Crohn's disease is a type of inflammatory bowel disease (IBD) that can affect any part of the entire digestive tract. It causes inflammation and in severe cases, ulcers can form. Symptoms often include abdominal pain, diarrhea, fever, abdominal distension, and weight loss.
The cause of Crohn's disease is unknown. Researchers think that an autoimmune reaction may be one cause. An autoimmune reaction happens when your immune system attacks healthy cells in your body. Genetics may also play a role, since Crohn's disease can run in families.
Stress and eating certain foods don't cause the disease, but they can make your symptoms worse.
Source : MedlinePlus. US National Library of Medicine.
As well as genetics, faulty immune system balance, microbial infections, and environmental factors are also under investigation as possible contributing factors. See: Wikipedia
Also see :Ulcerative colitisplugin-autotooltip__plain plugin-autotooltip_bigUlcerative colitis
"Ulcerative colitis (UC) is a long-term condition that results in inflammation and ulcers of the colon and rectum. The primary symptoms of active disease are abdominal pain and diarrhoea mixed with blood. Weight loss, fever, and anaemia may also occur. and Irritable bowel syndrome (IBS)plugin-autotooltip__plain plugin-autotooltip_bigIrritable bowel syndrome (IBS)
"The most common condition seen in gastrointestinal outpatient clinics is irritable bowel syndrome (IBS), which has a prevalence rate of 14-24% in women and 5-19% in men. [...] There is no known structural or anatomical explanation that accounts for the pathophysiology, and the exact cause remains unknown"