What is Crohn’s disease?

What is Crohn’s disease?

Crohn’s disease (CD) is a chronic (long-term) inflammatory condition affecting the lining of the digestive system.1

Although any part of the gastrointestinal tract (GI) can be affected, from the mouth to the anus, Crohn’s disease most commonly occurs in the colon (the large intestine) or the last part of the small intestine (the ileum).1 The inflammation can penetrate the thick lining of the bowel wall and may occur in patches, affecting some areas but not others.2

Symptoms of Crohn’s disease

The way Crohn's disease affects different people is highly individual, and changes over time. Long periods of remission, where you have few symptoms or no symptoms at all, are punctuated by 'flare-ups' or relapses, when symptoms become active.1

The most prominent and common symptoms that most people experience at one time or another are:2,3

Diarrhoea or urgently needing the toilet

Your poo may be looser than normal, more frequent than is usual for you, and blood or mucus may be present

Stomach pains

Cramping pains in the lower abdomen

Tiredness (fatigue)

Extreme tiredness due to sleep disturbance, anaemia or flare-ups

Weight loss

You might lose your appetite when you feel unwell and gut inflammation can prevent the absorption of nutrients


Raised temperature, feeling unwell or feverish

Blood in stool

Sometimes poo may contain mucus, blood or pus

Types of Crohn’s disease

Crohn’s disease can affect any part of the digestive system and this can affect the symptoms you experience and the possible treatments that are offered to you.2,3

You might have a type that affects just one area, or a combination of locations may be affected.

Infographic showing the ileum, the last portion of the small intestine, highlighted from the rest of the gastrointestinal tract.
Ileal (also called terminal ileal)

Affects the last part of the small intestine (the ileum), where it meets the colon. If the beginning of the large bowel is also affected, it is known as ileocaecal Crohn’s

Infographic showing the ileum and jejunum, the central portion of the small intestine, highlighted from the rest of the gastrointestinal tract.
Small bowel (also called ileitis or jejunoileitis)

Affects the ileum or jejunum, parts of the small bowel

Infographic showing the colon, the large bowel, highlighted from the rest of the gastrointestinal tract.
Crohn’s colitis

Only the colon is affected – the large bowel

In severe Crohn’s disease, patients can develop a narrowing in the bowel (a stricture) which may require surgery.2

In some rare cases, serious complications can occur, such as a perforation or rupture of the bowel (around 2 in 100 people with Crohn’s), which allows the contents of the bowel to leak through the bowel wall. A leak that goes on to form an abscess is a medical emergency, and you should see a doctor as soon as possible.3

Find out more about Getting diagnosed

Outside the gut

Complications of CD that affect areas outside the digestive tract are sometimes called ‘extraintestinal’ symptoms, such as:1,2

  • Bones can become thinner and weaker
  • Skin may become inflamed
  • Eyes may become inflamed
  • Liver, lungs or other organs: complications can include kidney stones, gall stones, blood clots, hair loss, and anaemia

Always mention any new or changing symptoms you have to your doctor – even if they are not related to CD they should be addressed if they affect your quality of life.

A patient consulting with an IBD nurse and discussing her medical records

Management, treatment and monitoring

If you have been diagnosed with Crohn’s disease or ulcerative colitis you might want to find out about:

Two people talking about their IBD condition
A woman suffering from stomach pain, a symptom of IBD
A patient interacting with her IBD healthcare team in the NHS
An IBD nurse discussing treatment options with patients

Patient advocacy groups

You can find out more about inflammatory bowel disease from these independent organisations.

Crohn’s and Colitis UK

The Crohn’s & Colitis UK website provides information on a range of issues relating to both Crohn’s disease and ulcerative colitis, with helpful guides about the conditions, how they are treated and how to live with them. The charity provides a range of other support, including helpline services, local volunteer networks and an active membership community of over 40,000 people

IBDrelief logo.

IBDrelief provides information about various aspects of all types of IBD. It provides help with understanding the disease, its treatments and living with IBD, and shares first-hand accounts from people with IBD

*IBDrelief patient survey data from 167 respondents with IBD in the UK. 58% of respondents who did not discuss emotional wellbeing with their consultant gave a lack of time as the reason.5


CD = Crohn’s disease; IBD = inflammatory bowel disease; UC = ulcerative colitis.

  1. NHS Inform. Crohn’s disease. www.nhsinform.scot/search?q=crohns&locpt=55.378051%2C-3.435973&ds=&tab=inform. Accessed October 2023.
  2. Roda G, et al. Crohn’s disease. Nat Rev Dis Primers. 2020;6(1):1-9.
  3. Peyrin-Biroulet L, et al. Long-term complications, extraintestinal manifestations, and mortality in adult Crohn's disease in population-based cohorts. Inflamm Bowel Dis. 2011;17(1):471-8.
  4. IBDrelief. Impact of IBD on physical and emotional health: Findings from an IBDrelief survey. Available at https://www.ibdrelief.com/impact-of-ibd-on-physical-and-emotional-health. Accessed October 2023.