Inflammatory bowel disease (IBD), which includes Crohn disease and ulcerative colitis, is a group of relapsing and remitting conditions characterized by chronic inflammation at various sites in the gastrointestinal tract, which results in diarrhea and abdominal pain.
Inflammation results from a cell-mediated immune response in the gastrointestinal mucosa. The precise etiology of inflammatory bowel disease is unknown, but evidence suggests that the normal intestinal flora inappropriately trigger an immune reaction in patients with a multifactorial genetic predisposition (perhaps involving abnormal epithelial barriers and mucosal immune defenses) (1). No specific environmental, dietary, or infectious causes have been identified, although epidemiologic risk factors have been identified (see Epidemiology, below). The immune reaction involves the release of inflammatory mediators, including cytokines, interleukins, and tumor necrosis factor.
Although Crohn disease and ulcerative colitis are similar, they can be distinguished in most cases (see table ). Approximately 5 to 11% of colitis cases are not distinguishable and are termed unclassified; if a surgical pathologic specimen cannot be classified, it is termed inflammatory bowel disease-unclassified (2–4). The term colitis applies only to inflammatory disease of the colon (eg, ulcerative, granulomatous, ischemic, radiation-induced, infectious). Spastic (mucous) colitis is a misnomer sometimes applied to a functional disorder, irritable bowel syndrome.
Differentiating Crohn Disease and Ulcerative Colitis
Crohn Disease | Ulcerative Colitis |
|---|---|
Small bowel is involved in 80% of cases.* | Disease is confined to the colon. |
Rectum is often spared; colonic involvement is usually right-sided. | Rectum is invariably involved; colonic involvement is usually left-sided. |
Gross rectal bleeding is rare overall, except in Crohn colitis. | Gross rectal bleeding is always present. |
Fistula, mass, and abscess development is common. | Fistulas do not occur. |
Perianal lesions are significant in approximately 20–25% of cases.†, ‡, § | Significant perianal lesions never occur. |
On imaging, bowel wall is affected asymmetrically and segmentally, with skip areas between diseased segments. | Bowel wall is affected symmetrically and uninterruptedly from rectum proximally. |
Endoscopic appearance is patchy, with discrete ulcerations separated by segments of normal-appearing mucosa. | Inflammation is uniform and diffuse. |
Microscopic inflammation and fissuring extend transmurally; lesions are often highly focal in distribution. | Inflammation is confined to mucosa except in severe cases. |
Epithelioid (sarcoid-like) granulomas are detected in bowel wall or lymph nodes in ≤ 20% of cases (pathognomonic when found).¶ | Typical epithelioid granulomas do not occur. |
* Data from Esaki M, Sakata Y. Clinical Impact of Endoscopic Evaluation of the Small Bowel in Crohn's Disease. Digestion. 2023;104(1):51-57. doi:10.1159/000527352 † Data from Everhov ÅH, Sachs MC, Malmborg P, et al. Changes in inflammatory bowel disease subtype during follow-up and over time in 44,302 patients. Scand J Gastroenterol. 2019;54(1):55-63. doi:10.1080/00365521.2018.15643611 ‡ Data from Dolinger M, Torres J, Vermeire S. Crohn's disease. Lancet. 2024;403(10432):1177-1191. doi:10.1016/S0140-6736(23)02586-2 § Data from Tsai L, McCurdy JD, Ma C, Jairath V, Singh S. Epidemiology and Natural History of Perianal Crohn's Disease: A Systematic Review and Meta-Analysis of Population-Based Cohorts. Inflamm Bowel Dis. 2022;28(10):1477-1484. doi:10.1093/ibd/izab287 ¶ Data from Johnson CM, Hartman DJ, Ramos-Rivers C, et al. Epithelioid Granulomas Associate With Increased Severity and Progression of Crohn's Disease, Based on 6-Year Follow-Up. Clin Gastroenterol Hepatol. 2018;16(6):900-907.e1. doi:10.1016/j.cgh.2017.12.034 | |
General references
1. Chang JT. Pathophysiology of Inflammatory Bowel Diseases. N Engl J Med. 2020;383(27):2652-2664. doi:10.1056/NEJMra2002697
2. Burisch J, Zammit SC, Ellul P, et al. Disease course of inflammatory bowel disease unclassified in a European population-based inception cohort: An Epi-IBD study. J Gastroenterol Hepatol. 2019;34(6):996-1003. doi:10.1111/jgh.14563
3. Everhov ÅH, Sachs MC, Malmborg P, et al. Changes in inflammatory bowel disease subtype during follow-up and over time in 44,302 patients. Scand J Gastroenterol. 2019;54(1):55-63. doi:10.1080/00365521.2018.15643611
4. Winter DA, Karolewska-Bochenek K, Lazowska-Przeorek I, et al. Pediatric IBD-unclassified Is Less Common than Previously Reported; Results of an 8-Year Audit of the EUROKIDS Registry. Inflamm Bowel Dis. 2015;21(9):2145-2153. doi:10.1097/MIB.0000000000000483
Epidemiology
Inflammatory bowel disease (IBD) is estimated to affect approximately 0.7% of the United States population, and approximately 0.3% in the overall North American, Oceanic, and European populations (1). The peak incidence is between 15 and 30 years of age (2–4). IBD may have a second smaller peak between ages 50 and 70; however, this later peak may include some cases of ischemic colitis.
