Crohn's Disease and Ulcerative Colitis: Two Forms of Inflammatory Bowel Disease

Crohn's disease and ulcerative colitis are the two main forms of inflammatory bowel disease, usually called IBD. Both cause genuine inflammation within the digestive tract, but they differ in where the inflammation occurs and how deeply it extends. Treatment aims first to control active inflammation, then to maintain remission and prevent complications.

What inflammatory bowel disease is Inflammatory bowel disease, usually shortened to IBD, is a group of long term conditions that cause inflammation within the digestive tract. The two main forms are Crohn's disease and ulcerative colitis. Both can cause diarrhoea, abdominal pain, fatigue, weight loss and bleeding from the bowel. IBD is immune mediated. The immune system responds inappropriately within the gut in someone with a combination of genetic and environmental susceptibility. IBD is not caused by poor hygiene, stress, personality or one particular food. Stress and diet can influence symptoms, but they do not explain the underlying inflammatory disease. IBD is not the same as IBS IBD and irritable bowel syndrome, usually called IBS, are different conditions despite their similar abbreviations. IBD causes measurable inflammation and may produce ulcers, bleeding, narrowing, fistulas or other structural damage within the digestive tract. IBS is a disorder of gut brain interaction and bowel function. It can cause significant pain, bloating, diarrhoea or constipation, but it does not cause the ulcerating inflammation characteristic of IBD. IBS does not turn into Crohn's disease or ulcerative colitis. A person can have IBS like symptoms alongside treated IBD, so continuing symptoms do not always mean that inflammation is active. Blood in the stool, unexplained weight loss, anaemia, fever, symptoms waking someone at night or abnormal inflammatory tests require assessment rather than being assumed to be IBS. What Crohn's disease is Crohn's disease can affect any part of the digestive tract from the mouth to the anus. The end of the small bowel, called the terminal ileum, and the colon are common sites. The mouth, stomach, upper small bowel and anal region can also be involved. Inflamed areas are often patchy, with sections of relatively normal bowel between them. These separated areas are sometimes called skip lesions. Crohn's inflammation can extend through the full thickness of the bowel wall. This deeper pattern helps explain strictures, fistulas, abscesses and perforation. Not every person develops every feature. Location, depth and behaviour are established through specialist investigation rather than symptoms alone. What ulcerative colitis is Ulcerative colitis affects the colon and rectum, which form the large bowel. Inflammation usually begins in the rectum and extends upwards through the colon in a continuous pattern. Disease limited to the rectum is called proctitis. Left sided colitis extends further through the left colon, while extensive colitis affects more of the colon. Ulcerative colitis mainly affects the mucosa, the innermost lining of the bowel. Ulcers can form within this inflamed surface and cause blood, mucus and urgency. Ulcerative colitis does not normally cause patchy full thickness inflammation throughout the digestive tract. Severe disease can still become life threatening. The comparison is useful but not absolute Crohn's disease is usually patchy, can affect any gastrointestinal site and can involve the full bowel wall. Ulcerative colitis is usually continuous from the rectum, limited to the colon and concentrated within the mucosal lining. These differences help clinicians classify IBD. They should not be used as a home diagnostic checklist. Early treatment, severe inflammation and previous surgery can alter appearances. Occasionally the available evidence cannot confidently separate Crohn's disease from ulcerative colitis. The term IBD unclassified may be used while the pattern becomes clearer. This does not mean that the illness is imaginary or that no treatment is possible. Common Crohn's disease symptoms Crohn's symptoms depend partly on the site and severity of inflammation. Common features include persistent or recurring diarrhoea, abdominal pain, fatigue, reduced appetite and unintentional weight loss. Blood or mucus may appear in the stool, particularly when the colon is involved. Crohn's affecting only the small bowel may cause little visible bleeding. Disease near the anus can cause pain, discharge, swelling, fissures, abscesses or fistulas. Narrowing of the bowel can produce cramping pain, abdominal swelling, nausea, vomiting or constipation rather than diarrhoea. Common ulcerative colitis symptoms Ulcerative colitis commonly causes recurring diarrhoea containing blood, mucus or pus. Inflammation in the rectum creates urgency, frequent bowel movements and the feeling of needing to pass stool even when little is present. Cramping