Microscopic colitis is a type of inflammatory bowel condition where the colon looks completely normal during a colonoscopy but shows clear signs of inflammation under a microscope. It causes chronic, watery diarrhea, typically five to ten times per day, and affects roughly 4 to 9 people per 100,000 each year. Unlike ulcerative colitis or Crohn’s disease, the inflammation is only visible in tissue samples, which is how it gets its name.
Two Subtypes With Different Markers
Microscopic colitis comes in two forms: collagenous colitis and lymphocytic colitis. Both cause the same symptoms, but they look different under a microscope. In collagenous colitis, a thick band of collagen protein builds up beneath the surface layer of the colon wall. Normally this layer is thin, but in collagenous colitis it measures more than 10 micrometers, sometimes several times thicker than normal. In lymphocytic colitis, the hallmark is an excess of immune cells (lymphocytes) embedded within the lining of the colon, at least 20 per 100 surface cells.
Lymphocytic colitis is slightly more common, with a pooled incidence of about 4.85 per 100,000 people per year compared to 4.14 for collagenous colitis. The distinction between the two subtypes matters mainly for diagnosis. Treatment is the same regardless of which type you have, and neither form carries a higher risk of progressing to a more serious condition.
Who Gets It
Microscopic colitis overwhelmingly affects women and people over 50. In a large study of over 1,200 cases, the average age at diagnosis was 63, and about 73% of patients were female. The gender gap is especially pronounced in collagenous colitis, where women are diagnosed about three times as often as men. For lymphocytic colitis, the ratio is closer to two to one.
Nearly 39% of people with microscopic colitis also have another autoimmune condition, such as celiac disease, thyroid disorders, or rheumatoid arthritis. That rate is roughly double what’s seen in people with other types of inflammatory bowel disease. If you already have one autoimmune condition and develop persistent watery diarrhea, microscopic colitis is worth considering.
Symptoms and What They Feel Like
The defining symptom is watery, non-bloody diarrhea. Most people experience five to ten loose bowel movements a day, though some have fewer. The diarrhea often comes on gradually over weeks or months rather than hitting all at once, which is part of why many people wait a long time before seeking help. Unlike inflammatory bowel disease, there’s no visible blood in the stool.
Other common symptoms include abdominal cramping, bloating, fatigue, and unintentional weight loss. Some people also experience urgency or fecal incontinence, which can significantly affect daily life. Nighttime diarrhea is possible and can disrupt sleep. These symptoms tend to wax and wane. Some people have stretches of weeks or months where symptoms improve, only for them to return.
Medications That Can Trigger It
Certain common medications are strongly linked to the development of microscopic colitis. Proton pump inhibitors (the acid-blocking drugs many people take for heartburn) carry the strongest individual association, roughly tripling the risk. Anti-inflammatory painkillers like ibuprofen and naproxen nearly double the risk, and certain antidepressants in the SSRI class roughly double it as well.
The most dangerous combination appears to be taking a proton pump inhibitor and an anti-inflammatory painkiller at the same time, which raises the risk about fivefold. The risk increases further with prolonged use over 4 to 12 months. Statins, despite being widely used, do not appear to increase the risk. If you develop chronic watery diarrhea while taking any of these medications, your doctor may consider whether the drug could be playing a role.
How It’s Diagnosed
Because the colon looks normal during a standard colonoscopy, diagnosis requires taking small tissue samples (biopsies) from multiple spots along the colon and examining them under a microscope. This is the only way to confirm microscopic colitis. Many people go through the process expecting the colonoscopy itself to reveal something, and it’s the biopsy results that provide the answer.
If the pathologist finds a thickened collagen band greater than 10 micrometers, it’s collagenous colitis. If they find elevated lymphocyte counts without that collagen thickening, it’s lymphocytic colitis. There’s also an “incomplete” form where the collagen band is thicker than normal (between 5 and 10 micrometers) but doesn’t fully meet the diagnostic threshold. This is sometimes treated the same way if symptoms are significant.
Treatment and What to Expect
The first step is reviewing any medications that might be contributing. Stopping or switching a proton pump inhibitor, anti-inflammatory painkiller, or SSRI sometimes resolves symptoms entirely.
When that’s not enough, the standard first-line treatment is budesonide, a locally acting steroid that targets the gut with fewer body-wide side effects than traditional steroids. The typical starting approach is 9 mg per day for eight weeks. Most people respond well, with diarrhea improving significantly within the first couple of weeks.
The challenge with microscopic colitis is relapse. Many people find that symptoms return after stopping treatment. If that happens, budesonide can be continued at a lower dose, usually 6 mg per day or less, for six to twelve months. Some people need long-term low-dose treatment to keep symptoms under control. For the minority who don’t respond to budesonide, other immune-modifying treatments are available, though they’re rarely needed.
Diet and Lifestyle Factors
Despite what you might expect, large studies have not identified specific dietary components that increase the risk of developing microscopic colitis. A study following a large cohort over an extended period found no association between protein, carbohydrate, fat, fiber, or sugar intake and the condition. There isn’t strong evidence that any particular food causes it.
That said, many people with active symptoms find that caffeine, dairy, and high-fat foods make their diarrhea worse in the short term. Reducing these during flares is a reasonable approach, even if they didn’t cause the condition. Staying hydrated is important given the volume of fluid lost through frequent watery stools.
Long-Term Outlook
Microscopic colitis is a chronic condition, but it carries a reassuring long-term prognosis. It does not increase your risk of colorectal cancer. In fact, a meta-analysis covering over 50,000 patients found that people with microscopic colitis actually had a lower rate of both colorectal cancer and precancerous polyps compared to the general population. Because of this, professional guidelines do not recommend any extra colonoscopy surveillance specifically for microscopic colitis.
Most people achieve good symptom control with medication, and some eventually go into remission without ongoing treatment. The condition does not damage the colon in a progressive way like Crohn’s disease or ulcerative colitis can, and it doesn’t lead to surgery. For many people, the biggest challenge is the time it takes to get diagnosed, since the symptoms overlap with irritable bowel syndrome and other common gut conditions, and the colon looks normal on visual inspection.