Crohn's disease is a type of inflammatory bowel disease (IBD) that may affect any part of the gastrointestinal tract from mouth to anus. Signs and symptoms often include abdominal pain, diarrhea (which may be bloody if inflammation is severe), fever, and weight loss. Other complications may occur outside the gastrointestinal tract and include anemia, skin rashes, arthritis, inflammation of the eye, and tiredness. The skin rashes may be due to infections as well as pyoderma gangrenosum or erythema nodosum. Bowel obstruction may occur as a complication of chronic inflammation, and those with the disease are at greater risk of bowel cancer.While the cause of Crohn's disease is unknown, it is believed to be due to a combination of environmental, immune, and bacterial factors in genetically susceptible individuals. It results in a chronic inflammatory disorder, in which the body's immune system attacks the gastrointestinal tract, possibly targeting microbial antigens. While Crohn's is an immune-related disease, it does not appear to be an autoimmune disease (in that the immune system is not being triggered by the body itself). The exact underlying immune problem is not clear; however, it may be an immunodeficiency state. About half of the overall risk is related to genetics with more than 70 genes having been found to be involved. Tobacco smokers are twice as likely to develop Crohn's disease as nonsmokers. It also often begins after gastroenteritis. Diagnosis is based on a number of findings including biopsy and appearance of the bowel wall, medical imaging and description of the disease. Other conditions that can present similarly include irritable bowel syndrome and Behçet's disease.There are no medications or surgical procedures that can cure Crohn's disease. Treatment options are intended to help with symptoms, maintain remission, and prevent relapse. In those newly diagnosed, a corticosteroid may be used for a brief period of time to rapidly improve symptoms alongside another medication such as either methotrexate or a thiopurine used to prevent recurrence. Stopping smoking is recommended in people with Crohn's disease. One in five people with the disease is admitted to hospital each year, and half of those with the disease will require surgery for the disease at some point over a ten-year period. While surgery should be used as little as possible, it is necessary to address some abscesses, certain bowel obstructions, and cancers. Checking for bowel cancer via colonoscopy is recommended every few years, starting eight years after the disease has begun.Crohn's disease affects about 3.2 per 1,000 people in Europe and North America. It is less common in Asia and Africa. It has historically been more common in the developed world. Rates have, however, been increasing, particularly in the developing world, since the 1970s. Inflammatory bowel disease resulted in 47,400 deaths in 2015 and those with Crohn's disease have a slightly reduced life expectancy. It tends to start in the teens and twenties, although it can occur at any age. Males and females are equally affected. The disease was named after gastroenterologist Burrill Bernard Crohn, who, in 1932, together with two other colleagues at Mount Sinai Hospital in New York, described a series of patients with inflammation of the terminal ileum of the small intestine, the area most commonly affected by the illness.