Skip to main content

Health condition · Clinically reviewed

Crohn’s disease, a transmural inflammatory bowel disease.

Skip-lesion inflammation that can affect any part of the GI tract. Modern biologics and small molecules have transformed long-term outcomes.

Jump to treatment See red-flag symptoms
A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE, BSG and ECCO sources you can see at the end.

  • 03

    Current for 2026

    Reflects current UK guidance on Crohn’s disease — biologics, small molecules and surgical care.

Key facts

Crohn’s disease at a glance.

The essentials, in plain English — what it is, where it strikes, how it is diagnosed, and how it is treated in the UK today.

  • What it is

    A chronic transmural inflammatory bowel disease with characteristic skip lesions along the GI tract.

  • Where it strikes

    Anywhere from mouth to anus — the terminal ileum is the most commonly affected site.

  • How common

    UK prevalence around 1 in 500 — usually diagnosed in young adults.

  • Activity marker

    Faecal calprotectin is the standard non-invasive marker of active bowel inflammation.

  • Modern therapy

    Biologics and JAK inhibitors are central — often delivering deep, steroid-free remission.

  • When surgery

    Fistulising or stricturing disease may need surgery — resection is not curative but is often necessary.

Why this guide matters

A lifelong condition, a modern plan.

Crohn’s is chronic — but the therapy landscape has changed radically. The three points below shape everything else on this page.

  • Transmural, skip-lesion inflammation

    Crohn’s inflames the full bowel wall in patches — different in pattern from ulcerative colitis.

  • Biologics and small molecules changed it

    Anti-TNF, anti-integrin, anti-IL-12/23 and JAK inhibitors now deliver deep, steroid-free remission.

  • Surgery is common — and not curative

    Around half of people need surgery at some point, usually for stricturing or fistulising disease.

How the diagnosis is made

From first symptoms to a clear plan.

The steps a UK gastroenterology team will normally follow, in order — so you know what to expect and why.

  1. 01

    Recognising

    Symptom & smoking history

    Diarrhoea, weight loss, perianal disease and — importantly — a smoking history all shape the diagnosis.

  2. 02

    Recognising

    Bloods (FBC, CRP, ferritin)

    Anaemia, raised inflammatory markers and iron deficiency are typical findings at presentation.

  3. 03

    Recognising

    Faecal calprotectin

    A non-invasive stool test that quantifies bowel inflammation and helps triage who needs endoscopy.

  4. 04

    Confirming

    Ileocolonoscopy + biopsies

    The definitive test — visualises skip lesions and confirms Crohn’s histologically with granulomas on biopsy.

  5. 05

    Confirming

    MR enterography

    The best modality for small-bowel disease — maps disease extent, strictures and inflammation without radiation.

  6. 06

    Confirming

    Cross-sectional imaging

    CT or MRI pelvis if a fistula, collection or abscess is suspected — often needed before surgery.

  7. 07

    Managing

    IBD MDT

    Gastroenterology, colorectal surgery, radiology and IBD nurses agree the induction and maintenance plan together.

Typical timeline: 4–8 weeks from first appointment to a settled plan.

Symptoms

What Crohn’s disease feels like.

A pattern of diarrhoea, right-lower-quadrant pain, weight loss and — often — perianal disease, with clear red flags to act on.

  • Diarrhoea

    Chronic loose stool — often without visible blood, unlike ulcerative colitis.

  • Abdominal pain

    Cramping pain — often in the right lower quadrant reflecting terminal ileal disease.

  • Weight loss

    Unintended weight loss during a flare reflects systemic inflammation and malabsorption.

  • Fatigue

    A persistent, disabling tiredness common in active IBD.

  • Perianal disease

    Fistulae, skin tags, abscesses and fissures — a hallmark of Crohn’s.

  • Mouth ulcers

    Aphthous ulcers may flare alongside gut inflammation and often precede a diagnosis.

  • Extra-intestinal

    Skin (erythema nodosum), joints (arthralgia) and eyes (uveitis) can all be involved.

  • Red flag

    Severe abdominal pain with fever — call 999. Possible perforation or intra-abdominal abscess.

Treatment

How Crohn’s disease is treated in the UK.

A layered plan — steroids for flares, immunomodulators, biologics, small molecules and surgery for complications.

  • Corticosteroids for flare

    Prednisolone or budesonide for short-course induction — never used for maintenance.

  • Enteral nutrition (paediatric)

    Exclusive enteral nutrition is a first-line induction option in children — as effective as steroids without the side-effects.

  • Azathioprine / methotrexate

    Immunomodulators used to maintain steroid-free remission, often alongside a biologic.

  • Anti-TNF (infliximab, adalimumab)

    Injected or infused antibodies that block TNF — effective for luminal and fistulising Crohn’s.

  • Anti-integrin (vedolizumab)

    A gut-selective biologic with a favourable safety profile — used in moderate-to-severe disease.

