Crohn’s Disease

What is Crohn’s disease?

Crohn’s disease is one of the two main forms of inflammatory bowel disease (IBD). The other main form of IBD is ulcerative colitis (UC). Crohn’s disease is believed to be caused by an overactive immune response which results in inflammation within the digestive system. When this inflammation develops, the affected person will typically experience debilitating symptoms, which may include bowel obstructions, nausea, chronic diarrhea and abdominal pain.

Most commonly, the inflammation within the digestive system which occurs in Crohn’s disease affects sections of the terminal ileum ‒ the final segment of the small intestine ‒ and/or the colon ‒ the large intestine ‒ but it can affect any of the gastrointestinal organs.

Crohn’s disease usually develops in adulthood but can, in some cases, manifest in childhood or adolescence.[1] It is a lifelong, chronic condition.

People affected by Crohn’s disease experience periods of:

  • Remission, in which the disease is inactive and the individual is without symptoms
  • Flare-ups, in which the disease is active and symptoms are present

Treatment for Crohn’s disease aims to alleviate the symptoms and prolong periods of remission.


A person who is affected by Crohn’s disease may experience a wide range of symptoms which may also vary in severity.

Common symptoms of Crohn’s disease include:[2]

  • Digestive discomfort: This takes the form of abdominal pain and cramping and often occurs one or two hours after eating, but may occur at any time. People with Crohn’s disease often avoid eating or eat less in order to avoid digestive discomfort, which can lead to weight loss. Digestive discomfort is usually at its worst when an individual is experiencing a flare-up of the disease.[3]

  • Diarrhea: This is one of the main symptoms of Crohn’s disease and happens when the gut cannot absorb all the necessary fluid from food during the digestive process. This often creates a sense of urgency and needing to rush to the toilet.[4]

  • Fatigue: A high percentage of people with Crohn’s disease are affected by fatigue.[5] This may be caused by lack of sleep, which in people with Crohn’s disease is common due to digestive discomfort, high stress levels, depression and using medication of which insomnia and/or discomfort are side effects.[6]
    Fatigue may also be caused by malnutrition which is a common consequence of Crohn’s disease, as the inflammation in the gastrointestinal tract can result in a less efficient uptake of the essential compounds derived from food, which the body needs in order to function properly. People with Crohn’s disease are commonly found to be deficient in iron, vitamin B12 and vitamin D.[7] These deficiencies often correlate to a loss in muscle strength.[8]

  • Blood in one’s stools: Crohn’s disease typically causes bleeding in the lower digestive tract, which manifests as bright red blood in one’s stools. The condition may also cause bleeding in the colon, associated with inflammation, anal fissures and fistulas.[9]

  • Mucus in one’s stools: A healthy intestine produces a certain amount of mucus in order to protect and lubricate the bowel area. When a person is affected by Crohn’s disease, the production of mucus can increase, resulting in surplus mucus emerging with one’s stools. This usually takes the form of a gel-like material which appears to coat the stool.[10]

  • Unintentional weight loss: Due to avoiding certain foods or food groups and failing to absorb sufficient energy from one’s food as a result of malabsorption and diarrhea, people with Crohn’s disease frequently experience weight loss.

Less common symptoms of Crohn’s disease include:[2]

  • Nausea and vomiting
  • High temperature and/or being prone to fevers
  • Swelling and pain in the joints
  • Mouth ulcers
  • Skin irritation involving redness, swelling and itching
  • Uveitis, i.e. red and irritated eyes

Complications from Crohn’s disease

In addition to experiencing the immediate symptoms of Crohn’s disease, people with the condition are also predisposed to further health complications.

