No one knows exactly what causes ulcerative colitis, an inflammatory bowel disease that can cause diarrhea, abdominal pain, dehydration and malnutrition. Scientists and physicians believe ulcerative colitis may be an autoimmune condition, but they continue to study the disease, hoping to discover more about its underlying causes and contributing factors. Learn more about current research into ulcerative colitis causes, including heritable and environmental factors that could trigger the immune system. Immune System Malfunction The immune system is designed to protect the body from invaders such as bacteria and viruses that can cause infection and disease. Occasionally, though, the immune system will attack the body itself. In ulcerative colitis, the immune system seems to attack the lining of the large intestine, creating ulcers and inflammation and disrupting normal digestion. Scientists are still trying to figure out what causes the immune system to target what appears to be an otherwise healthy part of the body. They suspect antigens on bacteria and viruses might falsely trigger the ulcerative colitis attack when the immune system discovers chemically similar molecules on gut cell. But so far, they have not been able to identify any specific bacteria or viruses that cause the immune system to target the lining of the colon. As researchers learn more about the immune system and the gut microbiome (the collection of microscopic organisms that inhabit the digestive system), they may uncover additional information that will help them understand the development and progression of ulcerative colitis. Abnormal Genes Healthcare providers and patients have noticed ulcerative colitis tends to run in families, so they suspect the disease might be hereditary. Scientists know the disease is most common in white people of European origin, particularly people of Ashkenazi Jewish descent. (People from Ashkenazi Jewish families have approximately a 4.5% lifetime risk of developing ulcerative colitis, compared to a 1.6% lifetime risk for non-Jewish white people.) These findings strongly suggest abnormal genes, which can be passed down from generation to generation, may be a cause of ulcerative colitis. However, scientists have not yet been able to identify specific genes or genetic mutations linked to the development of ulcerative colitis. And while 20% of people with ulcerative colitis have a close family member with the disease, the remaining 80% do not. This means abnormal genes and heredity cannot be the only causes of ulcerative colitis. Environment Many diseases are caused by a combination of factors. For instance, scientists know certain gene mutations increase a woman’s risk of developing breast cancer. But breast cancer does not develop in all women who have those genetic mutations, so scientists suspect other factors, including environmental exposures, overall health, and reproductive history, also play a role in the development of the disease. Researchers suspect ulcerative colitis may be the same. Scientists know a high-fat diet may increase the risk of developing ulcerative colitis. Regular intake of non-steroidal anti-inflammatory drugs (such as aspirin), oral contraceptives, and antibiotics is also associated with an increased risk. Researchers are trying to figure out how these exposures trigger or influence the development of disease. Years ago, people believed stress could cause ulcerative colitis. Some people do experience symptom flare-ups during periods of high stress, but doctors do not believe emotional distress can cause ulcerative colitis. Patients and healthcare providers hope continuing research into the causes of ulcerative colitis will eventually point the way toward more effective and more efficient treatments.