  • Anti-IL-12/23 (ustekinumab, risankizumab)

    Modern biologics targeting IL-12/23 pathways — increasingly used first-line for Crohn’s.

  • JAK inhibitor (upadacitinib)

    An oral small molecule for moderate-to-severe Crohn’s when biologics have failed or are unsuitable.

  • Surgery for stricturing / fistulising

    Resection or strictureplasty — not curative but often essential for complications and quality of life.

What this guide is based on

The sources behind every claim on this page.

UK and European specialist society guidance, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your gastroenterologist knows your history and can tell you which parts apply to you. If in doubt, seek assessment — especially with any red-flag features.

  • NICE. Crohn’s disease: management (NG129).

  • British Society of Gastroenterology. IBD guidelines.

  • ECCO. European Crohn’s and Colitis Organisation IBD guidelines.

  • Crohn’s & Colitis UK. Patient information on Crohn’s disease.

Red flags

When to seek urgent help.

These are the patterns that need urgent assessment — from your IBD team, your GP or emergency care.

  • Perforation

    Sudden severe abdominal pain with peritonism — a surgical emergency requiring urgent imaging and theatre.

  • Bowel obstruction

    Stricturing disease can cause vomiting, colicky pain and distension — needs urgent assessment.

  • Fistulising disease

    Enterocutaneous, enterovesical or enteroenteric fistulae need combined medical and surgical planning.

  • Perianal abscess

    Perianal pain, swelling or fever needs same-day drainage — antibiotics alone are not enough.

  • Toxic megacolon

    Colonic dilatation with systemic toxicity — rare in Crohn’s but a surgical emergency.

  • Post-biologic infection

    Fever, cough or opportunistic infection (TB, PJP) on biologics — seek urgent review.

  • Post-operative complications

    Fever, worsening pain or wound issues after resection — call your surgical team.

  • Pregnancy planning

    Active Crohn’s at conception increases risk — plan pregnancy in remission with joint obstetric and IBD care.

  • Cancer surveillance

    Long-standing colonic Crohn’s increases colorectal cancer risk — surveillance colonoscopy is essential.

Living with it

A long-term condition, with modern tools to keep it quiet.

Four habits that make the biggest difference — adherence, monitoring, vaccines and using your IBD nurse.

A quiet reminder

Remission is not a reason to stop.

Maintenance therapy keeps you well — stopping it in remission is the commonest reason people relapse.

  1. 01 Adherence

    Take maintenance therapy every day

    Stopping biologics or immunomodulators in remission is the commonest cause of relapse.

  2. 02 Monitoring

    Calprotectin & bloods

    Regular non-invasive tests catch subclinical inflammation early — before symptoms return.

  3. 03 Vaccines

    Stay up to date

    Live vaccines are avoided on biologics; annual flu and pneumococcal boosters are recommended.

  4. 04 Support

    Use your IBD nurse

    The specialist nurse line is the fastest route to advice during a flare.

Frequently asked

Everything we get asked about Crohn’s disease.

Quick answers on diagnosis, biologics, small molecules, surgery and when to seek urgent help.

  • What is Crohn’s disease?

    A chronic inflammatory bowel disease that can affect any part of the gastrointestinal tract from mouth to anus. Inflammation is transmural (through the full bowel wall) and typically involves skip lesions with normal bowel in between affected segments.

  • How is Crohn’s different from ulcerative colitis?

    Crohn’s can affect any part of the GI tract with skip lesions and transmural inflammation, and often causes perianal disease. Ulcerative colitis is limited to the colon and rectum with continuous mucosal inflammation. The two are distinguished by endoscopy, biopsies and imaging.

  • How is Crohn’s diagnosed?

    A combination of symptoms, blood tests, faecal calprotectin and — definitively — ileocolonoscopy with biopsies. MR enterography maps small-bowel disease and cross-sectional imaging is added if fistulae or abscesses are suspected.

  • What are biologics and small molecules?

    Biologics are injected or infused antibodies (anti-TNF, anti-integrin, anti-IL-12/23) that block specific inflammatory pathways. Small molecules like JAK inhibitors are oral tablets that block similar pathways from inside the cell.

  • Do I need surgery?

    Around half of people with Crohn’s will need surgery at some point — usually for stricturing or fistulising disease. Resection is not curative but often essential for complications and quality of life.

  • When should I seek urgent help?

    Severe abdominal pain with fever, signs of bowel obstruction, perianal abscess, or new infection on biologics — contact your IBD team or call 999.

Related content

Keep reading.

WhatsApp Call us

Nearby in the library

More conditions to explore

Browse all →
Pulse Healthcare concierge

Send us your enquiry

A concierge service for UK private healthcare. We match you with the best vetted clinics and consultants in our network - they then contact you directly.

So we can match you to the right clinician close to you.

Confidential. We respond within one working day.