Related conditions which commonly affect people with Crohn’s disease include:

  • Intestinal obstruction: This condition is also referred to as bowel obstruction. Over time, the inflammation of the digestive tract in people with Crohn’s disease can cause the wall of the affected area(s) of the small or large intestine to thicken permanently. This can cause the intestine to become blocked. Intestinal obstructions can be fatal if left untreated and often require surgical removal.[11]

  • Anal fissure: This is a tear or sore which can occur in the anal canal. Anal fissures are common in people with Crohn’s disease, due to the trauma which is caused to the area by frequent bowel movements.[12]

  • Anal abscess: An anal abscess is an infected cavity filled with pus. Abscesses can affect the anus or rectum as a result of the internal glands in the anus becoming infected. This is likely to occur in people with Crohn’s disease, as the tissue in this area is often traumatized due to frequent bowel movements.[13]

  • Fistulae: The inflammation caused by Crohn’s disease often creates ulcers, leaks and abscesses in the bowel wall. The more severe the inflammation, the more likely it is that one of these abrasions will develop into a hole, which then forms a fistula. A fistula is a tunnel which forms between two parts of the bowel or between the bowel and the outer skin or between the bowel and other surrounding hollow areas or organs, such as the bladder or vagina, which are not normally connected to the bowel.[14]
    The larger a fistula is, the more likely it is to become infected. This can cause problems like irritation of the skin and leakage of feces into or from the space which has been connected to the bowel.[14]

  • Iron deficiency anaemia: This condition often occurs in people with Crohn’s disease, due to the bleeding in the digestive tract, and because malabsorption can cause a person’s iron levels to become deficient. It is associated with shortness of breath, fatigue and a pale complexion.[15]

  • Osteoporosis: Osteoporosis is a disorder of the skeleton, in which the structure of the bones becomes porous. This can lead to the bones becoming weak, fragile and prone to painful fractures (breaks). In people with Crohn’s disease, osteoporosis can occur due to the intestines failing to absorb sufficient nutrients to support healthy bone growth, or due to the use of steroid medication, which may be used in the treatment of Crohn’s disease.

  • Vitamin B12 deficiency: Often signalled by fatigue and a lack of energy, vitamin B12 deficiency is likely to occur in people with Crohn’s disease due to malabsorption.

  • Pyoderma gangrenosum: This is a treatable, non-infectious skin condition,[16] characterised by painful ulcers, which typically develop purple or blue edges, and may ooze fluid. They most commonly occur on the legs.

  • Hypercoagulability: People affected by Crohn’s disease are at an increased risk of blood clots forming, which may result in deep vein thrombosis (DVT) or a pulmonary embolism if left untreated. The link between hypercoagulability and Crohn’s disease is not yet fully understood, but recent research suggests that imbalances between the levels of clotting and thinning agents in the blood caused by inflammation from Crohn’s disease, contributes to the development of the condition.[17]

  • Colorectal cancer: People whose Crohn’s disease affects their colon have a slightly increased risk of developing colorectal cancer. It is advisable to attend regular checkups and to undergo a colonoscopy to screen for colon cancer.

People with Crohn’s disease are advised to attend regular medical checkups in general, which should assist with the early identification and treatment of any associated conditions that arise.

Pregnancy and fertility

People who are affected by Crohn’s disease can normally follow their usual treatment plan during pregnancy. Most of the medications and treatment protocols, which are normally prescribed for people with Crohn’s disease, are suitable for pregnant women, with the exception of methotrexate, a type of immunosuppressant medication.[18]

Regarding the development of the fetus, Crohn’s disease has been associated with the following possible risks:[18]

  • Low birth weight
  • Preterm delivery
  • Stillbirth
  • Small gestational age

It is strongly recommended that both men and women with Crohn’s disease be in a period of remission at the point of conception. This will maximize the likelihood that the pregnancy will progress with no complications, and that the fetus will develop healthily.[19]


Approximately 1.6 million people in the U.S. are affected by either Crohn’s disease or ulcerative colitis, the other prominent form of inflammatory bowel disease (IBD).[20] The exact reasons why Crohn’s disease develops in people are unknown, but it is believed to be the result of an interaction of possible factors.

When it encounters environmental or genetic factors, or a combination of the two, the immune system can be triggered, resulting in the inflammation associated with Crohn’s disease.