abdominal pain may improve temporarily after opening the bowels. Severe or extensive inflammation can cause fever, rapid heartbeat, anaemia, weight loss and profound fatigue. Proctitis can sometimes cause rectal bleeding, mucus and urgency without frequent diarrhoea. The number of stools alone does not show the full severity. Bleeding, pulse, temperature, anaemia, hydration and general condition also matter. Flares and remission A flare is a period when inflammatory disease becomes more active. Remission means that symptoms and inflammatory activity are well controlled. Remission can be assessed through symptoms, blood or stool markers, endoscopy and imaging. Symptoms and inflammation do not always move together. A person may feel better while inflammation remains, or have bowel symptoms despite little active inflammation. This is why treatment decisions should not rely only on pain or stool frequency. Infection, bile acid diarrhoea, scar related narrowing, medicine effects and IBS like symptoms can all resemble an IBD flare. Extraintestinal manifestations IBD can cause inflammation outside the digestive tract. These problems are called extraintestinal manifestations. Joints may become painful, stiff or swollen. Some joint symptoms parallel bowel activity, while others follow a separate course. Eye inflammation can cause redness, pain, sensitivity to light or blurred vision. A painful red eye or visual change needs urgent same day assessment. Skin manifestations include tender red or darker nodules called erythema nodosum and deeper painful ulcers called pyoderma gangrenosum. Mouth ulcers, reduced bone strength and blood clots can also occur. These features require assessment because medicines, infection and unrelated conditions can produce similar symptoms. Liver and bile duct disease Primary sclerosing cholangitis, usually called PSC, is inflammation and scarring of the bile ducts. It is more strongly associated with ulcerative colitis but can occur with Crohn's colitis or without diagnosed IBD. PSC may initially cause no symptoms. Later features can include itching, fatigue, abdominal discomfort, fever or jaundice. Abnormal liver tests do not automatically mean PSC. Medicines, fatty liver, gallstones, infection and other liver conditions must also be considered. IBD care includes liver test monitoring when clinically appropriate. Anaemia and nutritional problems Ongoing bleeding can cause iron deficiency anaemia. Inflammation can also reduce iron availability and contribute to anaemia of chronic disease. Medicines and vitamin deficiencies are additional possibilities. Crohn's disease affecting the small bowel can reduce absorption of vitamin B12, folate, iron, vitamin D and other nutrients. Reduced intake, diarrhoea and previous bowel surgery can add to malnutrition risk. Children may show poor growth or delayed puberty before bowel symptoms become prominent. Growth and development must be monitored directly. Why diagnosis can take time No single symptom or test diagnoses every case of IBD. Diarrhoea and abdominal pain can result from infection, coeliac disease, bowel cancer, diverticular disease, medicine effects, microscopic colitis and IBS. The pattern may be mild, intermittent or located beyond the reach of a standard lower bowel examination. Clinicians combine what the person describes, examination, blood tests, stool tests, endoscopy, biopsies and imaging. A normal single test does not always end the investigation when the wider pattern remains concerning. Initial assessment The clinician asks about stool frequency, bleeding, mucus, urgency, night time symptoms and abdominal pain. They ask about fever, weight change, appetite, fatigue, mouth ulcers, joint symptoms, rashes and painful eyes. Family history, smoking, recent travel, antibiotics, infections and medicines are relevant. The examination may assess hydration, temperature, pulse, blood pressure, weight, abdominal tenderness and swelling. The anal region may need examination when pain, discharge, swelling or suspected fistula disease is present. Consent, privacy and a chaperone are important. Blood tests A full blood count can identify anaemia, high platelets or changes in white blood cells. C reactive protein and erythrocyte sedimentation rate can support evidence of inflammation. Normal values do not exclude localised or mild IBD. Kidney, liver, albumin, iron, vitamin B12, folate and vitamin D tests may be selected according to the presentation. Blood tests cannot reliably distinguish Crohn's disease from ulcerative colitis on their own. They are also used to assess severity and prepare safely for treatment. Stool tests and infection Stool samples may be tested for bacteria, parasites or Clostridioides difficile when infection is possible. A gastrointestinal infection can mimic IBD or trigger deterioration in someone with established disease. Starting or increasing immune suppression without considering infection can be