Ulcerative colitis is a chronic inflammatory disease that affects the lining of the large intestine (colon) and rectum. People with this condition have tiny ulcers and small abscesses in their colon and rectum that flare up periodically and cause bloody stools and diarrhea.

Crosscut of colon with diverticula.

Crosscut of colon and rectum with ulcerative colitis.

Ulcerative colitis is characterized by alternating periods of flare-ups and remission in which the disease appears to have disappeared. The periods of remission can last from weeks to years.

The inflammation usually begins in the rectum and then spreads to other segments of the colon. How much of the colon is affected varies from person to person. If the inflammation is limited to the rectum, the disease may be called ulcerative proctitis. Ulcerative colitis, unlike Crohn's disease, does not affect the esophagus, stomach or small intestine.

When grouped together, ulcerative colitis and Crohn's disease are referred to as inflammatory bowel disease because they cause inflammation of the bowel.

Who gets ulcerative colitis?

Ulcerative colitis can be inherited. Up to 25% of people with inflammatory bowel disease have a first-degree relative (mother, father, brother, sister) with the disease.

What are the symptoms of ulcerative colitis?

The main symptom of ulcerative colitis is diarrhea that often becomes bloody. Occasionally, the symptoms of ulcerative colitis include severe bloody diarrhea, dehydration, abdominal pain, and fever. Other symptoms may include painful, urgent bowel movements or pus or blood in the stool. Ulcerative colitis may be associated with weight loss, joint pain, anemia (a deficiency in red blood cells), or skin lesions (sores).

What causes ulcerative colitis?

The cause of ulcerative colitis remains unknown, but it is likely caused by an abnormal response of the immune system in the gastrointestinal tract to something in the gut -- food or bacteria in the intestines, or even the lining of the bowel -- that causes uncontrolled inflammation.