  • Environmental factors: Foreign substances (antigens) which one encounters , particularly those related to smoking tobacco and to one’s diet, may irritate and cause inflammation in the intestines, resulting in the development of Crohn’s disease. Alternatively, these stimuli may correlate to an autoimmune response, whereby the body’s immune system causes areas of the gastrointestinal system to become inflamed.

Risk factors

Anyone can be affected by Crohn’s disease, but it is most likely to manifest in people between the ages of 10 and 40.

Factors which increase one’s risk of experiencing Crohn’s disease include:

  • Being of European descent, in particular of Ashkenazi Jewish origin)[21]
  • Smoking tobacco[22]
  • Being female[23]
  • Genetic factors: Having an affected family member is a significant risk factor for developing Crohn’s disease, but the exact inheritance pattern for the condition is unknown.


People often experience the symptoms of Crohn’s disease for many years before being diagnosed with the condition. In order to establish a diagnosis of Crohn’s disease, doctors will consider a person’s medical history and symptoms and will also perform a physical examination. They will often also conduct laboratory studies and further tests in order to establish the nature and severity of the condition.

Diagnostic techniques for Crohn’s disease include:[24]

  • A full survey of a person’s medical history, including when their symptoms began, their dietary habits, use of non-steroidal anti-inflammatory drugs (NSAIDs), history of smoking and whether they have a family history of Crohn’s disease or inflammatory bowel disease (IBD). Doctors will pay particular attention to noting whether they have been affected by appendicitis.

  • A physical examination which will take into account an individual’s height, weight, sex, blood pressure, body mass index (BMI), and will include a digital-rectal examination, an examination of the abdomen, as well as a survey of the eyes, joints, heartbeat, lungs, back, pulse, and the skin and muscles, where extraintestinal symptoms of Crohn’s disease may be found.

  • Laboratory studies will be performed in order to test one’s levels of electrolytes and creatinine, and a full blood count (FBC) test will be carried out to detect infection and anemia. Tests will also be performed to establish one’s levels of nitrogen, bilirubin, transferrin vitamin B12 and folic acid. Doctors will also prescribe tests to determine the individual’s erythrocyte sedimentation rate (the rate at which red blood cells coagulate), liver function tests and a urine strip to test for irregularities in the content of their urine.

  • Imaging studies such as MRI and CT scans will be used to screen extraintestinal symptoms such as fistulas, abscesses or sclerosing cholangitis (liver disease). People who are suspected of having Crohn’s disease will often undergo an ileocolonoscopy, in which a tube-like device containing a camera is passed through the colon in order to examine the ileum, and/or an esophagogastroduodenoscopy, in which the tube-like device is swallowed in order to examine problems relating to the upper gastrointestinal tract.
    If it is not possible to scan the terminal ileum using conventional imaging studies, a wireless capsule endoscopy may be prescribed, which involves swallowing a small device containing a camera. This is often used to investigate unexplained bleeding in the gastrointestinal area.[25]

  • Biopsy samples from at least five segments of the gastrointestinal tract will be taken during the esophagogastroduodenoscopy in order to investigate the extent of the inflammation, and the inflammatory cell infiltrate, lymphocytes and plasma cells.

  • Stool samples will be taken to test for the presence of the Clostridium difficile bacteria, which causes diarrhea and gastrointestinal conditions.

  • Microbial studies via stool samples will be performed to identify the microorganisms, including pathogens and members of the indigenous microbiota, which may be present in an individual’s gastrointestinal system and which may initiate or propagate the inflammatory process characteristic of Crohn’s disease.[26]

The testing process to determine a definitive diagnosis of Crohn’s disease is thorough. This is due to the fact that the condition is one of many, which are associated with pain and cramping in the abdomen.

Conditions which are often confused with Crohn’s disease, and which will be ruled out during the course of the diagnostic process include:

  • Stomach ulcers
  • Gastritis (stomach irritation)
  • Irritable bowel syndrome (IBS), which has similar symptoms to Crohn’s disease, but is a much less serious - condition, which does not result in damage to the intestine
  • Gastrointestinal reflux disease (GERD)
  • Appendicitis
  • Ulcerative colitis, the other main form of inflammatory bowel disease

The final step in the diagnosis of Crohn’s disease involves collecting information to devise a treatment plan for the affected individual. This assessment will be performed by a doctor specialising in diseases of the gastrointestinal tract, called a gastroenterologist.

