet. The capsule will work its way down to your small intestines where it will transmit images wirelessly to a computer.

A few days after the test, the capsule will be passed out of your body when you are passing a stool. The capsule is designed to be disposable so you do not have to worry about retrieving it from your stools.

A biopsy is a test that involves taking a small sample of tissue from the body so it can be examined.
An enema is an injection of fluid into the large intestine to empty the bowel. It can also be used to make the bowels show up more clearly in an X-ray.
Stool (also known as faeces) is the solid waste matter that is passed from the body as a bowel movement.
An X-ray is a painless way of producing pictures of inside the body using radiation.

Page last reviewed: 13/07/2011

Your treatment plan

If you are diagnosed with Crohn's disease, your care team will draw up a treatment plan for you. There are three goals in your treatment plan:

  • treat the active disease, in order to resolve your symptoms
  • prevent your symptoms returning with maintenance therapy
  • treat any returning symptoms with relapse therapy


Steroids are a type of hormone medication. Hormones are groups of powerful chemicals that have a wide range of effects on the body. One such effect is to reduce inflammation.

Steroids are usually only used to treat the active disease because their long-term use is associated with a range of adverse side effects.

Budesonide and prednisolone are two steroids that are often used to treat Crohn's disease.


Budesonide is usually the first steroid that is prescribed to help control the symptoms of Crohn's disease.

If you take budesonide on a short-term basis (fewer than 12 weeks) you may experience the following side effects:

  • acne
  • swelling of the face
  • swelling of the hands, arms, feet and legs due to a build-up of fluids (oedema)
  • mood changes, such as feeling irritable or anxious
  • insomnia
  • indigestion

If you take budesonide for more than 12 weeks, you may experience the following side effects:

  • thinning of the bones (osteoporosis)
  • increased vulnerability to infection
  • cataracts (a type of eye condition)
  • muscle cramps and stiffness

If you need to take budesonide for more than 12 weeks, you may be given vitamin D and calcium supplements to help protect against the effects of osteoporosis. Both of these supplements help to strengthen the bone.

Due to your increased vulnerability to infections, you should avoid close contact with people who are known to have infections, particularly those with chickenpox, measles and shingles.

You should not suddenly stop taking budesonide because doing so can cause adverse effects. When you no longer need to take your medication, your dose will be gradually reduced over time.


Prednisolone is used in cases where budesonide proves ineffective, or where your symptoms are moderate to severe.

Prednisolone has the same type of short-term and long-term side effects as budesonide. In addition, prednisolone has been known to cause mental health problems in an estimated 5% of people.

These include:

  • feeling depressed and thinking about suicide
  • feeling very excited and happy
  • experiencing sudden and severe mood changes (happy one minute, very depressed the next)
  • feeling anxious
  • having problems thinking clearly and feeling particularly confused
  • memory loss
  • hallucinations (seeing and hearing things that are not real)

If you experience any of these symptoms, contact your GP as soon as possible because your dose may need to be adjusted.

The advice outlined above about avoiding people with infections and not suddenly stopping your prescribed dose also applies to prednisolone.



Sulfasalazine belongs to a group of medicines called aminosalicylates. Aminosalicylates are known to reduce inflammation inside the colon.

Sulfasalazine can be used as an alternative to steroids to treat mild cases of Crohn's disease.

Depending on exactly where the inflammation is occurring, you may be given sulfasalazine in tablet form or as a suppository. A suppository is a capsule that you insert into your anus (back passage).

Common side effects of sulfasalazine include:

  • headache
  • nausea
  • abdominal pain
  • diarrhoea

If side effects become particularly troublesome, you should tell your GP as the dose used may need to be adjusted.


Immunosuppressants are a type of medication to suppress the activities of the immune system in order to help reduce inflammation on a long-term basis.

Immunosuppressants are used in maintenance therapy and in combination with steroids when a person has a relapse of symptoms.

Two immunosuppressants that are widely used for treating Crohn's disease are azathioprine and mercaptopurine.


Depending on the severity of your symptoms, you may be given azathioprine in tablet form or as an injection.

Common side effects of azathioprine include:

  • increased vulnerability to infection
  • bleeding and bruising more easily

Due to your increased vulnerability to infection, you should avoid people with a known chickenpox or shingles infection.

Less common side effects of azathioprine include:

  • headaches
  • shortness of breath and dizziness when exercising
  • nausea
  • vomiting


Mercaptopurine was originally developed to treat leukaemia (cancer of the blood cells), but it has since proved effective in the treatment of Crohn's disease.