dangerous. Blood or mucus in the stool should not be attributed automatically to infection, piles or IBD without appropriate assessment. Faecal calprotectin Faecal calprotectin is a protein released during inflammation within the intestine. A raised result supports the possibility of active intestinal inflammation and can help distinguish IBD from non inflammatory conditions such as IBS. It does not diagnose Crohn's disease or ulcerative colitis by itself. Infection, some medicines, bowel cancer and other inflammatory disorders can also raise it. A low result makes significant active intestinal inflammation less likely in an appropriate low risk setting. It does not safely override alarm symptoms or suspected cancer pathways. In established IBD, changing calprotectin levels can help assess inflammation and response to treatment. Endoscopy and biopsy Colonoscopy allows the rectum, colon and end of the small bowel to be examined. A flexible sigmoidoscopy examines the rectum and lower colon and may be used during severe colitis when a full colonoscopy would be unsafe. Small tissue samples called biopsies are taken even from areas that appear normal. Microscopy can identify chronic inflammation and help distinguish disease patterns. Upper gastrointestinal endoscopy may be needed when Crohn's disease affecting the mouth, oesophagus, stomach or upper small bowel is suspected. Endoscopy also helps assess healing and supports cancer surveillance. Imaging the small bowel and complications MRI enterography and intestinal ultrasound can show inflammation, narrowing, abscesses and disease beyond the reach of colonoscopy. CT may be used when rapid assessment is needed, particularly during an emergency. Pelvic MRI is important when perianal fistulas or abscesses are suspected. Capsule endoscopy uses a swallowed camera to inspect the small bowel in selected people. It may be unsafe when a stricture could trap the capsule. Imaging results require specialist interpretation alongside endoscopy and biopsy. Crohn's strictures and obstruction Repeated inflammation and healing can narrow a segment of bowel. This is called a stricture. A stricture may contain active inflammation, fixed scar tissue or both. The balance affects whether medicine, endoscopic treatment or surgery is most appropriate. Possible obstruction symptoms include wave like abdominal pain, swelling, vomiting and inability to pass stool or wind. Complete obstruction is an emergency. Antidiarrhoeal medicines or a high fibre diet can be unsafe when significant narrowing is present. Crohn's fistulas and abscesses A fistula is an abnormal tunnel connecting the bowel with another bowel loop, the skin, bladder, vagina or another structure. Perianal Crohn's disease can cause fistulas, fissures and abscesses around the anus. An abscess is a collection of infected fluid or pus. It may cause constant pain, fever, tenderness and systemic illness. Abscesses often require drainage and antibiotics. Immune modifying treatment alone does not drain an infected collection. Fistula management may combine imaging, surgery, antibiotics and biological treatment. Ulcerative colitis and toxic megacolon Acute severe ulcerative colitis is a medical emergency requiring hospital care. Severe inflammation can cause the colon to become enlarged and lose normal movement. This is called toxic megacolon. Possible features include increasing abdominal pain or swelling, fever, rapid heartbeat, bleeding and severe illness. The colon can perforate, causing peritonitis and sepsis. Treatment involves close medical and surgical review. Delaying hospital assessment or using bowel slowing medicines without advice can be dangerous. Bowel perforation and severe bleeding Full thickness Crohn's disease can rarely create a hole in the bowel wall. Severe ulcerative colitis can also lead to perforation. Sudden severe pain, a rigid or very tender abdomen, fever, collapse or rapidly worsening illness requires emergency assessment. Heavy or continuous rectal bleeding can cause shock and severe anaemia. Black stool may indicate bleeding higher in the digestive tract and requires urgent assessment. Blood clot risk Active IBD increases the risk of venous blood clots. Hospital admission, surgery, reduced mobility, pregnancy and some medicines may add further risk. A painful swollen leg may indicate deep vein thrombosis. Sudden breathlessness, chest pain, collapse or coughing blood may indicate pulmonary embolism. These symptoms require urgent or emergency assessment. The aims of treatment IBD treatment has two distinct but connected phases. Inducing remission means controlling an active flare and reducing inflammation promptly. Maintaining remission means continuing an effective strategy to prevent relapse, complications and further bowel damage. A medicine suitable for induction may be unsuitable for maintenance. Corticosteroids are the clearest example because they can control a flare but should not