Crohn’s disease is a long-term condition in which the immune system inflames the digestive tract, anywhere from the mouth to the anus, and the inflammation reaches through the whole thickness of the bowel wall [2,3].
This page provides general information. It does not replace advice from a doctor or another qualified healthcare professional.
Crohn’s disease is a long-term condition in which the immune system, the body’s defense against infection, inflames the digestive tract. It turns on bacteria that normally live in the gut, and the resulting inflammation is the disease [2,5].
Crohn’s is one of two main types of inflammatory bowel disease. For how it differs from ulcerative colitis, and why neither is irritable bowel syndrome, see the trialport guide to inflammatory bowel disease.
Two things set it apart.
It can appear anywhere from the mouth to the anus, most often in the lower small intestine and the start of the large intestine, in patches with healthy gut in between [2,3,5].
It reaches through the whole thickness of the bowel wall. Inflammation that breaks through the outer layers can create an abscess, a pocket of pus, or a fistula, a tunnel between the bowel and another organ or the skin. Scarring can narrow a section, called a stricture [1,2,5]. Ulcerative colitis inflames only the inner lining of the large intestine, which is why these problems belong to Crohn’s [3].
Symptoms follow the location: indigestion-like pain higher up, pain and bloating in the small bowel, diarrhea with blood or mucus in the large bowel, and separate problems around the anus [5].
Records of more than 38.3 million people registered with family doctors in the United Kingdom showed 0.3 percent had a recorded diagnosis of Crohn’s in 2020, roughly 1 in 333 [6]. Estimates for the United States range from more than half a million to around 1 million [2,3]. All count recorded diagnoses, so the true number is probably higher. Crohn’s is more common in people of northern European and Ashkenazi Jewish descent, and rates are rising for reasons experts do not know [2,3].
No single cause has been found. Several things act together [2,5].
The immune reaction. The protective barrier lining the gut appears to be faulty, so the immune system attacks bacteria and viruses that normally live there [5].
Genes. A gene is an instruction inside a cell, passed down from parents. Crohn’s is not inherited in a simple pattern and no single faulty gene is responsible. At least 200 genetic variations influence the risk, many in genes helping the immune system respond to gut bacteria [3]. About 15 percent of people with Crohn’s have a close relative who also has it, though most relatives never develop it [3,5].
The environment. Smoking roughly doubles the chance of developing Crohn’s and appears to play a part in flare-ups [2,3]. One large study found current smokers had a higher risk of Crohn’s and a lower risk of ulcerative colitis, so the two conditions point in opposite directions on this factor [18]. Stopping smoking is part of Crohn’s care, and stopping before surgery lowers the chance of needing further operations [4,5].
Nothing a person ate or did brought this on. No food has been shown to cause Crohn’s, and stress does not cause it, although stress may worsen symptoms [2,5].
The most common symptoms are diarrhea, cramping and pain in the abdomen, and weight loss [2]. Many people also have urgency, extreme tiredness, fever, loss of appetite, anemia, joint pain, sore eyes or skin changes [1,2,5]. Symptoms most often start in the teens or twenties, though Crohn’s can begin at any age, and in children it may slow growth or delay puberty [1,2,3]. Active periods are called flare-ups and quieter ones remission, which can last weeks or years [2].
Crohn’s often affects the area around the anus, and this is the part people are least likely to raise.
Around 1 in 3 people with Crohn’s develop a fistula, most often near the anus. It causes a sore swelling, and the pain can worsen when sitting, moving, passing stool or coughing [5]. Other perianal problems include fissures, small tears that cause pain and bleeding, skin tags, and abscesses, swollen pus-filled pockets that can cause a fever [5]. In one large study of children with Crohn’s, 21 percent developed perianal disease [19]. Some people notice these before anything else in the gut [5].
Urgency, needing a toilet in a hurry, is a recognized symptom rather than a personal failing. Crohn’s & Colitis UK provides a Can’t Wait Card and an accessible-toilet key for exactly this reason [1,5].
Gut teams ask about pain, bleeding and problems around the bottom routinely [5]. Nothing here is unusual to them, and treatment exists for all of it.
