Microscopic colitis is swelling and irritation, called inflammation, of the large intestine. This large intestine is also called the colon. Microscopic colitis causes symptoms of watery diarrhea.

The condition gets its name from needing to look at colon tissue under a microscope to diagnose it. The tissue appears typical on exam with a colonoscopy or flexible sigmoidoscopy.

There are two subtypes of microscopic colitis:

  • Collagenous colitis, in which a thick layer of protein called collagen grows in colon tissue.
  • Lymphocytic colitis, in which white blood cells called lymphocytes increase in colon tissue.

Researchers believe collagenous (kuh-LAYJ-uh-nus) colitis and lymphocytic colitis may be forms of the same condition. Symptoms, testing and treatment are the same for both subtypes.


Symptoms of microscopic colitis include:

  • Watery diarrhea.
  • Belly pain, cramps or bloating.
  • Weight loss.
  • Nausea.
  • Not being able to control bowel movements, called fecal incontinence.
  • The body not having enough water, called dehydration.

The symptoms of microscopic colitis can come and go. At times, symptoms improve on their own.

When to see a doctor

If you have watery diarrhea that lasts more than a few days, contact your healthcare professional to diagnose and treat your condition.


It's not clear what causes the swelling and irritation, called inflammation, of the colon found in microscopic colitis. Researchers believe that the causes may include:

  • Medicines that can inflame the lining of the colon.
  • Bile acid not absorbed as it should be that inflames the lining of the colon.
  • Bacteria that make toxins or viruses that interact with the lining of the colon.
  • Autoimmune disease linked to microscopic colitis, such as rheumatoid arthritis, celiac disease or psoriasis. Autoimmune disease happens when the body's immune system attacks healthy tissues.

Risk factors

Risk factors for microscopic colitis include:

  • Age. Microscopic colitis is most common in people older than age 50.
  • Sex. Women are more likely to have microscopic colitis than are men. Some studies suggest a link between post-menopausal hormone therapy and microscopic colitis.
  • Autoimmune disease. People with microscopic colitis sometimes also have an autoimmune disorder, such as celiac disease, thyroid disease, rheumatoid arthritis, type 1 diabetes or psoriasis.
  • Genetic link. Research suggests that there may be a link between microscopic colitis and a family history of irritable bowel syndrome.
  • Smoking. Recent research studies have shown a link between tobacco smoking and microscopic colitis, mostly in people ages 16 to 44.

Some research studies show a link between using certain medicines that may increase the risk of microscopic colitis. But not all studies agree.

Medicines that may be linked to the condition include:

  • Pain relievers, such as aspirin, ibuprofen (Advil, Motrin IB, others) and naproxen sodium (Aleve).
  • Proton pump inhibitors including lansoprazole (Prevacid), esomeprazole (Nexium), pantoprazole (Protonix), rabeprazole (Aciphex), omeprazole (Prilosec) and dexlansoprazole (Dexilant).
  • Selective serotonin reuptake inhibitors (SSRIs) such as sertraline (Zoloft).
  • Acarbose.
  • Flutamide.
  • Ranitidine.
  • Carbamazepine (Carbatrol, Tegretol, others).
  • Clozapine (Clozaril, Versacloz).
  • Entacapone (Comtan).
  • Paroxetine (Paxil).
  • Simvastatin (Flolipid, Zocor).
  • Topiramate (Topamax, Qsymia, others).


There are minimal complications for most people once microscopic colitis is successfully treated. The condition does not increase the risk of colon cancer.