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Understanding Inflammatory Bowel Disease (IBD)

Understanding inflammatory bowel disease (IBD): how Crohn’s disease and ulcerative colitis differ, their symptoms, diagnosis and treatment

Feeling very unwell? See when to get urgent help: the signs that mean you should contact a doctor the same day, or call emergency services. If you’re struggling to cope, see crisis lines, open day and night.

Inflammatory bowel disease (IBD) is an umbrella term for conditions that cause long-term inflammation of the gut (the gastrointestinal, or digestive, tract).

Crohn’s disease and ulcerative colitis are the two main types of IBD.[1] When someone has features of both and doctors can’t yet tell which one it is, it is called IBD unclassified (IBD-U). You may also see the older name, indeterminate colitis.

Microscopic colitis is a related condition: the bowel looks normal during a colonoscopy (a camera test of the large bowel), and the inflammation only shows up under a microscope. It is usually treated as a separate condition rather than a type of IBD.

Some conditions (such as Behçet’s disease) can cause gut symptoms that look very like IBD, but doctors treat them as separate conditions.

These conditions are characterised by periods of active disease (flares) and periods of remission (when symptoms are reduced or absent).

Looking for something specific? Find help by topic, from symptoms to support.

The health information on this page comes from the patient charities and health services listed under References. It has not been reviewed by a clinician: read how the health information is prepared.

What is Crohn’s Disease?

Crohn’s disease is a type of IBD that can affect any part of the gut, from the mouth to the anus, but most commonly affects the end of the small intestine (ileum) and the beginning of the colon. In Crohn’s disease:

  • Inflammation may extend through all layers of the bowel wall.[2]
  • Affected areas may be patchy, with healthy sections in between (known as “skip lesions”).
  • Common symptoms include abdominal pain, diarrhoea, fatigue, weight loss and malnutrition.
  • Complications can include strictures (narrowing of the intestine), fistulas (abnormal connections between organs) and abscesses.[3]

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What is Ulcerative Colitis?

Ulcerative colitis is a type of IBD that affects only the colon (large intestine) and rectum. In ulcerative colitis:

  • Inflammation is typically limited to the innermost lining of the colon.[4]
  • The inflammation is continuous, starting from the rectum and potentially extending throughout the colon.
  • Common symptoms include bloody diarrhoea, abdominal cramping, a sudden and urgent need to go to the toilet (bowel urgency) and fatigue.
  • Complications can include severe bleeding, toxic megacolon (a dangerously swollen colon) and an increased risk of colorectal cancer.[5]

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Both Crohn’s disease and ulcerative colitis:

  • Are chronic inflammatory conditions of the digestive tract
  • Have similar symptoms and can have a big effect on daily life
  • Are thought to happen when the immune system overreacts to something in the environment, in people whose genes make them more likely to get IBD[6]
  • Have no known cure, but treatments can help manage symptoms and achieve remission
  • Can start at any age, but are most often diagnosed in young adults: Crohn’s disease most commonly before the age of 30, and ulcerative colitis between 20 and 40[7][10]
More detail: what causes IBDHide detail: what causes IBD

In medical terms, IBD is thought to come from an abnormal immune response to triggers in the environment, in people whose genes make them susceptible.[6] Researchers have found more than 200 genetic variations that affect the risk of developing Crohn’s disease, and many are in genes that control the immune system. Changes in these genes may alter how the immune system responds to bacteria in the gut, and together with other genetic and environmental factors they can lead to ongoing inflammation. More research is needed to know for certain what causes it.[7]

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How Do They Differ?