This initial assessment will establish:[27]

  • The extent of the disease
  • Complications such as fistulae and stricturing
  • Nutritional status and deficiencies
  • Bone density and the corresponding risk of conditions such as osteoporosis


There is currently no cure for Crohn’s disease, but there are many treatment options available to alleviate the symptoms.

*Treatment for Crohn’s disease focuses on:

  • Treating the symptoms
  • Minimising flare ups
  • Maintaining periods of remission

With effective treatment, many people with Crohn’s disease will experience significant periods, possibly several years, without symptoms. For people with more severe forms of the condition, and for whom medications do not provide significant relief from the symptoms, surgery may be required.

Steroid medication

Initial treatment of Crohn’s disease will usually involve the prescription of steroid medications (corticosteroids), which are used to reduce inflammation. These may take the form of tablets or injections, depending on what is determined to be suitable for the affected individual.[28]

However, long-term usage of corticosteroids are associated with problematic side effects, which may include:

  • Swelling of the face
  • Unwanted weight gain
  • Increased susceptibility to infections
  • Bone density loss and resultant osteoporosis

When a person embarks on a course of corticosteroid medication, an aim of this treatment will usually be to reduce the dose over time, so as to minimise one’s exposure to harmful side effects.

As an alternative to corticosteroids, some people may be prescribed a milder steroid or a type of medication called a 5-aminosalicylate. However, these tend to be less effective at alleviating gastrointestinal inflammation.

Polymeric diet

For individuals, whose growth and development may have been affected by Crohn’s disease, a polymeric (liquid) diet administered through a nasogastric tube may be recommended as an initial treatment. Many studies have been undertaken, comparing the polymeric diet to steroid medication, and it is considered an equally effective first-line treatment for Crohn’s disease.[29]

A polymeric diet will be prescribed in order to allow the digestive system to recover from being inflamed and to support the uptake of nutrients, a process which is often compromised by the inflammation that is characteristic of Crohn's disease.[29]

A person who has been prescribed a polymeric diet will progress to slowly reintroducing solid foods into their diet in a controlled setting, in order to safeguard the period of remission facilitated by undertaking the liquid diet.[30]


If a person, who is being treated with corticosteroids or the polymeric diet, experiences a flare up of their symptoms twice or more during one year, or finds that they return when their steroid dose is reduced, medicines which suppress the immune system (immunosuppressants) may be prescribed in combination with the initial course of treatment.

The immunosuppressant medications which are most commonly prescribed for the treatment of Crohn’s disease are azathioprine and mercaptopurine. They work by damping down the over-activity of the cells within the immune system.[31] An alternative medication is methotrexate, a form of immunosuppressant which is not recommended for use during pregnancy.

It is vital that a blood test is performed before immunosuppressant medication is prescribed. A high score on this test relating to factors such as an elevated white blood cell count and increased lymph production, may indicate immunosuppressant toxicity, which means that these medications are not suitable for the affected individual.[32]

People who are using immunosuppressant medication in the treatment of Crohn’s disease will undergo regular blood tests in order to ensure that the medication continues to agree with them, so that their use can be discontinued if needed, averting the presence of unwanted side effects.

Possible side effects of immunosuppressant medication include:

  • Nausea and vomiting
  • Susceptibility to infection
  • Inflammation of the pancreas (pancreatitis)
  • Liver problems
  • Anemia, characterised by feeling tired, breathless and weak

Biologic therapies

Biologic therapies are a type of immunosuppressant medications which use substances, such as antibodies and enzymes, to inhibit the effects of Crohn’s disease.