When to seek urgent help. Emergencies are the exception. Ask for an urgent appointment or call an out-of-hours service if stool is black or dark red, or if there is bloody diarrhea [1]. Severe cramping with vomiting and a swollen, distended abdomen can mean a blocked bowel [5]. A painful, swollen abscess with a fever also needs prompt help, since it may need draining and antibiotics [2,5].
Diagnosis usually starts with a family doctor arranging blood and stool tests, then a referral to a gastroenterologist, a specialist in the digestive system [1].
Blood tests look for anemia, fewer red blood cells than normal, and C-reactive protein, which rises with inflammation [2]. Stool tests rule out infection and measure fecal calprotectin, which rises when the gut lining is inflamed [5].
Endoscopy with biopsy confirms the diagnosis most reliably. A thin flexible tube with a camera passes through the bottom or the mouth, and small tissue samples are examined under a microscope [2,5].
Imaging and capsule endoscopy reach what a colonoscopy cannot. Magnetic resonance enterography, an MRI of the small bowel, is a first-line investigation in newly diagnosed Crohn’s, and CT and ultrasound are also used [2,5,21]. A swallowed capsule with a tiny camera can photograph the small intestine [2].
Diagnosis is often slow, since there is no single test and symptoms overlap with other gut conditions [1]. Three-quarters of the Crohn’s studies in one review reported a median delay of 2 to 12 months from first symptoms to diagnosis [8].
There is no cure, and treatment is still effective. It works in two steps: settling an active flare, called inducing remission, then keeping the condition quiet, called maintaining remission [4,5].
Corticosteroids, usually called steroids, settle a flare quickly. Guidance in England offers one such as prednisolone for a first presentation or a single flare in 12 months, and is explicit that steroids must not be used to maintain remission, since long-term use causes serious side effects [2,4].
Immunomodulators such as azathioprine, mercaptopurine and methotrexate damp down the immune response. They hold remission rather than rescue a flare [4].
Biologics and other targeted medicines each block one part of the inflammatory process. Infliximab and adalimumab block tumor necrosis factor alpha [10]. Vedolizumab blocks alpha-4-beta-7 integrin, found mostly on white blood cells in the gut [11]. Ustekinumab blocks interleukin 12 and 23 [12], risankizumab blocks interleukin 23 [13], and upadacitinib is a tablet blocking enzymes called Janus kinases [14]. In England the last two follow an earlier biological treatment that did not work well enough, stopped working or was not tolerated [15,16]. Availability differs between countries.
Aiming at a target. Specialists set short-term targets of symptom relief and normal blood and stool markers, and long-term targets of remission and endoscopic healing, meaning the gut lining looks healed at a camera test [7].
Liquid feed in children. Children with active Crohn’s are usually treated first with a liquid-only diet for six to eight weeks, which provides all the nutrients they need while the gut settles [5]. Guidance in England says to consider it instead of a steroid where growth or side effects are a concern [4].
Surgery is common, and it is not a failure. Between 30 and 55 percent of people have an operation within 10 years of diagnosis [2]. Operations include removing a damaged section of bowel, widening a narrowed one, and forming a stoma, an opening on the abdomen where waste passes into a bag [2,5]. Surgery relieves complications, and it does not cure Crohn’s, since inflammation can return elsewhere [1,2]. Ulcerative colitis differs, since removing the colon and rectum ends the need for lifelong medicines [17].
Fatigue is real. A meta-analysis of 20 studies found 47 percent of adults with inflammatory bowel disease had fatigue, rising to 72 percent during active disease [9]. Feeling exhausted when tests say the inflammation has settled is common, not imagined.
Mental health. People with Crohn’s or colitis may be twice as likely to experience anxiety or depression, and harder periods cluster around diagnosis, flare-ups, hospital stays and steroid courses [5].
Fertility and pregnancy. Fertility is likely similar to anyone else’s when Crohn’s is well controlled, and active disease can make conception harder [5]. Speak to a specialist before trying for a baby, since some medicines are unsuitable in pregnancy and some affect male fertility [1,4].
Nutrition and vitamin B12. Vitamin B12 is absorbed at the very end of the small bowel, so people who have had that section removed, or who have inflammation there, may need B12 injections. Iron and calcium shortages are also common [5].