Despite their similarities, there are important differences between Crohn’s disease and ulcerative colitis:

Crohn’s disease and ulcerative colitis compared
FeatureCrohn’s DiseaseUlcerative Colitis
LocationCan affect any part of the GI tractLimited to the colon and rectum
PatternPatchy inflammation with skip lesionsContinuous inflammation
DepthCan affect all layers of the bowel wallTypically affects only the innermost lining
ComplicationsStrictures, fistulas, abscessesSevere bleeding, toxic megacolon
SurgeryOffered when medicines aren’t controlling symptoms, for complications such as a narrowed section of gut or an abscess, or by choice. Common operations widen a narrowed section, or remove the damaged section and join the healthy ends back together. Some people need a stoma, where waste leaves through an opening on the tummy into a bag; it can be temporary or permanent. Surgery cannot cure Crohn’s disease, which can come back in another part of the gut, but most people find life is better afterwards. Around 1 in 5 people need major surgery within 5 years of diagnosis.[21]Offered when medicines aren’t controlling symptoms, for severe complications, or by choice. Removing the whole large bowel (the colon and rectum) means colitis can’t come back in the gut, though some symptoms outside the gut can continue. Afterwards, waste leaves through a stoma into a bag, or is stored in an internal pouch made from the small bowel (a J-pouch). Around 7 in 100 people need major surgery within 5 years of diagnosis.[22]
More detail: types of Crohn’s disease and ulcerative colitisHide detail: types of Crohn’s disease and ulcerative colitis

Doctors describe both conditions by where they are in the gut. Crohn’s disease is most common in the small bowel and the colon. Crohn’s in the small bowel is called ileitis (or jejunoileitis, depending on the part affected), and Crohn’s in the area around the anus is called perianal Crohn’s. Perianal symptoms can come on their own or with inflammation elsewhere in the gut.[7]

Ulcerative colitis is described by how far up the large bowel it reaches:[10]

  • Proctitis: only the rectum, the lowest part of the large bowel. About 1 in 10 people with proctitis later develop colitis that affects most of the colon.
  • Proctosigmoiditis: the rectum and the part of the colon next to it (the sigmoid colon).
  • Left-sided or distal colitis: the rectum and the left side of the colon (the descending colon).
  • Extensive colitis: most of the colon, but not all of it.
  • Total colitis, also called pancolitis: the whole colon.

Surgery

Surgery is offered when medicines aren’t controlling symptoms, or for complications, and some people choose it rather than trying more medicines. For Crohn’s disease it removes the damaged part of the gut, which can ease symptoms but doesn’t cure the condition. For ulcerative colitis, removing the whole large bowel means colitis can’t come back in the gut. The “Surgery” row of the table above has more detail on each.[21][22]

Some operations leave you with a stoma (called an ostomy in North America): an opening on your tummy, with a bag to collect waste.[19][20] A stoma can be temporary or permanent, in either condition, and some people with ulcerative colitis have an internal pouch made from the small bowel (a J-pouch) instead.[21][22] Stoma and ostomy charities can put you in touch with people who have been through it: see stoma and pouch support for Australia, Canada, New Zealand, the United Kingdom and the United States.

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Could It Be IBD?

See a GP (your family doctor) if you think you could have Crohn’s disease or ulcerative colitis, for example because you have some of the symptoms described above. Ask for an urgent appointment if your poo is black or dark red or you have bloody diarrhoea, and see When to Get Urgent Help for the signs that need emergency care. If your GP thinks you could have IBD, they may arrange blood tests and a test on a sample of your poo, and refer you to a specialist in hospital for more tests to confirm it.[19][20]

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When to Get Urgent Help

Contact your doctor or IBD team (the hospital specialists and nurses who look after your IBD) the same day if you have symptoms of Crohn’s disease or ulcerative colitis and:[19][20]

  • your poo is black or dark red, or you have very bad or bloody diarrhoea
  • you have a high temperature, or feel hot, cold or shivery
  • you have a fast heartbeat
  • you can’t pass wind or poo
  • your symptoms are getting worse quickly, or you’re worried about them

If you can’t reach them, for example at night or at the weekend, call the free health advice line where you live:

  • Australia: healthdirect on 1800 022 222, anywhere in Australia. In Queensland only, you can also call 13 HEALTH on 13 43 25 84.
  • Canada: 811 in most provinces and territories. In Manitoba, call Health Links – Info Santé on 1-888-315-9257 (204-788-8200 in Winnipeg).
  • New Zealand: Healthline on 0800 611 116.
  • United Kingdom: 111 in England, Scotland and Wales (NHS 111, or NHS 24 in Scotland). In Northern Ireland, contact your GP out of hours service instead.
  • United States: there is no national advice line; call your doctor’s after-hours number. If you can’t reach them, after-hours care options include a nurse advice line through your health insurance or an urgent care clinic.