be used as long term maintenance treatment. Treatment is chosen according to disease type, location, severity, previous response, complications and personal circumstances. Inducing remission in ulcerative colitis Mild or moderate ulcerative colitis is commonly treated first with an aminosalicylate, also called a 5 ASA. Rectal suppositories or enemas deliver treatment directly to proctitis or left sided disease. Oral treatment may be added or used for more extensive inflammation. A time limited corticosteroid may be used when aminosalicylates are insufficient or unsuitable. Moderate or severe disease may require biological medicines or targeted oral medicines under specialist care. Acute severe ulcerative colitis requires hospital admission, intravenous corticosteroids and early joint review by gastroenterology and colorectal surgery. Maintaining remission in ulcerative colitis Aminosalicylates can be continued long term to maintain remission after mild or moderate ulcerative colitis. Azathioprine or mercaptopurine may be considered when repeated steroid requiring flares occur or aminosalicylates do not maintain control. Biological and targeted medicines may serve both induction and maintenance roles when moderate or severe disease responds to them. Steroids are not maintenance treatment. Repeated steroid courses signal that the long term strategy needs review. Adherence matters even when symptoms have settled because maintenance treatment reduces relapse risk. Inducing remission in Crohn's disease A conventional corticosteroid is a common induction treatment for active Crohn's disease. Budesonide may be used for selected ileal, ileocaecal or right sided disease when its more local action is appropriate. Exclusive enteral nutrition uses a nutritionally complete liquid formula and can induce remission without steroids. It is particularly important in children and young people because nutrition and growth are central concerns. Biological or targeted medicines may be used for moderate or severe disease, fistulising disease or illness not controlled by conventional treatment. Antibiotics are used for specific infections, abscesses or some perianal complications. They are not routine treatment for every Crohn's flare. Maintaining remission in Crohn's disease Maintenance treatment depends on relapse risk, previous therapy and disease behaviour. Options can include azathioprine, mercaptopurine, methotrexate, biological medicines or targeted oral treatments. A medicine that successfully induces remission may be continued when it also has an established maintenance role. Long term systemic corticosteroids should be avoided because they do not maintain remission safely and cause substantial harm. Monitoring aims to prevent both visible symptoms and progressive bowel damage. Immunomodulators, biologics and targeted medicines Thiopurines such as azathioprine and mercaptopurine reduce immune activity and may take weeks or months to work. Biological medicines target specific inflammatory pathways. Examples include tumour necrosis factor, integrin, interleukin 12 and interleukin 23 pathways. Targeted oral medicines include Janus kinase inhibitors and sphingosine 1 phosphate receptor modulators for selected disease patterns. Not every medicine is approved or suitable for both Crohn's disease and ulcerative colitis. Specialists consider infection, cancer, cardiovascular, clotting, pregnancy and organ risks before choosing treatment. Treatment safety and monitoring Immune modifying treatment can reduce the body's ability to control infection. Baseline assessment may include blood counts, kidney and liver tests, tuberculosis screening and hepatitis testing. Regular blood tests monitor treatment toxicity. The exact schedule depends on the medicine and individual risk. Vaccination should be reviewed before significant immune suppression where possible. Some live vaccines are unsuitable during particular treatments. Fever, severe sore throat, painful urination, spreading skin infection or new breathlessness requires prompt clinical advice. Surgery in Crohn's disease Surgery may remove a severely damaged or narrowed bowel segment, drain an abscess or manage a fistula. It can relieve obstruction, treat complications and improve quality of life. Surgery does not cure Crohn's disease because inflammation can recur elsewhere or near a surgical join. Postoperative monitoring and preventive treatment may therefore continue. Repeated removal of small bowel can reduce nutrient and fluid absorption, so bowel preservation is considered carefully. Surgery in ulcerative colitis Surgery may be required for uncontrolled bleeding, perforation, toxic megacolon, cancer risk or disease that remains severe despite medicines. A colectomy removes the colon, the organ affected by ulcerative colitis. Waste may pass through an ileostomy or through an internal ileoanal pouch constructed from small bowel. Ulcerative colitis cannot recur in