What Can Cause Mucus in the Stool?

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Mucus is a stringy, clear, white or yellow substance that is typically found in a healthy stool. Mucus in the stool may be considered a common symptom of certain digestive conditions, such as irritable bowel syndrome (IBS) and ulcerative colitis (one form of inflammatory bowel disease, or IBD). Other conditions that can cause visible mucus in the stool include bacterial infections, anal fissures, a bowel obstruction, or Crohn's disease (the second main form of IBD).

While it is normally present in small amounts, mucus in the stool that can be seen with the naked eye could be a sign that something in the digestive system is changing. Although it may seem gross and cause worry, it's important to understand the reasons for the changes in order to better address them.

Overview

Mucus is a clear, white, or yellow substance with a consistency of jelly. It is produced by the mucus membrane of the large intestine. Mucus is also produced by other organs in the body, such as the lungs, where it helps to trap any foreign particles that are inhaled.

In the intestines, mucus protects the inner lining and because it is slippery, it helps ease along the passage of stool. Passing mucus in the stool is not harmful in and of itself, because it is a normal part of stool, but too much could also be a sign of a disease or condition that may require treatment. If the mucus layer is shedding too much, it could make the colon more susceptible to bacteria.

Causes

Ulcerative Colitis. In ulcerative colitis, the mucus membrane of the large intestine (colon) becomes inflamed and develops small sores that are called ulcers. These ulcers bleed and may also produce pus and mucus. The mucus may be voluminous enough that it can be seen as it is passed along with the stool.

Irritable Bowel Syndrome. In IBS, there may be increased mucus production by the lining of the intestine. That mucus is then passed in the stool. Mucus is more often associated with diarrhea-predominant IBS than with constipation-predominant IBS or alternating type IBS (IBS-A).

Crohn's Disease. Passing mucus in the stool is a less frequent occurrence in people who have Crohn's disease. If mucus is seen in the stool of a person who has Crohn's disease, it could be associated with developing an anal fissure.

Anal Abscess or Fistula. An abscess is an infection that creates an area filled with pus inside the body. It's a problem that tends to occur more often in people with Crohn's disease, and particularly in the perianal area. Sometimes, in about 50 percent of cases, an abscess will get large enough to form a tunnel between two organs, or between the skin and an organ, which is a fistula. The abscess or fistula may drain mucus into the stool. Abscesses and fistulas will need treatment, potentially being drained and usually with the addition of antibiotics or other medications, particularly if there's a diagnosis of IBD.

Ostomy. Some people who have had ostomy surgery (either ileostomy or colostomy) surgery may find that they pass mucus from their rectum.

Even though stool is leaving the body through the stoma, and not through the rectum and the anus, the rectum is still producing fluids. There could be mucus, which will need to be passed by sitting on the toilet. A build up of mucus could cause discomfort and pressure. 

Bacterial Infections. Bacterial infections, such as those from bacteria such as Campylobacter, Salmonella, Shigella, and Yersinia, may cause mucus to be passed in the stool. A bacterial infection may also cause symptoms of diarrhea, fever, and abdominal cramps. Some bacterial infections may resolve on their own without treatment, but other cases may be serious and require treatment with antibiotics.

If you think you may have contracted a bacterial infection, especially after traveling abroad, contact your physician.

Bowel Obstruction. A bowel obstruction is associated with symptoms of constipation, severe cramps, abdominal distention, and vomiting, as well as the passage of mucus. A bowel obstruction could be caused by one of many conditions such as impacted stool, adhesions (scar tissue), a hernia, gallstones, a tumor, or swallowing a non-food item. Obstructions are typically treated in the hospital, with surgery to remove the blockage being necessary in some cases.

Cystic Fibrosis. Cystic fibrosis is a genetic disorder that can cause the overproduction of mucus in the body. This life-threatening condition most often affects the lungs, but the digestive tract can also be affected. It is usually diagnosed in childhood and is associated with other digestive symptoms such as constipation and abdominal pain.

Unexplained Appearance

For some people, mucus in the stool may be something that happens once, and in that case it might not be a concern. Rather it should be mentioned at the next regular doctor's appointment.

Mucus could be associated with constipation, which is a common problem, and in that case might resolve on its own when the constipation is treated. Dehydration is another common situation that could cause excess mucus in the stool, and again this would likely go away on its own unless the dehydration is a chronic problem. In these cases, treating the underlying problem may help in stopping the passing of mucus.

When to Talk to the Doctor

For anyone who has not already been diagnosed with a condition where passing mucus could be considered a typical symptom, seeing mucus in or on your stool is a reason to see a physician. This is especially true if the mucus is accompanied by other digestive symptoms such as blood in the stool, diarrhea, abdominal pain, constipation, or vomiting.

If mucus in the stool is a fairly regular occurrence because of an already diagnosed condition like IBS or ulcerative colitis, it's still important to monitor it. Marking down what time of day it happens and estimating how much mucus is present (including if it is more or less than in the past) is important. Bringing this information to the doctor will help in finding out what might be causing the increase in mucus. 

Diagnosis

Making a diagnosis when mucus in the stool is a new symptom will start with a careful medical history. A physician will ask what bowel movements have been like in the past and if they've changed recently. Depending on what is suspected of causing the mucus, different types of tests might be ordered.

These could be a stool culture and blood tests, or potentially imaging studies like a CT scan, MRI, or plain x-ray. In some cases, a physician may need to do other testing, such as an endoscopy procedure, to figure out what is happening. But, in many cases, it's not necessary to do invasive testing to determine the cause of the mucus.

A Word From Verywell

The passage of mucus in the stool in the setting of IBS or ulcerative colitis is not necessarily a cause for alarm because it can be a sign of those conditions. However, passing mucus in the stool, especially if it is a new symptom, should still be mentioned to a physician at the next office visit.

Mucus without an underlying cause, such as one of the pre-existing conditions mentioned above, is a change in bowel habits and should be discussed with a physician as soon as possible. 

Sources:

Kornbluth A, Sachar DB; Practice Parameters Committee of the American College of Gastroenterology. "Ulcerative colitis practice guidelines in adults: American College Of Gastroenterology, Practice Parameters Committee." Am J Gastroenterol. 2010;105:501-523.

Sun J, Shen X, Li Y, et al. "Therapeutic Potential to Modify the Mucus Barrier in Inflammatory Bowel Disease." Nutrients. 2016 Jan 14;8. pii: E44.

Zhu L, Huang D, Shi L, et al."Intestinal symptoms and psychological factors jointly affect quality of life of patients with irritable bowel syndrome with diarrhea." Health Qual Life Outcomes. 2015 Apr 18;13:49.

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