Reviewed by: HU Medical Review Board | Last Reviewed: January 2018.

Inflammation is a key feature of inflammatory bowel disease (IBD). The two main forms of IBD are Crohn’s disease and ulcerative colitis.1 In Crohn's disease, inflammation can affect any part of the digestive tract, from the mouth to the rectum, and is most often found at the end of the small intestine (ileum).2,In ulcerative colitis, inflammation occurs in the large intestine.1

Inflammation develops when the immune system fights something that is harmful—or that seems to be harmful.4 The body releases chemicals that cause blood vessels to widen. This brings more blood to the damaged area. The area becomes red and swollen. White blood cells travel to the affected areas to fight invading bacteria or viruses (microorganisms).

Why does inflammation develop in inflammatory bowel disease?

Inflammation is helpful after an injury or infection. However, the immune system sometimes overreacts to something harmless. Scientists think that the inflammation in IBD happens when your immune system overreacts to harmless microorganisms in your digestive tract.5,6 The white blood cells gather in the intestine to fight the microorganisms. They remain in the intestine, causing lasting inflammation. This chronic inflammation causes damage to the digestive tract.1

People with IBD may also have inflammation in other parts of the body. The joints, skin, and eyes and liver are particularly likely to be affected.7,8

What other conditions can cause inflammation in the digestive tract?

Crohn’s disease and ulcerative colitis are the two main forms of IBD. Several other less common diseases also cause inflammation in the digestive tract. These include:

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  • Collagenous colitis
  • Lymphocytic colitis
  • Diversion colitis
  • Behçet's disease

How is inflammation in the digestive tract evaluated?

If you have symptoms of IBD, your health care provider will do some laboratory tests. Some of these blood tests check for inflammation, including white blood cell counts, blood sedimentation rates, and C-reactive protein.9 Your provider may also test a sample of stool for markers of inflammation.

Your provider will confirm the diagnosis by looking inside your digestive tract for signs of IBD and taking samples of tissue.9 The procedure to do this is called colonoscopy with biopsy. Your doctor performs this procedure using a long, thin tube with a very small camera and light. The camera lets your doctor see inside your digestive tract.

Tissue samples are taken from the digestive tract. A doctor will look at the samples with a microscope for signs inflammation. About 30% to 45% of people with Crohn’s disease have granulomas.10,11 Granulomas form when inflammatory cells collect in one spot.12 Granulomas are not present in ulcerative colitis, and their presence is one way doctors can differentiate between the two diseases.13

What medications treat inflammation related to IBD?

The medications used to treat IBD reduce inflammation. They work in a variety of ways.

Aminosalicylates are used to treat ulcerative colitis and mild to moderate IBD.14,15 These medications block a chemical called prostaglandin from forming.14 This reduces pain and inflammation. Aminosalicylates treat local inflammation in the digestive tract, rather than throughout the whole body. These medications come in many forms. The tablet forms have a special coating that only dissolves once the medication has reached its target in the digestive tract.15 These medications also come as an enema or suppository. These forms treat inflammation in the lower part of the large intestine. An enema involves injecting a liquid medication into the large intestine via the rectum. A suppository is a solid medication that is inserted into the rectum, where it dissolves.

Corticosteroids are used for the short-term treatment of Crohn’s disease and ulcerative colitis. They reduce inflammation and suppress the immune system. Several corticosteroids reduce inflammation throughout the whole body. One corticosteroid, budesonide, mainly works in the digestive tract. This approach causes fewer side effects.15

Immunomodulators weaken the immune system. This reduces the inflammatory response.15 These medications are used as a long-term treatment for IBD.15

Biologics are medications for treating moderate to severe IBD that hasn't responded to other treatment.15 Inflammation is a complicated process with many steps. At each step, certain things must happen in order for the process to continue. Biologic medications target specific proteins with a role in this process. By blocking one step, they can prevent the whole process from continuing.

What are complications of long-term inflammation?

Inflammation eventually causes scarring in your intestine. Scar tissue builds up over time, making it harder for food and waste to pass through the digestive tract. The narrowing of the digestive tract is called a stricture.16

Large, inflamed masses can form in the abdomen.12 Theses masses are called abscesses. Abscesses are more common in Crohn's disease than ulcerative colitis. About 10% to 30% of people with Crohn’s disease will have an abscess.17 Abscesses are experienced by about 20% of people with ulcerative colitis.16 One cause of abscess formation is inflammation that extends deep into wall of the intestine.

Abscesses can cause abnormal connections to form between the intestine and other organs.17 These connections are called fistulas. Fistulas can develop between different loops of the intestine. They also develop between the intestine and other structures, such as the bladder or skin. Fistulas also can cause abscesses to form. Fistulas are more common in Crohn's disease than ulcerative colitis, although they can occur with either disease.16