As mercaptopurine is given in tablet form, its side effects are not as severe as those associated with other forms of chemotherapy treatment.

Common side effects of mercaptopurine include:

  • nausea
  • vomiting

Less common side effects of mercaptopurine include:

  • loss of appetite
  • feeling tired, breathless and weak, which is caused by a drop in the number of red blood cells (anaemia)

Mercaptopurine can also temporarily affect the quality of a woman's eggs and a man's sperm, which could increase the risk of birth defects. It is therefore very important to use effective contraception if you are sexually active and you are taking mercaptopurine. 

Biological therapies

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

There are currently two biological therapies licensed for use in England:

  • infliximab
  • adalimumab

Each medication is discussed in more depth below.


Infliximab is usually only recommended in severe cases of Crohn's disease that have not responded to steroid and immunosuppressant treatments, and where the person is unsuitable for surgery.

For example, if a person has had previous surgery to remove a section of bowel, removing more of the bowel could result in a loss of digestive function. Alternatively, a person may be in too poor a state of health to withstand the effects of surgery.

Infliximab works by targeting the tumour necrosis factor (TNF) antibodies that are responsible for much of the inflammation that is associated with Crohn's disease.

Infliximab is given through a drip in your arm over the course of two hours. This is known as an infusion.

Depending on how well your symptoms respond to treatment, you may only require one infusion, or you may have three infusions that are given every eight weeks.

Around one person in four has an allergic reaction to infliximab and experiences symptoms such as:

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

Symptoms can range from mild to severe and they usually develop in the first two hours after the infusion has finished.

However, in a minority of cases, people have experienced a delayed allergic reaction days, or even weeks, after an infusion. If you begin to experience the symptoms listed above after having infliximab, you should seek immediate medical assistance.

Due to the significant risk of having a severe allergic reaction (one in four), your health will be carefully monitored after your first infusion and, if necessary, powerful anti-allergy medication, such as intravenous steroids, may be used.

There have been several cases where infliximab has reactivated a previously dormant tuberculosis (TB) infection. Therefore, it may not be suitable for you if you have a previous history of TB. Infliximab is also not recommended for people with a history of heart disease.

Infliximab will also make you more vulnerable to infection so you should avoid contact with people who have a known chickenpox or shingles infection.

You should report any symptoms of a possible infection, such as coughs, a high temperature or a sore throat, to your GP.


Another biological therapy available for people with severe Crohn's disease is a medication called adalimumab. Adalimumab works in a similar way to infliximab by targeting TNF antibodies.

Adalimumab is given by injection and most people will need to have an injection every two weeks. Your GP or practice nurse will be able to teach you how to administer the injections yourself at home. 

Like infliximab, adalimumab will make you more vulnerable to infection, so if you are taking it you should avoid contact with people with chickenpox or shingles and always report any symptoms of a possible infection to your GP.

Adalimumab can cause reactivation of the hepatitis B virus in people who were previously infected. If you know you have previously been infected with hepatitis B, you should inform your GP because adalimumab may not be suitable for you.

Common side effects of adalimumab include:

  • pain, swelling, redness and itching at the site of the injection
  • headache
  • abdominal (tummy) pain
  • nausea (feeling sick)
  • vomiting (being sick)
  • skin rash
  • muscle, joint and bone pain
  • respiratory tract infections, such as colds, a runny nose and pneumonia (lung infection)


Surgery is often required when the symptoms of Crohn's disease cannot be controlled using medication alone. An estimated 80% of people with Crohn's disease will require surgery at some point in their life.

Surgery cannot cure Crohn's disease, but it can provide long periods of remission, often lasting several years. During surgery, the inflamed section of the digestive system is removed and the remaining part is reattached.

Antibiotics are medicines that can be used to treat infections caused by micro-organisms, usually bacteria or fungi. For example amoxicillin, streptomycin and erythromycin.
Antibodies and immunoglobins are proteins in the blood. They are produced by the immune system to fight against bacteria, viruses and disease.
The anus is the opening at the end of the digestive system where solid waste leaves the body.
Corticosteroid is a naturally occurring hormone produced by the adrenal gland, or a synthetic hormone having similar properties. It is used to reduce inflammation, so reducing swelling and pain.
Dose is a measured quantity of a medicine to be taken at any one time, such as a specified amount of medication.
A drip is used to pass fluid or blood into your bloodstream, through a plastic tube and needle that goes into one of your arteries or veins.
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.
Intravenous (IV) means the injection of blood, drugs or fluids into the bloodstream through a vein.