Call emergency services or go to an emergency department if:[20]

  • you have severe tummy pain
  • you’re bleeding from your bottom and it won’t stop
  • there’s a lot of blood or there are large clots when you poo
  • you’re vomiting blood or poo, or your vomit looks like coffee grounds or soil

Emergency numbers: Australia 000; Canada and the United States 911 (Nunavut and some remote communities have no 911 service: use your community’s local emergency number); New Zealand 111; United Kingdom 999. Anywhere else, call your local emergency number. Don’t drive yourself: ask someone to take you, or call an ambulance.

If you’re having thoughts of harming yourself, or feel you can’t cope, see the crisis lines you can call or text at any time.

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Diagnosis

Diagnosing IBD usually needs an endoscopy, where a doctor looks inside your gut using a thin, flexible tube with a camera on the end. This also helps tell Crohn’s disease and ulcerative colitis apart. Reaching a diagnosis may involve a combination of:

  • Medical history and physical examination
  • Blood tests to check for anaemia, inflammation markers and antibodies
  • Stool tests to rule out infections and check for inflammation
  • Imaging studies such as computed tomography (CT) scans, magnetic resonance imaging (MRI) and intestinal ultrasound (IUS)[8]
  • Endoscopy: a colonoscopy (of the large bowel), a gastroscopy, also called an upper endoscopy (of the food pipe, stomach and first part of the small bowel), or both
More detail: the hospital testsHide detail: the hospital tests

There is no single test for Crohn’s disease, and a diagnosis often takes time because the symptoms vary and can be like those of other conditions. Hospital tests may include:[19]

  • Endoscopy: a thin tube with a small camera is passed through your bottom or your throat to look inside your gut. A colonoscopy looks at the large bowel; a gastroscopy (upper endoscopy) looks at the food pipe, stomach and the start of the small bowel.
  • A biopsy: a small sample of tissue taken from your gut during the endoscopy.
  • Scans, such as an MRI, CT or ultrasound scan.

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Treatment

There is no single treatment for IBD. Your IBD team will work with you to find the combination that suits you, which may include:

  • Aminosalicylates (5-ASAs), such as mesalazine, which calm inflammation in the gut lining
  • Steroids, such as prednisolone or budesonide, for short periods to bring a flare under control
  • Immunosuppressants, such as azathioprine, mercaptopurine and methotrexate, which damp down the immune system
  • Biologic therapies: medicines made from living cells that block specific parts of the immune system; the main types (TNF inhibitors, integrin inhibitors and interleukin inhibitors) are explained below
  • Small molecule drugs: medicines taken by mouth, such as JAK inhibitors, and for ulcerative colitis, S1P receptor modulators
  • Nutritional therapy, such as a liquid-only formula diet for several weeks (exclusive enteral nutrition), which is often used for children with Crohn’s disease
  • Antibiotics
  • Surgery: see what surgery involves[9][24]
More detail: how the medicines workHide detail: how the medicines work

Each type of medicine calms inflammation in a different way:[24]

  • Aminosalicylates (5-ASAs), such as mesalazine, work directly on the bowel lining. They are not immunosuppressants, so they don’t affect how the immune system works in the rest of your body.
  • Steroids, such as prednisolone and budesonide, lower the activity of the immune system, which brings inflammation down. They are usually given as a short course to control a flare.
  • Azathioprine and mercaptopurine (thiopurines) lower the activity of the immune system, which reduces inflammation in the gut. They can be taken on their own, or alongside a biologic such as adalimumab or infliximab to help the biologic work properly. They can take 3 months or more to start working.
  • Methotrexate also changes the way the immune system works. It is used mainly for Crohn’s disease. It is taken once a week, usually with folic acid to reduce side effects.
  • TNF inhibitors (anti-TNFs), such as infliximab and adalimumab, block a protein called TNF-alpha. Your body makes TNF-alpha to fight infections, but too much of it can damage the cells that line the gut.
  • Vedolizumab, an integrin inhibitor, sticks to a protein called integrin on the surface of white blood cells that enter the gut. Blocking integrin stops those cells getting into the gut, so it is called gut-selective.
  • Interleukin inhibitors block interleukins, proteins that help control the immune system. Ustekinumab blocks interleukins 12 and 23 (IL-12 and IL-23), and risankizumab blocks IL-23.
  • JAK inhibitors, such as tofacitinib, block proteins called Janus kinases (JAKs) that help switch on the immune response. Because they block specific proteins, they are called targeted medicines.
  • S1P receptor modulators, such as ozanimod, stop a type of white blood cell (a lymphocyte) travelling around the body and into the gut. They are used for ulcerative colitis.

