What is inflammatory bowel disease (IBD)?

IBD is the name of a group of diseases in which the small intestine and the large intestine (the bowels) become red and swollen. IBD is not the same as irritable bowel syndrome (IBS). Unlike IBD, IBS does not involve inflammation or permanent damage in the gastrointestinal (GI) tract.

The most common forms of IBD are Crohn's disease and ulcerative colitis.

Crohn’s disease

Crohn’s disease can affect any part of the GI tract, from the mouth to the anus. Crohn’s disease causes inflammation that may affect all the layers of the bowel wall.

Experts are not sure what causes Crohn’s disease, but diet and stress seem to make the condition worse. In people with Crohn’s disease, the body’s immune system “thinks” that some harmless bacteria and other substances in the GI tract are damaging to the body. The immune system attacks and destroys the bacteria. This causes chronic (long-lasting) inflammation. Over time, this can cause a hole in the lining of the bowels.

Crohn’s disease often runs in families: people who have close relatives with the condition are more likely to have Crohn’s disease themselves. Males and females of any age can get Crohn’s disease, but it is most common in people aged 15 to 35 years.

Ulcerative colitis

Ulcerative colitis affects the large intestine (colon) and the rectum. It causes sores and inflammation. Ulcerative colitis usually begins in the rectum and the lower colon. Over time, it may spread to the entire colon.

Experts are not sure what causes ulcerative colitis, but the following factors seem to be related to the condition:

  • Genes. Ulcerative colitis tends to run in families
  • The immune system’s reaction to substances in the body. In people with ulcerative colitis, the body’s immune system “thinks” that some harmless bacteria and other substances in the colon are harmful. The immune system attacks and destroys those substances. This causes chronic (long-lasting) inflammation
  • The immune system’s reaction to infection. Inflammation is a healthy response to infections caused by bacteria or viruses. In most people, the inflammation goes away when the infection goes away. But in people with ulcerative colitis, the inflammation doesn’t stop. This leads to symptoms of ulcerative colitis

Men and women of any age can have ulcerative colitis, but most people are in their mid-30s when they find out they have the condition.