Work, school and daily life. Guidance asks care teams to support body image and attendance at school and university [4]. In the United Kingdom, Crohn’s may count as a disability under the Equality Act 2010, depending on its effect on daily life [5].
Clinical trials test whether a treatment works and is safe. Deciding whether to look into one is personal, and it helps to take it in steps.
It is worth being clear on what a study involves:
Crohn’s studies often ask for stool samples between visits and a daily symptom record. That record is real work, and it is fair to ask how many minutes a day it takes.
Every trial has rules about who can take part, called eligibility criteria. For a Crohn’s study they might include a confirmed diagnosis rather than unclassified inflammatory bowel disease, a disease activity score inside a set range, ulcers visible at a recent colonoscopy, a fecal calprotectin level above a threshold, no stricture or untreated abscess, a stable dose of current treatment beforehand, or having already tried a particular class of medicine.
trialport’s medifit helps people consider information related to possible medical suitability. It does not diagnose a condition, confirm eligibility or replace formal screening by the study team.
Explore Crohn’s disease clinical trials through trialport
A study can look right on paper and still be hard in practice. Worth thinking through:
trialport’s readifit helps people reflect on their understanding, motivation, time, routines, support, emotions and practical arrangements.
Useful questions to put to a research team:
Taking part is voluntary. A person can ask questions, speak with people they trust and choose not to participate.
Search for clinical trials at app.trialport.com.
Study status checked: 3 August 2026. Research moves quickly, so this list will date. For current information, search at app.trialport.com.
In the United Kingdom, Crohn’s & Colitis UK runs a helpline on 0300 222 5700 and publishes evidence-based information on treatments, surgery, mental health, work and money, plus a Can’t Wait Card and an accessible-toilet key [1,5]. The NHS pages on Crohn’s disease cover symptoms, tests and when to seek help [1]. CICRA supports children with Crohn’s and their families [1].
In the United States, the NIDDK pages on Crohn’s disease give a government-reviewed explanation [2], and MedlinePlus Genetics covers the genetics [3]. The European Medicines Agency publishes a plain-language overview of each approved medicine [10,11]. Coverage is thinner elsewhere, and a hospital gastroenterology team is the best starting point.
Amy Dowden, the professional dancer known to television audiences from Strictly Come Dancing, is an ambassador for Crohn’s & Colitis UK. She has described bouts of illness beginning at age 11 and a bad flare at 19 that led to tests confirming Crohn’s. “It was such a relief to finally receive a diagnosis,” she said [20].
Is Crohn’s disease the same as ulcerative colitis?
No. Crohn’s can appear anywhere from the mouth to the anus and inflames the full thickness of the bowel wall, while ulcerative colitis inflames only the inner lining of the large intestine [2,3]. The trialport guide to inflammatory bowel disease compares them.
Did something I ate, or stress, cause this?
No food has been shown to cause Crohn’s, and stress does not cause it either, although both can worsen symptoms for individuals [2,5].
Should I mention pain, bleeding or a swelling around my bottom?
Yes, as early as possible. Around 1 in 3 people with Crohn’s develop a fistula, and anal or perianal fistulas are the most common kind [5]. Gut teams ask about this routinely, and there are treatments for all of it.
Will I need surgery, and would it cure me?
Between 30 and 55 percent have an operation within 10 years of diagnosis [2]. Surgery treats complications and can greatly improve symptoms, and it does not cure Crohn’s [1,2].
Does smoking really make that much difference?
Yes. Smoking roughly doubles the chance of developing Crohn’s, is linked to flare-ups, and raises the chance of needing further operations after surgery [2,3,5]. The association runs the other way in ulcerative colitis [18].
Why am I still exhausted when my tests look fine?
Fatigue affected 47 percent of adults with inflammatory bowel disease in a meta-analysis of 20 studies, and it was still 47 percent among people in remission [9]. Raise it with the care team.
Written by: trialport editorial team
Reviewed by: Keith Berelowitz, Founder and CEO, trialport
Reviewed on: 3 August 2026
Next review due: 3 August 2027
References last checked: 3 August 2026