Some people take two medicines together, for example adalimumab with azathioprine or methotrexate. This is called combination therapy.[24]

Medicines can have side effects. Prescription medicines usually come with a leaflet that explains how to take them and lists their known side effects (in Australia, the Consumer Medicine Information, or CMI). It is often inside the medicine packaging, or you can ask your pharmacist or doctor to print it for you. If you are unsure about a medicine, talk to your doctor or pharmacist.[26]

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Living with IBD

Crohn’s disease and ulcerative colitis are lifelong conditions, and there is no cure yet. Most people have times when their symptoms are under control (remission) between flares.[7][10] Your IBD team, and the organisations listed for your country, can help you live well with it.

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Just Diagnosed

Hearing that you have Crohn’s disease or ulcerative colitis can be a lot to take in, and it’s natural to have lots of questions. Take it at your own pace. Some practical first steps:[23]

  • Find out whether your hospital or clinic has IBD nurses (specialist nurses who look after people with IBD) and how to contact them. They can help with questions between appointments.
  • Tell your GP about your diagnosis and where you’ll be receiving your IBD care.
  • There are many different medicines for Crohn’s and colitis, and it may take some time to find the one that works for you.
  • Look after yourself. Tiredness (fatigue) is common, and a new diagnosis can affect how you feel, so it’s OK to take time for yourself. The sections below cover food, mental health and other everyday questions.
  • Get in touch with the national IBD charity where you live. Many run a helpline, and they can put you in touch with other people who understand. Find the organisations for your country.

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Looking After Yourself

Living with IBD is about more than medicines. These everyday topics come up for most people at some point.

Mental Health

Feeling anxious or low is common with IBD. A review that pooled 77 studies found symptoms of anxiety in about 1 in 3 people with IBD (32%) and symptoms of depression in about 1 in 4 (25%).[12] If you’re struggling, tell your GP or IBD team, just as you would about any other symptom. Mind Over Gut, run by a clinical psychologist and researcher at Swinburne University in Melbourne, has free information about IBD and a free online programme to help people with gut conditions cope with stress, worry and low mood; taking part in the programme also helps its research.[27] It isn’t a crisis service: for urgent support, use the lines below.

If you feel you can’t cope, or you’re having thoughts of harming yourself, you can talk to someone now. These lines are open day and night, and most calls are free:

If your life is in danger, call your emergency number now (see When to Get Urgent Help).

Smoking

Smoking increases the risk of developing Crohn’s disease and makes Crohn’s disease worse. If you have Crohn’s, it’s never too late to quit: once you stop, your chances of a flare or of needing surgery become the same as someone who doesn’t smoke. People who smoke are less likely to develop ulcerative colitis, but that doesn’t make smoking safe or helpful, and everyone with Crohn’s disease, ulcerative colitis or microscopic colitis is advised not to smoke.[13]

Food and Diet

There is no evidence that any particular diet can cure Crohn’s disease or ulcerative colitis, and what works for one person might not work for another. Try to eat a healthy, balanced diet. Experts don’t recommend cutting out whole foods or food groups, because you could miss out on nutrients your body needs, so speak to your GP, IBD team or a dietitian before making any big changes.[14]

Vaccinations

Many IBD medicines suppress your immune system (they are immunosuppressants): steroids, azathioprine, mercaptopurine, methotrexate, biologics, JAK inhibitors and S1P receptor modulators. Aminosalicylates (5-ASAs) are not. If you take an immunosuppressant, you should not have any “live” vaccines, such as the MMR, chickenpox, yellow fever or nasal spray flu vaccines. Non-live vaccines, including the flu injection, COVID-19 vaccines, the pneumococcal vaccine and the non-live shingles vaccine, are safe to have.[15] Whether you count as immunosuppressed can depend on the medicine, the dose, how long you have taken it and what you take with it, so check with your IBD team before having any live vaccine.[25] Some medicines, such as infliximab, may make the flu and COVID-19 vaccines work less well.[16] Ask your IBD team which vaccines are right for you.

