Microscopic colitis is a form of inflammatory bowel disease (IBD) that affects the colon and rectum (large bowel). There are two different forms of the condition — collagenous colitis and lymphocytic colitis — that share similar symptoms. The main difference is that in collagenous colitis, the colon's lining contains more collagen than usual and in lymphocytic colitis, there are more white blood cells (lymphocytes) in the colon's lining than usual. MORE: Understanding the etiology of inflammatory bowel disease According to Crohn's and Colitis UK, it's called microscopic colitis because the inflammation is only visible when the affected tissue is studied under a microscope, unlike two similar conditions, ulcerative colitis and Crohn's disease. The main symptom of both types of microscopic colitis is very watery diarrhea which can quickly lead to dehydration. Diarrhea may begin without warning and is often chronic. Other symptoms include abdominal pain, weight loss, incontinence, fatigue, excess wind, bloating, and muscle and joint pain. Microscopic colitis tends to affect older people, typically striking between the ages of 50 and 60. Lymphocytic colitis affects men and women equally, whereas collagenous colitis is more prevalent in women. The exact cause of the condition is unknown but it's suspected that it's an autoimmune disease like other forms of IBD. Scientists have studied various links to the disease including smoking, the use of certain over-the-counter and prescription medications, infections and a reaction to gut bacteria. There is no cure for microscopic colitis, but there are treatments that can help ease the symptoms of the disease including diet, over-the-counter diarrhea medications, steroids, and anti-inflammatory drugs.