What Causes Ulcerative Colitis?

Ulcerative colitis happens when your body’s immune system doesn’t work properly. It causes inflammation in the inner lining of your colon. The irritation and swelling in turn lead to ulcers and open sores in the lining.

Your immune system defends you from infections, illnesses, and things that don’t belong in your body. But in an autoimmune disease like ulcerative colitis, it mistakenly attacks your own body.

It sends in your white blood cells, which attack your intestinal lining. That leads to ongoing inflammation.

No one knows exactly what causes ulcerative colitis. But experts think that one of three things may trigger it.


You might have inherited a gene that causes ulcerative colitis. It could run in your family. Experts have found certain abnormal genes in some people who have it.

Immune System

An infection might have triggered your immune system, but then for some reason, it doesn’t turn off. That leads to the colon inflammation that causes symptoms of ulcerative colitis.


A germ, like a virus in your environment, might raise your chances of developing ulcerative colitis.

If you use nonsteroidal anti-inflammatory drugs, antibiotics, or birth control pills, your chances to develop it may increase slightly. It’s possible a high-fat diet is related to it, too.

A few other things could be related to the cause or might trigger a flare-up:

  • Stress
  • Emotional distress
  • Some kinds of food

Who’s At Risk?

Anyone can get ulcerative colitis. But if you’re an older man, you’re more likely to get it than an older woman. And even though it can strike at any age, it usually begins before you’re 30 or after 60.

If someone in your family has ulcerative colitis, you’re more likely to get it, too. But only 20% of people with the disease also have a close relative with it.

If you’re white and of European descent or if you’re Jewish, you’re also more likely to get the condition.

WebMD Medical Reference Reviewed by Sabrina Felson, MD on November 07, 2020



Peyrin-Biroulet, L. Digestive and Liver Disease, published online May 3, 2016.

Mayo Clinic: “Ulcerative colitis.”

Crohn’s & Colitis Association of America: “Colitis Treatment Options.”

National Institute of Diabetes and Digestive and Kidney Diseases: “Ulcerative Colitis.” 

Chumanevich, A. Oncotarget, published online July 14, 2016.

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