Pregnancy

Most women with Crohn’s disease or ulcerative colitis can expect straightforward pregnancies and healthy babies. Complications are more likely if the condition is active during pregnancy, so many women are advised to keep taking their medicines to keep it under control. Many IBD medicines are considered safe to take during pregnancy, but always talk to your IBD team before you stop, start or change a medicine. A few medicines are not suitable during pregnancy, including methotrexate, mycophenolate, JAK inhibitors (tofacitinib, filgotinib and upadacitinib) and S1P receptor modulators (ozanimod and etrasimod). If you become pregnant while taking one of these, contact your IBD team straight away for advice. Don’t stop or change any medicine on your own unless your doctor or IBD team tells you to. If you can’t reach your IBD team, speak to your GP. If you can, speak to your IBD team before you start trying for a baby.[17]

Bowel Cancer Checks

Having ulcerative colitis that reaches beyond the rectum, or Crohn’s disease that affects your colon (the large bowel), can make bowel cancer more likely. Colitis that affects only the rectum (proctitis), and Crohn’s disease that doesn’t affect the colon, don’t raise this risk. Treatment has the best chance of working when bowel cancer is found early, and a regular check-up colonoscopy (surveillance colonoscopy) is the best way to find it early. Your first check is usually offered about 8 years after your symptoms started, or when you are diagnosed if you also have primary sclerosing cholangitis (PSC, a liver condition). Your IBD team should tell you when you need your checks.[18]

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Effects Outside the Gut (Extraintestinal Manifestations)

IBD can cause inflammation and symptoms in other parts of the body too. Doctors call these extraintestinal manifestations (EIMs), which simply means effects outside the gut. A review that pooled 52 studies involving more than 352,000 patients found that about 24% of all people with IBD experience at least one joint, skin or eye EIM, rising to 35% in Crohn’s disease and 27% in ulcerative colitis.[11]

EIMs can affect several parts of the body. The main sites include:

  • Joints: arthritis in the joints of the arms and legs (peripheral arthritis), and inflammation of the spine and the joints where the spine meets the pelvis (axial arthritis, including sacroiliitis and ankylosing spondylitis), are the most common
  • Skin: erythema nodosum (tender red nodules, typically on the shins) and pyoderma gangrenosum (deep, painful skin ulcers)
  • Eyes: inflammation inside the eye (uveitis) or of the white of the eye (episcleritis), which can cause eye pain, redness and blurred vision
  • Liver and bile ducts: primary sclerosing cholangitis (PSC), scarring of the tubes that carry bile from the liver, which occurs more commonly in ulcerative colitis

These effects can appear before IBD is diagnosed, during a flare or when your gut is settled, and they often need care from another specialist alongside your IBD (gastroenterology) team.

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If you’d like to read more about the topics above, these resources explain IBD in plain, everyday language. They’re written for patients and families rather than clinicians.

Understanding your condition

Health information for your country

Living with IBD and finding support

  • Travelling with IBD: Crohn’s & Colitis Australia, Crohn’s & Colitis UK and Crohn’s and Colitis Canada each have practical travel guides, covering things like travel insurance and vaccinations.
  • World IBD Day is a global awareness day (19 May) run by patient organisations in more than 50 countries, with personal stories and support for the millions of people living with IBD worldwide.

We look over this page at least once a year, and check phone numbers, opening hours and costs every month.

