Causes of Stool Mucus in Bowel Movements

Mucus is a thick somewhat slimy substance that is produced in many parts of the body. It plays several important roles but most of the time its main purpose is to moisturize tissue and provide lubrication for movement. A significant amount of mucus is produced by tiny mucus-producing cells in the lining of the small and large intestine to help with the movement of digested food and stool through the bowels.

Normally there is a small amount of mucus passed out in the stool. It can also help with the easier passage of stool out of the rectum. However, it is barely noticeable. Most of the time the concern arises when there is significant mucus in the stool. Due to the thick, slimy and stringy nature of mucus, it is sometimes even mistaken for parasitic worms. Usually the mucus coats the stool and anus but does significantly change the consistency of the stool unless diarrhea is present.

Slimy, oily or greasy stools may not always be due to mucus. Instead the grease may be due to undigested fats in the digestive tract that is then passed out with the stool. This is known as steatorrhea. It occurs when the food passes through the gut too quickly for the fat to be digested or where there is some underlying problem with fat-digesting enzymes which allows the fat to pass through into the stool rather than being absorbed.

Causes of Mucus in Stool

Excessive mucus in the stool is usually associated with inflammatory conditions of the bowel. The inflammation of the bowel wall causes the mucus-producing cells and glands to increase mucus secretion. When mucus is visible in the stool it is usually emanating from the lower half of the small intestine and large intestine. Therefore it is more likely that the disease lies in these areas. Mucus secreted higher up in the digestive tract may be digested or mixed with stool so it is not as easily available.


Hemorrhoids is a common cause of mucus in the stool. It is a condition where the veins of the rectum and anus become inflamed and swollen. These veins may sometimes protrude out of the anus. The inflammation triggers excessive mucus production and since it is where the stool is about to exit, the mucus is not mixed in the stool but instead coats it.

Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a functional bowel disorder meaning that it is due to some alteration in normal bowel function. There is no noticeable inflammation or other disease mechanism that can be identified within the bowels in IBS. Symptoms like mucus in the stool may occur especially with the diarrhea-predominant variety of IBS.

Inflammatory Bowel Disease

Inflammatory bowel disease (IBS) is another common bowel condition and should be confused with IBS. In IBD there is inflammation of the bowel wall sometimes with the formation of ulcers (open sore). It is a chronic condition marked by periods of acute exacerbations. Mucus in the stool along with diarrhea is a common symptom especially during acute episodes.

Intestinal Parasites

Infestation of the intestines with parasites, including parasitic worms and certain protozoa, may also trigger excessive mucus production. Some of these infestations trigger minimal symptoms and even the mucus in the stool may not always be present. Mucus is most likely linked to intestinal inflammation. Sometimes it can be the only symptom of an infestation.

Polyps and Cancer

Mucus in the stools may also be linked to conditions such as intestinal polyps and bowel cancer. As with most conditions, the presence of mucus in the stool is not a reliable indicator of polyps or cancer. Certain mucus-producing tumors of the digestive tract or associated organs could contribute to the presence of mucus in the stool.


Gastroenteritis, or a tummy bug as it is often referred to, causes inflammation of the stomach and bowels. It is usually caused by viruses (stomach flu) but bacteria and protozoa may also be responsible. These microbes invade and destroy the cells lining the bowel. Sudden onset of nausea, vomiting, diarrhea and abdominal cramps are typical symptoms. It usually resolves on its own within a few days.

Food Poisoning

Various toxins, usually produced by bacteria, can cause irritation and inflammation of the digestive tract. This usually leads to diarrhea, abdominal cramps or pain, nausea and vomiting. The inflammation of the bowels may also lead to excessive mucus production which can cause mucus in the stool.

Food Intolerances

The human body’s ability to metabolize food requires the presence of digestive enzymes to break it down and the bowel lining allows it to be absorbed into the body. In food intolerances these digestive enzymes are deficient thereby impairing the ability to chemically break down foods. In malabsorption syndromes certain nutrients cannot be absorbed into the body. Apart from diarrhea and cramps, mucus in the stool may also be present.

Small Intestinal Bacterial Overgrowth

Small intestinal bacterial overgrowth is a condition where certain bacteria enter the small intestine and its population increases significantly within the bowels. Normally these are the normal intestinal bacteria found in the large intestine which are usually absent in the small intestine. It may occur in a number of diseases where the valve separating the small and large intestines malfunction or when the immune defenses drop.


Diverticulitis is the inflammation of outpouchings that form in the intestine. These outpouchings are known as diverticula. It can become inflamed or infected. Diverticula are mainly seen later in life particularly in people who are obese. It usually does not cause any symptoms. Abdominal pain, nausea, vomiting, fever and changes in bowel habit occur with diverticulitis and mucus may be present in the stool.

Cystic Fibrosis

Cystic fibrosis is a very serious disorders that affects mucus-producing and other glands in the body. It mainly involves the lungs and digestive tract. Secretions from these glands become thick and sticky and it is due to a genetic defect. The stools are greasy and have an offensive odor and in newborns it can cause an intestinal blockage.

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