The development of biologic therapies therefore presents a breakthrough alternative treatment option for those who are unwilling or unable to use steroid medication. Historically, people with Crohn’s disease and other types of IBD faced a lack of effective treatment options. Corticosteroid therapy does not alleviate the symptoms of Crohn’s disease in all cases and for those whose symptoms do not respond to it, prolonged systemic corticosteroid therapy and surgery were previously the only options.[33]

If a person responds well to biologic therapy, its benefits may include:

  • Removal of the need to use steroid medication, thereby avoiding its side effects
  • Prolonged periods in which the disease is in remission
  • Potential delay or negation of the need for surgery to redress intestinal damage caused by Crohn’s disease

Why is biologic therapy not always offered as a first-line treatment?

Medical opinion is divided as to whether biologic therapies should be a first-line treatment option, and many doctors prefer to investigate whether a case of Crohn’s disease can be treated with corticosteroids, a liquid diet or traditional immunosuppressants initially, before considering biologic therapy.

The principal reason that some doctors prefer to prescribe traditional treatment methods first is that less is understood about the mechanism of action of biologic medications, and how different people will respond to them. Allergic reactions to the medications used in biologic therapies may occur –immediately or months after stopping treatment – and these can be life-threatening.

Methods of administration

The two medications used in biologic therapy for Crohn’s disease are Infliximab and Adalimumab.

These medications are considered to be broadly comparable in terms of their effectiveness in bringing about prolonged periods of remission and preventing the development of complications, such as intestinal obstructions, which require surgery.[34] Both children and adults can be prescribed Infliximab but Adalimumab is only suitable for adults.

Both medications are usually prescribed on a twelve month course, after which the need to continue will be reviewed, based on the individual’s response and the stability of the periods of remission following dosing.

Infliximab is administered as an infusion via a drip into a vein and requires one to visit a hospital to receive the medication as an outpatient procedure.

Adalimumab can be administered as an injection, and one can learn to do this independently or with the help of another person, meaning that hospital visits are not necessary in order to redose. Doctors will advise on the type of medication that is appropriate in each individual case of Crohn’s disease.


The type of surgical procedure which will be prescribed in this case is called a resection. Doctors will consider performing a resection to remove the inflamed sections of the intestinal tract in cases where the symptoms of Crohn’s disease have not been alleviated by other treatments.

A resection is a major procedure and usually performed under general anaesthetic. When the inflamed sections of the intestine have been removed, the healthy sections will be stitched together.

Ileostomy (temporary or permanent)

An ileostomy is a procedure which involves diverting one’s digestive waste away from the colon in order to give the area, which has undergone a resection, a chance to heal.[35] This can be temporary or permanent.

The type of ileostomy prescribed as an adjunct to a resection is usually a loop ileostomy, a temporary version of ileostomy, performed under general anaesthetic, which will be reversed after the body has had a chance to recover from undergoing resection surgery.[36]

In a loop ileostomy, an opening in the lower abdominal area, called a stoma, is surgically created. An ileostomy bag is then attached to the small intestine through the stoma. The bag hangs outside the body and collects the waste products that would otherwise have passed into one’s large intestine and out of one’s rectum.[36] Normal function of the digestive system will be restored when the ileostomy is reversed.

A loop ileostomy is not always necessary as an accompaniment to a resection. One’s physician will advise on whether the procedure is needed.


One’s lifestyle, exercise routine and diet plan will generally need to be tailored to one’s individual needs as determined by one’s condition, and may need to be adjusted according to one’s symptoms.

Managing Crohn’s disease can involve:

  • Maintaining periods of remission
  • Making lifestyle adjustments to accommodate medical appointments
  • Management of pain and digestive discomfort
  • Co-ordinating an appropriate lifestyle whilst undergoing treatment
  • Surgery aftercare

Changing one’s diet after surgery may be necessary: A potential outcome of surgery for Crohn’s disease is short bowel syndrome, a condition in which malabsorption occurs due to lack of a functional small intestine. Short bowel syndrome, when present, develops in the recovery period after an intestinal resection. The likelihood of a person developing problems associated with malabsorption increases, the more intestinal tissue is removed.