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References

  1. Alatab S, Sepanlou SG, Ikuta K, et al. The global, regional, and national burden of inflammatory bowel disease in 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet Gastroenterol Hepatol. 2020;5(1):17-30. doi:10.1016/S2468-1253(19)30333-4
  2. Baumgart DC, Sandborn WJ. Crohn’s disease. Lancet. 2012;380(9853):1590-1605. doi:10.1016/S0140-6736(12)60026-9
  3. Dolinger M, Torres J, Vermeire S. Crohn’s disease. Lancet. 2024;403(10432):1177-1191. doi:10.1016/S0140-6736(23)02586-2
  4. Le Berre C, Honap S, Peyrin-Biroulet L. Ulcerative colitis. Lancet. 2023;402(10401):571-584. doi:10.1016/S0140-6736(23)00966-2
  5. Danese S, Fiocchi C. Ulcerative colitis. N Engl J Med. 2011;365(18):1713-1725. doi:10.1056/NEJMra1102942
  6. Khor B, Gardet A, Xavier RJ. Genetics and pathogenesis of inflammatory bowel disease. Nature. 2011;474(7351):307-317. doi:10.1038/nature10209
  7. Crohn’s & Colitis UK. Crohn’s Disease. Accessed September 2026.
  8. Maaser C, Sturm A, Vavricka SR, et al. ECCO-ESGAR Guideline for Diagnostic Assessment in IBD Part 1: Initial diagnosis, monitoring of known IBD, detection of complications. J Crohns Colitis. 2019;13(2):144-164. doi:10.1093/ecco-jcc/jjy113
  9. Gordon H, Minozzi S, Kopylov U, et al. ECCO Guidelines on Therapeutics in Crohn’s Disease: Medical Treatment. J Crohns Colitis. 2024;18(10):1531-1555. doi:10.1093/ecco-jcc/jjae091
  10. Crohn’s & Colitis UK. Ulcerative Colitis. Accessed September 2026.
  11. Kilic Y, Kamal S, Jaffar F, Sriranganathan D, Quraishi MN, Segal JP. Prevalence of Extraintestinal Manifestations in Inflammatory Bowel Disease: A Systematic Review and Meta-analysis. Inflamm Bowel Dis. 2024;30(2):230-239. doi:10.1093/ibd/izad061
  12. Barberio B, Zamani M, Black CJ, Savarino EV, Ford AC. Prevalence of symptoms of anxiety and depression in patients with inflammatory bowel disease: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol. 2021;6(5):359-370. doi:10.1016/S2468-1253(21)00014-5
  13. Crohn’s & Colitis UK. Smoking or vaping and Crohn’s Disease, Ulcerative Colitis or Microscopic Colitis (IBD). Accessed September 2026.
  14. Crohn’s & Colitis UK. Food and Crohn’s or Colitis. Accessed September 2026.
  15. Crohn’s & Colitis UK. Precautions with immunosuppressants (PDF). 2023.
  16. Crohn’s & Colitis UK. Infliximab. Accessed September 2026.
  17. Crohn’s & Colitis UK. Pregnancy and birth with Crohn’s Disease or Ulcerative Colitis (IBD). Accessed September 2026.
  18. Crohn’s & Colitis UK. Risk of bowel cancer and other gut-related cancers. Accessed September 2026.
  19. NHS. Crohn’s disease. Accessed September 2026.
  20. NHS. Ulcerative colitis. Accessed September 2026.
  21. Crohn’s & Colitis UK. Surgery for Crohn’s Disease. Accessed September 2026.
  22. Crohn’s & Colitis UK. Surgery for Ulcerative Colitis. Accessed September 2026.
  23. Crohn’s & Colitis UK. Newly diagnosed with Crohn’s or Colitis. Accessed September 2026.
  24. Crohn’s & Colitis UK. Treatment information: 5-ASAs, steroids, azathioprine and mercaptopurine, methotrexate, adalimumab, vedolizumab, ustekinumab, risankizumab, tofacitinib and ozanimod. Accessed October 2026.
  25. Crohn’s & Colitis UK. Further changes to the shingles vaccination programme 2025 (which doses of IBD medicines count as immunosuppressed). Accessed October 2026.
  26. healthdirect. How to read Consumer Medicine Information (CMI). Accessed October 2026.
  27. Mind Over Gut (Associate Professor Simon Knowles, Swinburne University). About IBD.mindovergut.com. Accessed October 2026.