a colon that has been removed. Pouch inflammation, surgical complications and some extraintestinal manifestations can still occur. Surgery is a treatment choice requiring detailed discussion rather than a failure by the person or care team. Diet and nutrition There is no single diet proven to cure IBD. During a flare, stricture or after surgery, temporary dietary changes may reduce symptoms or prevent obstruction. These plans should be individualised. Removing entire food groups without advice can worsen nutritional deficiency. A specialist dietitian can assess weight loss, growth, deficiencies, eating difficulties and the effect of bowel surgery. Enteral nutrition is a medical treatment in selected Crohn's disease, not simply a general exclusion diet. Smoking Smoking worsens Crohn's disease and increases the risk of flares, complications and surgery. Stopping smoking is an important part of Crohn's management. Smoking has a different epidemiological relationship with ulcerative colitis, but starting or continuing smoking is not a safe treatment. The cardiovascular, cancer and respiratory harms of smoking outweigh any apparent bowel effect. Pregnancy and reproductive planning Most people with well controlled IBD can have successful pregnancies. Active inflammation at conception and during pregnancy increases the risk of complications. Planning pregnancy during remission is therefore preferable where possible. Many IBD medicines can be continued, while some require advance withdrawal or replacement. A person should not stop treatment independently after a positive pregnancy test because an uncontrolled flare can also harm the pregnancy. Pre pregnancy planning should involve gastroenterology and maternity care, with surgical or fertility advice when relevant. Children and young people IBD can affect growth, nutrition, puberty, schooling and emotional development. Height, weight, growth rate and pubertal progress require regular monitoring. Crohn's disease may first present with poor growth, delayed puberty, mouth ulcers or perianal disease rather than prominent diarrhoea. Exclusive enteral nutrition is an important induction option in paediatric Crohn's disease. Care should transition gradually from paediatric to adult services. Bowel cancer surveillance Longstanding inflammation affecting a substantial part of the colon increases colorectal cancer risk. Risk depends on disease duration, extent, inflammatory activity, health problems in the family, previous abnormal cells and associated PSC. Specialist surveillance colonoscopy begins after a defined duration of colonic disease and continues at intervals based on individual risk. Proctitis alone does not carry the same surveillance approach as extensive colitis. New bleeding, weight loss or altered bowel symptoms still require assessment between scheduled surveillance examinations. Living with urgency and unpredictability Urgency, pain, fatigue and fear of incontinence can affect work, education, travel, relationships and social activity. Access to toilets, workplace adjustments and an individual flare plan can improve independence. An IBD nurse often provides advice between specialist appointments. Anxiety and depression can occur alongside active or controlled disease and deserve appropriate treatment. Psychological support does not imply that bowel inflammation is caused by emotion. Ongoing monitoring Monitoring includes symptoms, weight, blood tests, stool markers, endoscopy or imaging according to the disease pattern. Clinicians assess inflammation, nutrition, treatment toxicity, bone health, infection risk and cancer surveillance. A person in clinical remission may still need treatment and monitoring. New symptoms should not automatically be assumed to be an IBD flare. Infection, cancer, medicine toxicity and non inflammatory bowel disorders remain possible. What this lesson should not be used for This lesson cannot diagnose Crohn's disease, ulcerative colitis or IBS from symptoms alone. It cannot determine whether abdominal pain, diarrhoea or bleeding represents a flare, infection, obstruction, perforation or cancer. Do not use it to start steroids, increase immune suppression, take bowel slowing medicines during severe colitis or stop maintenance treatment. Seek medical assessment for persistent diarrhoea, blood or mucus in stool, weight loss or recurring abdominal pain, and urgent help for severe pain, heavy bleeding, dehydration or rapid deterioration.

Crohn's disease and ulcerative colitis both cause genuine inflammatory bowel damage, unlike IBS, which is a disorder of gut brain interaction without the ulcerating inflammation of IBD. Crohn's disease is usually patchy, can affect any gastrointestinal site and can extend through the bowel wall, while ulcerative colitis is usually continuous from the rectum, limited to the colon and mainly mucosal. Treatment first induces remission, then uses a separate long term strategy to maintain it.