In order to ensure that the affected person receives as much nutritional benefit from their food as possible, dietary changes may be required. Doctors will advise on the most appropriate food plan for each person, in order to reduce the chances of vitamin and mineral deficiencies after surgery.


Crohn’s disease is a chronic condition, which means that one must make certain adjustments to one’s lifestyle, including accepting that treatment and management of the condition will always be a part of one’s life. One may find it helpful to educate one’s loved ones and co-workers about the condition, so that they are understanding when one has to miss commitments or take time off work due to a flare-up.

People with Crohn’s disease will undergo periods when they need to attend frequent medical appointments for tests and/or treatment, and even when one is in a period of remission, one may need to attend checkups and periodic screenings for conditions, such as bowel cancer and osteoporosis, for which Crohn’s disease is a risk factor. It is therefore important to establish a good working relationship with one’s gastroenterologist.

Travelling with Crohn’s disease will require advance planning in order to ensure that one has, or is able to access, the pharmaceuticals that one is using to manage the condition. It is recommended that one identifies in advance how to seek medical attention in one’s destination location in the event of a flare-up.

Knowing the location of nearby restrooms can be helpful to people with Crohn’s disease as one is prone to diarrhea and may need to access a restroom rapidly. Checking the location of public restrooms in advance when visiting a new area is recommended, in order to ensure that toilets are accessible when needed.


It is important for everybody to engage in a certain amount of physical activity in order to maintain a healthy body. This includes people who are affected by Crohn’s disease. However, inflammation, fatigue and urgency are all factors which mean that an individual with Crohn’s disease will need to identify the appropriate fitness plan for them. Physical activity which is too intense may exacerbate the inflammation in people affected by Crohn’s disease.

There has not been significant research into the ideal types and intensities of physical activity for different levels of severity of Crohn’s disease. However, a recent review of current research suggests that a personalized exercise plan would be ideal.[37]

This should be devised taking into account factors such as:[37]

  • Age
  • Fitness level
  • Exercise goals
  • Preferences
  • Severity of one’s Crohn’s disease and associated needs, such as proximity to restrooms

The types of activity which have been found convenient and helpful for people with Crohn’s disease, include:[37]

  • Aerobic activity, especially walking
  • Muscular resistance training, which can be carried out at home, if necessary


There is currently no dietary template to follow in order to minimize the symptoms of Crohn’s disease. Individuals react differently to different foodstuffs, and everybody will find it helpful to avoid particular foods, which appear to aggravate their symptoms.

However, there are some general principles which are widely acknowledged to be helpful in preventing flare-ups of Crohn’s disease symptoms, including:

  • Eating smaller meals which are easier to digest
  • Drinking plenty of water
  • Keeping a food diary to ensure a balanced diet and to track adverse reactions to particular foods
  • Monitoring one’s fiber intake to discern whether high-fiber products trigger one’s symptoms
  • Choosing low-fat products
  • Avoiding foods which produce excessive bloating and gas

Other names for Crohn’s disease

  • Crohn’s syndrome
  • Regional enteritis

  1. Does inflammatory bowel disease develop in infants?”. Inflammatory Bowel Disease. October 2008. Accessed: 28 November 2017.

  2. Crohn’s disease: symptoms.” NHS Choices. 17 April 2015. Accessed: 28 November 2017.

  3. Abdominal pain and cramps.” 2017. Accessed: 28 November 2017.

  4. Diarrhoea and constipation.” Crohn’s & Colitis, UK. April 2016. Accessed: 28 November 2017.

  5. Determinants of fatigue in Crohn's disease patients.” European Journal of Gastroenterology & Hepatology. 25 February 2013. Accessed: 28 November 2017.

  6. Crohn’s disease and fatigue.” IBD News Today. 16 October 2017. Accessed: 28 November 2017.

  7. Vitamin D and Inflammatory Bowel Disease.” Gastroenterology & Hepatology. August 2016. Accessed: 28 November 2017.

  8. Malnutrition and impaired muscle strength in patients with Crohn's disease and ulcerative colitis in remission.” Nutrition. July 2008. Accessed: 28 November 2017.

