Mucus is a normal part of stool. Your colon is lined with a gel-like mucus layer, made by goblet cells in the bowel lining, that protects the wall and keeps gut bacteria at a distance. The inner layer is renewed about every hour.[1] So seeing some mucus in or on your stool isn't automatically a sign of disease, and in IBS it's a familiar symptom.
Why does IBS cause mucus in stool?
Mucus has been linked with IBS since the first diagnostic criteria. In the 1978 study behind the Manning criteria, passing mucus was common among people later confirmed to have IBS.[2] The Rome III criteria listed passage of mucus among the symptoms that support an IBS diagnosis,[3] and UK NICE guidance still counts it as one of four supporting symptoms, alongside altered stool passage, bloating and symptoms made worse by eating.[4] The current Rome IV criteria are built around pain and bowel habit and don't use mucus to make the diagnosis.[5]
Why some people with IBS pass more visible mucus than others isn't well understood. What matters in practice is that mucus on its own, without blood or other warning signs, fits with IBS.
Does mucus in stool mean you have IBS?
Not by itself. A systematic review of how well individual symptoms identify IBS found that passing mucus did very little to separate IBS from other causes of lower-gut symptoms. Its likelihood ratio of 1.2 is barely better than chance.[6] IBS is diagnosed from recurrent belly pain linked to bowel movements or changes in stool. Mucus can add support, but it isn't the deciding feature.[4][5]
If you haven't been diagnosed, see a doctor rather than self-diagnosing. Read do I have IBS? and how IBS differs from IBD.
When should you see a doctor about mucus in stool?
| What you notice | What to do |
|---|---|
| Mucus with your usual IBS symptoms, no warning signs | Usually fits IBS.[4] Mention it at your next visit if it changes. |
| Mucus or pus with blood, or rectal bleeding | See a doctor. These are common symptoms of ulcerative colitis, a form of inflammatory bowel disease.[7] |
| Mucus with an urgent need to go and ongoing diarrhea | Urgency and diarrhea are also common in ulcerative colitis.[7] See a doctor right away if diarrhea lasts more than 2 days or you have six or more loose stools a day.[8] |
| Mucus with high fever, severe belly or rectal pain, or signs of dehydration | See a doctor right away. US health guidance lists these among the signs that need prompt care.[8] |
| Black, tarry stools, or stools with red blood or pus | See a doctor right away.[8] |
| Weight loss you can't explain, anemia, symptoms that wake you at night, or onset after 50 | These are IBS alarm features and need investigating.[9] |
For a full list of warning signs, see IBS red flags.
What will a doctor check?
Your doctor will ask about your symptoms, how long you've had them and what your stools look like, and examine you. For suspected IBS with diarrhea, the American College of Gastroenterology suggests a celiac blood test and a fecal calprotectin test, a stool marker of bowel inflammation used to help rule out inflammatory bowel disease.[10] UK NICE guidance recommends a blood count, inflammation markers and celiac antibody tests for people who meet the IBS criteria.[4]
What should you track?
Note when you see mucus, how much, and whether it comes with blood, pain, urgency or a change in stool type on the Bristol Stool Form Scale. A record over a few weeks shows whether mucus is part of your usual pattern or something new. IBS Clue, an iPhone app coming soon, includes a Bristol stool log and can export a PDF report to bring to your appointment.