IBD is most common among people of North America and Northern Europe (2). It is 2 to 4 times more common among people of Ashkenazi Jewish ancestry from Central or Eastern Europe than among non-Jewish White people from the same geographic location (5). The incidence is lower in eastern and southern Europe (6, 7) than in western and northern Europe, and lower still in South America, Asia, and Africa. However, the incidence is increasing among Black and Latin American people living in North America. Both sexes are roughly equally affected, although there may be differences specific to age, geographic region, and ulcerative colitis versus Crohn disease (8, 9). First-degree relatives of patients with IBD have a 4- to 20-fold increased risk; their absolute risk is approximately 5 to 7% (10, 11). Familial tendency is much higher in Crohn disease than in ulcerative colitis. Several gene mutations conferring a higher risk of Crohn disease (and some possibly related to ulcerative colitis) have been identified.
Risk factors for inflammatory bowel disease include a history of cigarette smoking, current oral contraceptive use, urban living, exposure to antibiotics in childhood, and vitamin D deficiency (Risk factors for inflammatory bowel disease include a history of cigarette smoking, current oral contraceptive use, urban living, exposure to antibiotics in childhood, and vitamin D deficiency (12, 13). Other factors, such as breastfeeding, Helicobacter pylori infection, and a high folate level, appear to be protective.
Current cigarette smoking seems to contribute to development or exacerbation of Crohn disease but decreases risk of ulcerative colitis (12, 13). Appendectomy performed to treat appendicitis also appears to lower the risk of ulcerative colitis but may be a risk factor for Crohn disease. Nonsteroidal anti-inflammatory drugs (NSAIDs) may exacerbate IBD.
Epidemiology references
1. Ng SC, Shi HY, Hamidi N, et al. Worldwide incidence and prevalence of inflammatory bowel disease in the 21st century: a systematic review of population-based studies. Lancet. 2017;390(10114):2769-2778. doi:10.1016/S0140-6736(17)32448-0
2. Lewis JD, Parlett LE, Jonsson Funk ML, et al. Incidence, Prevalence, and Racial and Ethnic Distribution of Inflammatory Bowel Disease in the United States. Gastroenterology. 2023;165(5):1197-1205.e2. doi:10.1053/j.gastro.2023.07.003
3. Abraham C, Cho JH. Inflammatory bowel disease. N Engl J Med. 2009;361(21):2066-2078. doi:10.1056/NEJMra0804647
4. Dolinger M, Torres J, Vermeire S. Crohn's disease. Lancet. 2024;403(10432):1177-1191. doi:10.1016/S0140-6736(23)02586-2
5. Schiff ER, Frampton M, Semplici F, et al. A new look at familial risk of inflammatory bowel disease in the Ashkenazi Jewish population. Dig Dis Sci. 63(11):3049-3057, 2018. doi: 10.1007/s10620-018-5219-9
6. Shivananda S, Lennard-Jones J, Logan R, et al. Incidence of inflammatory bowel disease across Europe: is there a difference between north and south? Results of the European Collaborative Study on Inflammatory Bowel Disease (EC-IBD). Gut. 1996;39(5):690-697. doi:10.1136/gut.39.5.690
7. Burisch J, Pedersen N, Čuković-Čavka S, et al. East-West gradient in the incidence of inflammatory bowel disease in Europe: the ECCO-EpiCom inception cohort. Gut. 2014;63(4):588-597. doi:10.1136/gutjnl-2013-304636
8. Shah SC, Khalili H, Gower-Rousseau C, et al. Sex-Based Differences in Incidence of Inflammatory Bowel Diseases-Pooled Analysis of Population-Based Studies From Western Countries. Gastroenterology. 2018;155(4):1079-1089.e3. doi:10.1053/j.gastro.2018.06.043
9. Shah SC, Khalili H, Chen CY, et al. Sex-based differences in the incidence of inflammatory bowel diseases-pooled analysis of population-based studies from the Asia-Pacific region. Aliment Pharmacol Ther. 2019;49(7):904-911. doi:10.1111/apt.15178
10. Podolsky DK. Inflammatory bowel disease. N Engl J Med. 2002;347(6):417-429. doi:10.1056/NEJMra020831
11. Rufo PA, Denson LA, Sylvester FA, et al. Health supervision in the management of children and adolescents with IBD: NASPGHAN recommendations. J Pediatr Gastroenterol Nutr. 2012;55(1):93-108. doi:10.1097/MPG.0b013e31825959b8
