The exact cause of Crohns disease is unknown. Researchers believe the following factors may play a role in causing Crohns disease: - autoimmune reaction - genes - environment Autoimmune reaction. Scientists believe one cause of Crohns disease may be an autoimmune reactionwhen a persons immune system attacks healthy cells in the body by mistake. Normally, the immune system protects the body from infection by identifying and destroying bacteria, viruses, and other potentially harmful foreign substances. Researchers believe bacteria or viruses can mistakenly trigger the immune system to attack the inner lining of the intestines. This immune system response causes the inflammation, leading to symptoms. Genes. Crohns disease sometimes runs in families. Research has shown that people who have a parent or sibling with Crohns disease may be more likely to develop the disease. Researchers continue to study the link between genes and Crohns disease. Environment. Some studies suggest that certain things in the environment may increase the chance of a person getting Crohns disease, although the overall chance is low. Nonsteroidal anti-inflammatory drugs,1 antibiotics,2 and oral contraceptives2 may slightly increase the chance of developing Crohns disease. A high-fat diet may also slightly increase the chance of getting Crohns disease. 3 Some people incorrectly believe that eating certain foods, stress, or emotional distress can cause Crohns disease. Emotional distress and eating certain foods do not cause Crohns disease. Sometimes the stress of living with Crohns disease can make symptoms worse. Also, some people may find that certain foods can trigger or worsen their symptoms. 
What causes Crohns Disease ?