Inflammatory bowel disease is an umbrella term for long-term conditions in which the immune system causes inflammation in the digestive tract, and the two main types are Crohn’s disease and ulcerative colitis [1].
This page provides general information. It does not replace advice from a doctor or another qualified healthcare professional.
Inflammatory bowel disease is a term for long-term conditions in which the immune system causes inflammation in the digestive tract [1,6]. The immune system is the body’s defense against infection. In IBD it reacts abnormally and inflames the lining of the gut instead [6,7]. IBD is a group term, and almost everyone with it has one of two conditions [1].
Crohn’s disease. Inflammation can occur anywhere from the mouth to the anus, though it most often affects the lower small intestine and parts of the large intestine, and it extends deeper into the wall of the bowel [7,10]. That depth causes the complications specific to Crohn’s: narrowed sections that block food, and fistulas, which are abnormal tunnels between the bowel and another organ or the skin [7,10]. See the trialport guide to Crohn’s disease.
Ulcerative colitis. Inflammation affects only the inner surface of the large intestine, meaning the colon and rectum, and open sores can form on that lining [2,9]. Doctors describe it by how far it reaches back from the rectum: the rectum alone, the rectum and lower colon, the left side, or the whole colon [4]. Ulcerative colitis is roughly half of all IBD.
IBD unclassified. IBD unclassified, also called indeterminate colitis, is used when someone clearly has IBD but the picture does not settle into either condition [12,13]. It is given more often to children, around 80 percent of whom are later reclassified, and it is usually treated like ulcerative colitis [12].
The initials are close and the symptoms overlap, so the confusion is understandable. Irritable bowel syndrome is a group of symptoms occurring together, including repeated abdominal pain and changes in bowel movements, without any visible sign of damage or disease in the gut [8]. Doctors call it a disorder of gut-brain interaction, which can make the gut more sensitive and change how the bowel muscles contract [8]. About 12 percent of people in the United States have IBS [8].
IBD is different. The inflammation is real, it shows on tests, and it can damage the bowel over time, so the two need different treatment [1,2]. IBS is common and hard to live with, so this is not one being serious and the other not. They are different problems.
Research funded by Crohn’s & Colitis UK, using the records of 38.3 million people registered with family doctors, found 0.81 percent of the United Kingdom population, about 1 in 123, living with Crohn’s disease, ulcerative colitis or IBD unclassified, rising to 1 in 67 over 70 [11]. One United States study put national prevalence at 0.72 percent in 2018 [14], with an estimated 1 million people affected by Crohn’s disease and 600,000 to 900,000 by ulcerative colitis [6,7].
Those figures count diagnosed people, so the true number is probably higher. The same research found lower recorded rates in more deprived areas and in people who did not describe their ethnicity as white, and concluded that barriers to diagnosis likely explain most of the gap [11].
IBD remains most common in North America, Europe and Oceania [10,14]. Since 2000, new cases have risen sharply in parts of Africa, Asia and Latin America, where prevalence is still much lower, while forecasts from Canada and Scotland suggest 1 percent of their populations by 2030 [14].
No single cause has been found. Researchers describe four things working together [6,7].
An immune reaction that goes wrong. The immune system attacks bacteria that normally live in the gut, and the resulting inflammation is the disease [7].
Genes. A gene is an instruction inside a cell, passed down from parents. IBD runs in families, and having a parent, brother, sister or child with it makes it more likely [6,7]. No single faulty gene is responsible. Research has linked around 200 regions of the genetic code to IBD risk, and genes named in Crohn’s disease include NOD2, ATG16L1, IL23R and IRGM [7,10].
The microbiome, the mix of bacteria, viruses and fungi living in the gut, looks different in people with IBD [6,7].
Environment. Where and how people live appears to matter, part of why IBD has spread as more countries industrialized [7,14]. Smoking roughly doubles the chance of Crohn’s disease [7].
Stress and particular foods do not cause IBD, though they can worsen symptoms [10]. Nobody gives themselves this condition.
Symptoms depend on the type and where the inflammation sits. Most people have flares, when symptoms are active, separated by remission, when they fade, which can last weeks or years [6,7].
The main symptoms are diarrhea lasting longer than four weeks, abdominal pain, blood or mucus in stools, bleeding from the bottom, constant tiredness, and losing weight without trying [1]. Bleeding and an urgent need to open the bowels lean toward ulcerative colitis [6]. Weight loss and pain after eating lean toward Crohn’s disease [7]. Children may grow slowly or reach puberty late [6,7].
Inflammation elsewhere in the body surprises people. IBD can inflame the joints, skin, eyes, and liver and bile ducts, and mouth ulcers are also seen [2,6,7].
When to seek urgent help. Most IBD is managed in clinic appointments, and severe episodes are the exception. Call emergency services or go to an emergency department for severe abdominal pain, non-stop bleeding from the bottom, a large amount of blood, or vomiting blood or material that looks like coffee grounds [1]. Get urgent advice for a severe ulcerative colitis flare, which may need hospital treatment, and for signs of a blocked bowel in Crohn’s disease: severe cramping, a swollen abdomen and being unable to pass stool or wind [1,4,7].
Diagnosis usually starts with a family doctor arranging first tests, then moves to a gastroenterologist, a doctor specializing in the digestive system, often with a specialist nurse, dietitian and surgeon [1,4,6].
Blood tests look for anemia, meaning fewer red blood cells than normal, and markers of inflammation such as C-reactive protein [6,7].
Stool tests rule out infections and measure fecal calprotectin, which rises when the gut lining is inflamed. This is the most useful early test for telling IBD apart from irritable bowel syndrome, before any camera test [5,12].