12. van der Sloot KWJ, Amini M, Peters V, Dijkstra G, Alizadeh BZ. Inflammatory Bowel Diseases: Review of Known Environmental Protective and Risk Factors Involved. Inflamm Bowel Dis. 2017;23(9):1499-1509. doi:10.1097/MIB.0000000000001217
13. Piovani D, Danese S, Peyrin-Biroulet L, Nikolopoulos GK, Lytras T, Bonovas S. Environmental Risk Factors for Inflammatory Bowel Diseases: An Umbrella Review of Meta-analyses. Gastroenterology. 2019;157(3):647-659.e4. doi:10.1053/j.gastro.2019.04.016
Extraintestinal Manifestations of Inflammatory Bowel Disease
Crohn disease and ulcerative colitis both affect organs other than the intestines. Most extraintestinal manifestations are more common in ulcerative colitis and Crohn colitis than in Crohn disease limited to the small bowel. Extraintestinal manifestations of inflammatory bowel disease are categorized in 3 ways:
1. Manifestations that usually parallel (ie, wax and wane with) intestinal inflammation: These disorders include peripheral arthritis, episcleritis, aphthous stomatitis, and erythema nodosum. Arthritis tends to involve large joints and be migratory and transient.
2. Disorders that are associated with IBD but appear independently of IBD activity: These disorders include ankylosing spondylitis, sacroiliitis, uveitis, pyoderma gangrenosum, and primary sclerosing cholangitis. Ankylosing spondylitis occurs more commonly in IBD patients with human leukocyte antigen B27 (HLA-B27). Most patients with spinal or sacroiliac involvement have evidence of uveitis and vice versa. Primary sclerosing cholangitis, which is a risk factor for cancer of the biliary tract, is strongly associated with ulcerative colitis and Crohn colitis. Cholangitis may appear before or concurrently with the bowel disease or even 20 years after colectomy. Liver disease (eg, most commonly fatty liver disease, but also autoimmune hepatitis, pericholangitis, and cirrhosis) occurs in about one-quarter of patients with IBD (1, 2). Some of these conditions (eg, primary sclerosing cholangitis) may precede IBD by many years and, when diagnosed, should prompt an evaluation for IBD.
3. Manifestations that are consequences of disrupted bowel physiology: These complications occur mainly in severe Crohn disease of the small bowel. Malabsorption may result from extensive ileal resection and cause deficiencies of fat-soluble vitamins, vitamin B12, or minerals, resulting in anemia, hypocalcemia, hypomagnesemia, clotting disorders, and bone demineralization. In children, malabsorption retards growth and development. Other complications include kidney stones resulting from excessive dietary oxalate absorption, hydroureter and hydronephrosis resulting from ureteral compression by the intestinal inflammatory process, gallstones resulting from impaired ileal reabsorption of bile salts, and amyloidosis secondary to long-standing inflammatory and suppurative disease.
Thromboembolic disease may occur as a result of multiple factors in all 3 categories.
Extraintestinal manifestations references
1. Navarro P, Gutiérrez-Ramírez L, Tejera-Muñoz A, Arias Á, Lucendo AJ. Systematic Review and Meta-Analysis: Prevalence of Non-Alcoholic Fatty Liver Disease and Liver Fibrosis in Patients with Inflammatory Bowel Disease. Nutrients. 2023;15(21):4507. Published 2023 Oct 24. doi:10.3390/nu15214507
2. Keetha Rao N, Ghodous S, Gurram A, et al. Prevalence and Associated Factors of Nonalcoholic Fatty Liver Disease in Patients with Inflammatory Bowel Disease: An Updated Global Systematic Review and Meta-Analysis of over 1.5 Million Individuals. Inflamm Bowel Dis. Published online October 17, 2025. doi:10.1093/ibd/izaf226
Treatment of Inflammatory Bowel Disease
Supportive care
5-Aminosalicylic acid (only for ulcerative colitis)
Biologic agents (anticytokine and anti-integrin medications) and small-molecule agents
Several classes of medications are helpful for IBD. Details of their selection and use are discussed under each disorder and in Medications for Inflammatory Bowel Disease.
