The National Ulcerative Colitis Alliance (NUCA) is a qualified 501(c)(3) tax-exempt organization.

What Causes Ulcerative Colitis?

The exact cause of ulcerative colitis (UC) is unknown. Researchers believe the following factors may play a role in causing UC:

  • Overactive intestinal immune system
  • Genes
  • Environment

Overactive Intestinal Immune System

One cause of UC may be an abnormal immune reaction in the intestine. Normally, the immune system protects the body from infection by identifying and destroying bacteria, viruses, and other potentially harmful foreign substances. Bacteria or viruses may mistakenly trigger the immune system to attack the inner lining of the large intestine. This immune system response causes inflammation, leading to symptoms.


Ulcerative colitis sometimes runs in families. Studies have shown that certain abnormal genes may appear in people with UC. However, researchers have not been able to show a clear link between the abnormal genes and UC.


Some studies suggest that certain things in the environment may increase the chance of a person developing UC, although the overall chance is low. Nonsteroidal anti-inflammatory drugs, antibiotics, and oral contraceptives may slightly increase the chance of developing UC. A high-fat diet may also slightly increase the chance of developing UC.

Some people believe eating certain foods, stress, or emotional distress can cause UC. Emotional distress does not seem to cause UC; however, a few studies suggest that stress may increase a person's chance of having a flare-up of UC. Also, some people may find that certain foods can trigger or worsen symptoms.


The National Institute of Diabetes and Digestive and Kidney Diseases. Ulcerative colitis. Accessed February 14, 2018.