Page last reviewed: 13/07/2011


While there is no evidence that diet causes, or plays a role in, Crohn's disease, some people with the condition have found that certain foods seem to aggravate their symptoms.

Types of food and drink that have been associated with a worsening of symptoms include:

  • milk
  • alcohol
  • dairy products
  • spicy foods
  • fatty foods
  • high-fibre foods

However, there are no definitive dietary recommendations for Crohn's disease because different people react differently to certain foods.

You may find it useful to keep a food diary in which you note the foods that you eat and record their effects on your symptoms.

Eating six smaller meals a day, rather than three larger meals, may also help improve your symptoms.

Some researchers have suggested that an elimination diet may help control symptoms of Crohn's disease. An elimination diet involves permanently removing entire food types, such as grains or sugars, from your diet.

However, an elimination diet is a controversial approach to treatment and it is not accepted by many experts who are working in the field of Crohn's disease. Therefore, you should not attempt an elimination diet without first consulting your GP.

You may also require vitamin and food supplements if you are unable, or unwilling, to eat certain foods. For example, as dairy products are an important source of calcium, you will require calcium supplements if you are no longer able to eat dairy products. Your GP will be able to advise you about any supplements that may be appropriate for you.

Elemental diet

If you are experiencing particularly severe symptoms, or you are showing signs of malnutrition, your GP may recommend an elemental diet.

An elemental diet is a liquid-only diet where all of your nutritional needs are met by drinking specially prepared liquid meals. These are a bit like the slimming shakes that are used in some diet programmes.

An elemental diet is a useful way of allowing your digestive system to rest while ensuring that you get all the nutrients that you require. In most cases, people only have to stay on an elemental diet on a short- to medium-term basis.

Page last reviewed: 13/07/2011

The two most common complications that are associated with Crohn's disease are:

  • Bowel obstruction: intensive inflammation causes sections of the bowel to narrow and harden, leading to bowel contents becoming stuck in the bowel.
  • Fistula: a fistula is an abnormal channel that develops between two sections of the digestive system.

These complications are discussed in more detail below.

Bowel obstruction

If your bowel becomes obstructed, you will either not be able to pass any stools at all, or you will only be able to pass watery stools because only liquid will be able to get past the point of obstruction.

Other symptoms of bowel obstruction include:

  • abdominal pain and cramping
  • vomiting
  • bloating
  • an uncomfortable feeling of fullness in your abdomen

A bowel obstruction requires immediate medical treatment. Left untreated, there is a risk that the bowel could rupture (split), which can lead to internal bleeding and widespread infection.

If you suspect that you have an obstructed bowel, contact your GP as soon as possible.

If a bowel obstruction is suspected, it is likely that you will be admitted to hospital so that your health can be carefully monitored. In some cases, it may be possible to clear the bowel obstruction by switching you to a liquid-only diet and using medication to reduce inflammation. However, if this does not work, surgery will be required to unblock the bowel.

You may require a temporary colostomy while your bowel heals. A colostomy is an operation where a section of your colon is diverted and attached to an opening in your abdominal wall. The opening is known as a stoma. A pouch is attached to the stoma to collect waste products, such as stools. Once your bowel has healed, the colon can be reattached and the stoma sealed.

If you experience repeated episodes of bowel obstruction, a permanent colostomy may be recommended.


If your digestive system becomes scarred as the result of excessive inflammation, ulcers (open sores) can develop.

Over time, the ulcers can expand into tunnels, or passageways, that can run from one part of the digestive system to the other or, in some cases, to the bladder, anus or skin. These passageways are known as fistulas.

Small fistulas usually cause no symptoms. Larger fistulas can become infected and cause symptoms such as:

  • a constant, throbbing pain
  • a high temperature (fever) of 38°C (100°F) or above
  • blood and/or pus in your faeces (stools)
  • generally feeling very unwell

If a fistula develops on the skin (usually on, or near, the anus) it may release a foul-smelling discharge.

Surgery is usually required to treat a fistula. During surgery, the surgeon will cut open the fistula while you are under general anaesthetic. They will scrape and flush out the contents of the fistula which will be laid open and flattened out.

Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Content provided by NHS Choices and adapted for Ireland by the Health A-Z.

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