Supportive care
Most patients and their families are interested in diet and stress management. The American Gastroenterological Association recommends that all patients with IBD follow a Mediterranean diet rich in fresh fruits and vegetables, monounsaturated fats, complex carbohydrates, and lean proteins, while limiting ultraprocessed foods, added sugar, and salt (1). Stress management may be helpful.
Treatment reference
1. Hashash JG, Elkins J, Lewis JD, Binion DG. AGA Clinical Practice Update on Diet and Nutritional Therapies in Patients With Inflammatory Bowel Disease: Expert Review. Gastroenterology. 2024;166(3):521-532. doi:10.1053/j.gastro.2023.11.303
Health Maintenance in Inflammatory Bowel Disease
Immunizations
Patients with IBD should receive the yearly influenza vaccination. Patients with IBD > 50 years old should receive pneumococcal vaccination. Pneumococcal immunization is also recommended in adult patients with IBD between 19 and 49 years of age who are receiving immune-modifying therapy and have had no prior pneumococcal vaccination. In all adults ≥ 50 years with IBD, vaccination against herpes zoster is also recommended. Those 19- to 49-year-olds receiving immune-modifying therapy should receive the recombinant herpes zoster vaccine. This vaccine should be given before starting immunosuppressive therapy when possible (1).
Routine vaccinations such as tetanus-diphtheria, hepatitis A, hepatitis B, and human papillomavirus should be given as per the Advisory Committee on Immunization Practices (ACIP) guidelines.
The American College of Gastroenterology (ACG) and the Canadian Association of Gastroenterology recommend that patients with IBD, including those on immunosuppressive therapy, receive an mRNA COVID-19 vaccine (1, 2).
Screening tests
All patients with inflammatory bowel disease should undergo surveillance for colorectal cancer beginning 8 years after symptom onset, regardless of their age. One exception is for patients with primary sclerosing cholangitis (PSC) who should begin annual surveillance immediately at the time of diagnosis, regardless of inflammatory bowel disease duration (3). Surveillance intervals are determined by risk stratification, generally with low-risk patients (no endoscopic or histologic evidence of active inflammation) undergoing colonoscopy every 2 to 5 years and high-risk patients requiring annual surveillance. High-risk patients include those with primary sclerosing cholangitis, active inflammation, family history of colorectal cancer diagnosed before age 50, colonic strictures, or prior dysplasia (4).
Female patients who are not receiving immunosuppressive therapy should be screened for cervical cancer every 3 years. Patients who are receiving immunosuppressive therapy should be screened for cervical cancer yearly within a year of the onset of sexual activity and, if younger than 30, should continue for 3 consecutive years of negative testing before increasing the screening interval to once every 3 years (1).
Patients with IBD should have annual screening for melanoma independent of the use of biologic therapy. All patients who are taking immunomodulating medications or biologic agents should be evaluated for nonmelanoma skin cancer annually.
Patients at risk of osteoporosis should have a dual-energy x-ray absorptiometry (DXA) scan.
Health maintenance references
1. Farraye FA, Melmed GY, Lichtenstein GR, et al. ACG Clinical Guideline Update: Preventive Care in Inflammatory Bowel Disease. Am J Gastroenterol. 2025;120(7):1447-1473. Published 2025 Jul 2. doi:10.14309/ajg.0000000000003541
2.Tse F, Moayyedi P, Waschke KA, et al. COVID-19 Vaccination in Patients With Inflammatory Bowel Disease: Communiqué From the Canadian Association of Gastroenterology. J Can Assoc Gastroenterol. 2021;4(1):49. Published 2021 Jan 27. doi:10.1093/jcag/gwaa046
3. National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines). Colorectal Cancer Screening, version 2.2025–June 24, 2025. https://www.nccn.org/professionals/physician_gls/pdf/colorectal_screening.pdf. Accessed February 2, 2025.
4. Rex DK, Anderson JC, Butterly LF, et al. Colorectal cancer screening: recommendations for physicians and patients from the U.S. Multi-Society Task Force on Colorectal Cancer. Gastrointest Endosc. 2024;100(3):352-381.