Endoscopy with biopsy confirms the diagnosis. A colonoscopy passes a thin flexible tube with a camera through the bottom to view the large intestine, and tissue samples are checked under a microscope [6,7].
Imaging matters more in Crohn’s disease, since inflammation can sit where a colonoscopy cannot reach. MRI and CT scans are used, and a swallowed camera capsule can photograph the small bowel [7].
Diagnosis is often slow. A review of 31 studies found median delays between symptoms starting and diagnosis of two to about five months for IBD overall, and two to twelve months in three-quarters of the Crohn’s studies [17].
There is no cure, but treatment is effective. The aim is to settle the inflammation, then keep it settled [6,7]. Guidelines call these two jobs inducing and maintaining remission, and often use different medicines for each [3,4].
Aminosalicylates reduce inflammation in the bowel lining and are the first treatment for mild to moderate ulcerative colitis, as tablets, as an enema or suppository, or both [4]. They play a much smaller part in Crohn’s disease [3].
Corticosteroids, usually called steroids, settle a flare. Both guidelines are clear that they are for time-limited courses only and not for keeping people well, since long-term use causes serious side effects [3,4,6].
Immunomodulators such as azathioprine, mercaptopurine and methotrexate damp down the immune system. They work slowly, so they hold remission rather than rescue a flare, and need regular blood monitoring [3,4].
Biologics are made from living cells and block one specific part of the inflammatory process. Infliximab, adalimumab, ustekinumab and vedolizumab are used in Crohn’s disease, and biologics are also used in moderately to severely active ulcerative colitis [3,4].
Small-molecule medicines are newer tablets acting inside cells, including Janus kinase inhibitors used in ulcerative colitis [4,6].
Surgery is not a failure of treatment. Between 30 and 55 percent of people with Crohn’s disease need an operation within ten years, usually to remove a damaged or narrowed section [7]. In ulcerative colitis, removing the colon and rectum ends the disease itself, with waste collected through a stoma or an internal pouch made from the small intestine [2,6].
On food. No specific food has been shown to cause IBD or to worsen it for everyone, and no diet should be started or stopped without the care team [6,7]. One exception is well established: in children with active Crohn’s disease, taking all nutrition as a special liquid feed for six to eight weeks, called exclusive enteral nutrition, is recommended by European specialist guidelines as the first treatment, ahead of steroids, because it also supports growth [3,15].
Only a local care team can say what is available where someone lives.
Fatigue is the symptom people most often say is underestimated. A review of 20 studies found about 47 percent of adults with IBD had fatigue, rising to 72 percent in active disease and still 47 percent in remission [16]. Feeling exhausted when tests say the inflammation has settled is common, not imagined.
Stress, anxiety and low mood are commonly reported by people with Crohn’s disease, and stress may worsen symptoms [7]. Asking for psychological support is a normal part of IBD care.
Practical things help: knowing where toilets are, telling an employer or school enough to arrange flexibility, and having a written plan for a flare. Check-ups continue during remission, and people with long-standing disease in the large intestine are offered periodic colonoscopy to watch for changes linked to bowel cancer [4,6]. Steroids and inflammation can weaken bones, so bone health is monitored in some people [3,6]. In pregnancy, guidelines ask the gut and maternity teams to share care, with medicines discussed before conception [3,4].
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:
IBD studies often ask for samples between visits and a daily symptom record. That record is real work, and it is fair to ask how long it takes each day.
Every trial has rules about who can take part, called eligibility criteria. For an IBD study they might include a confirmed diagnosis of Crohn’s disease or ulcerative colitis rather than IBD unclassified, a disease activity score inside a set range, inflammation visible at a recent colonoscopy, a fecal calprotectin level above a threshold, 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 inflammatory bowel 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 and what is being studied changes, so this list will date. For current information, search at app.trialport.com.
In the United Kingdom, Crohn’s & Colitis UK runs a helpline and covers symptoms, treatments, work and benefits [1,11], and the NHS pages on inflammatory bowel disease set out when to seek help [1].
In the United States, the Crohn’s & Colitis Foundation covers education, support and research [13], and the NIDDK pages on Crohn’s disease and ulcerative colitis give detailed government-reviewed explanations [6,7].
Crohn’s & Colitis Australia has one of the few good patient explanations of IBD unclassified [12].
Coverage is thinner elsewhere, and a hospital gastroenterology team is the best starting point.
Is IBD the same as IBS?
No. IBS causes similar symptoms without visible inflammation or damage, and needs different treatment [2,8]. A stool test for fecal calprotectin helps tell them apart [5].
Does it matter whether I have Crohn’s disease or ulcerative colitis?
Yes, for treatment. The medicines, the parts of the gut involved and the type of surgery differ [3,4]. For a minority the picture is unclear at first, and IBD unclassified is used until it settles [12,13].
Did something I ate cause this?
No food has been shown to cause IBD, though foods can worsen symptoms for individuals. A food diary agreed with the care team is the way to find personal triggers [6,7].
Will I need surgery?
Not necessarily. Between 30 and 55 percent of people with Crohn’s disease have an operation within ten years [7]. In ulcerative colitis, surgery is offered when medicines are not controlling the disease or there are serious complications [6].
Can IBD be cured?
Medicines do not cure it, and treatment aims to bring on and hold remission [6,7]. Removing the colon and rectum ends ulcerative colitis itself, but it is major surgery with lasting consequences [2,6].
Why do my joints, eyes or skin hurt when my gut flares?
Inflammation beyond the bowel is a recognized part of IBD [6,7]. Report it to the gut team, not to separate services.
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