Colitis is a broad term that refers to inflammation in the colon—which is the biggest part of the largest intestine. Colitis is not a disease in and of itself, but is rather a sign of a condition. There are a variety of causes of colitis, including infection, inflammatory bowel disease (IBD), microscopic colitis, ischemic colitis, and allergic colitis (a condition found in infants). aldomurillo / Getty Images Common Causes Inflammatory Bowel Disease The various forms of IBD, which include Crohn's disease, ulcerative colitis, and indeterminate colitis, can all lead to the development of colitis. The causes of IBD are not understood, but theories do exist. These diseases are called "idiopathic," meaning that it's not yet clear what the underlying series of changes in the body are that lead to the development of the disease. However, some clues are being investigated to learn more about ca