  9. Rectal bleeding.” 2017. Accessed: 28 November 2017.

  10. Diseases associated with mucus in the bowel.” Livestrong. 14 August 2017. Accessed: 28 November 2017.

  11. Small bowel obstruction secondary to Crohn disease: CT findings.” Abdominal Imaging. MAy 2004. Accessed: 28 November 2017.

  12. Anal fissures in Crohn's disease and ulcerative colitis.” IBD Relief. 2017. Accessed: 28 November 2017.

  13. Abscess and fistula expanded information.” American Society of Colon and Rectal Surgeons. Accessed: 28 November 2017.

  14. Fistulas and inflammatory bowel disease (IBD).” IBD Relief. 2017. Accessed: 28 November 2017.

  15. Anemia in Crohn’s disease.” Digestive Diseases and Sciences. September 1994. Accessed: 28 November 2017.

  16. Pyoderma gangrenosum.” British Skin Foundation. Accessed: 28 November 2017.

  17. “[Blood clotting disorders (hypercoagulable states)](].” Cleveland Clinic. 2017. Accessed: 28 November 2017.

  18. Sexuality, fertility, and pregnancy in Crohn’s disease.” Gastroenterology Clinics of North America. 19 July 2017. Accessed: 28 November 2017.

  19. Crohn’s disease in women.” International Journal of Women’s Health. 18 October 2013. Accessed: 28 November 2017.

  20. Living with Crohn’s disease.” Crohn’s & Colitis Foundation of America. 2017. Accessed: 28 November 2017.

  21. A genome-wide scan of Ashkenazi Jewish Crohn's disease suggests novel susceptibility loci.” PLOS Genetics. 08 March 2012. Accessed: 28 November 2017.

  22. Tobacco and IBD: relevance in the understanding of disease mechanisms and clinical practice.” Best Practice & Research Clinical Gastroenterology. June 2004. Accessed: 28 November 2017.

  23. Risk factors.” 2017. Accessed: 28 November 2017.

  24. Crohn’s disease.” The Lancet. 20 August 2012. Accessed: 28 November 2017.

  25. Wireless capsule endoscopy for investigation of the small bowel.” National Institute for Healthcare and Excellence (NICE). December 2004. Accessed: 28 November 2017.

  26. The role of microbes in Crohn’s disease.” Clinical Infectious Diseases. 15 January 2007. Accessed: 28 November 2017.

  27. Crohn's disease for the general physician: management.” British Journal of Hospital Medicine. 06 February 2017. Accessed: 28 November 2017.

  28. Steroids (corticosteroids).” Crohn’s & Colitis UK. June 2016. Accessed: 28 November 2017.

  29. Polymeric enteral diets as primary treatment of active Crohn's disease: a prospective steroid controlled trial.” British Medical Journal. 01 June 1993. Accessed: 28 November 2017.

  30. Treating Crohn’s Disease with Diet.” Nutricia: Advanced Medical Nutrition. May 2012. Accessed: 28 November 2017.

  31. Azathioprine and Mercaptopurine.” Crohn’s & Colitis UK. 2017. Accessed: 28 November 2017.

  32. Immunosuppressant Medications Blood Test.” DoveMed. 02 June 2016. Accessed: 28 November 2017.

  33. Biologic therapies for Crohn's disease.” January 2010. Gastroenterology & Hepatology. January 2010. Accessed: 28 November 2017.

  34. Comparative effectiveness of Infliximab and Adalimumab in Crohn's disease and ulcerative colitis.” April 2016. Accessed: 28 November 2017.

  35. Surgery for Crohn’s disease and ulcerative colitis.” Crohn’s & Colitis Foundation of America. 2017. Accessed: 28 November 2017.

  36. Ileostomy.” NHS Choices. 29 March 2016. Accessed: 28 November 2017.

  37. Prescription of physical exercise in Crohn's disease.” Journal of Crohn’s and Colitis. December 2009. Accessed: 28 November 2017.