Ulcerative colitis (Colitis ulcerosa, UC) is a form of inflammatory bowel disease (IBD) that causes inflammation and ulcers in the colon. The disease is a type of colitis, which is a group of diseases that cause inflammation of the colon, the largest section of the large intestine, either in segments or completely. The main symptom of active disease is usually constant diarrhea mixed with blood, of gradual onset. IBD (Crohn's disease (CD) and ulcerative colitis (UC)) is often confused with irritable bowel syndrome (IBS).Ulcerative colitis has much in common with Crohn's disease, another form of IBD, but what sets it apart from Crohn's disease is that ulcerative colitis, as its name suggests, only affects the colon and rectum, leaving the rest of the gastrointestinal tract unscathed, while Crohn's disease can affect the whole GI tract from mouth to anus. Also, surgical removal of the colon and rectum cures ulcerative colitis, which actually means the disease does not recur after surgery, unlike Crohn's disease, which has a tendency to recur after surgery to remove the abnormal part of the bowel and connect the healthy ends. Ulcerative colitis is an intermittent disease, with periods of exacerbated symptoms, and periods that are relatively symptom-free. Although the symptoms of ulcerative colitis can sometimes diminish on their own, the disease usually requires treatment to go into remission. Ulcerative colitis has an incidence of 1 to 20 cases per 100,000 individuals per year, and a prevalence of 8 to 246 per 100,000 individuals.The disease is more prevalent in northern countries of the world, as well as in northern areas of individual countries or other regions. Rates tend to be higher in more affluent countries, which may indicate the increased prevalence is due to increased rates of diagnosis. It may also indicate that an industrial or Western diet and lifestyle increases the prevalence of this disease, including symptoms which may or may not be related to ulcerative colitis. Although UC has no known cause, there is a presumed genetic component to susceptibility. The disease may be triggered in a susceptible person by environmental factors. Dietary modification may reduce the discomfort of a person with the disease.Like Crohn's disease, ulcerative colitis is both classed as and managed as an autoimmune disease. Management is with anti-inflammatory drugs, immunosuppression, and biological therapy targeting specific components of the immune response. Colectomy (partial or total removal of the large bowel through surgery) is occasionally necessary if the disease is severe, does not respond to treatment, or if significant complications develop. A total proctocolectomy (removal of the entirety of the large bowel and rectum) can cure ulcerative colitis as the disease only affects the large bowel and rectum and does not recur after removal of the latter. While extra-intestinal symptoms will remain, complications may develop.