Melanosis coli, also known as pseudomelanosis coli, is a benign pigment disorder in which the lining of the large intestine, or colon, turns black or brown. The condition is benign, meaning that it does not pose any danger to a person’s health.

Some research suggests that melanosis coli may even facilitate the diagnosis of benign and cancerous colon polyps.

This article explores the signs and symptoms of melanosis coli, as well as its causes, diagnosis, treatment, and prevention. It also discusses the outlook for people living with the condition.

An abstract image of the intestines.Share on Pinterest
SEBASTIAN KAULITZKI/SCIENCE PHOTO LIBRARY/Getty Images

Melanosis coli is a pigment disorder that does not cause any symptoms, so a person might never know that they have the condition. A doctor will often only detect melanosis coli if they see it when carrying out a colonoscopy or sigmoidoscopy for another reason.

A colonoscopy is a procedure that involves the use of a colonoscope. This device consists of a flexible tube with a camera and light attached, which allows the doctor to check for inflammation and other abnormalities in the colon and rectum. A sigmoidoscopy is a similar, less intrusive procedure that allows the doctor to view only the lower part of the colon.

Doctors typically detect melanosis coli in individuals over the age of 45 years, although the condition can also occur in younger people. It appears to affect males and females equally.

Below are some possible causes of melanosis coli.

Simulant laxative use

Melanosis coli often occurs as a result of using stimulant laxatives for an extended period. This class of laxatives irritates the intestinal nerves, causing the intestines to contract and push stool out of the body.

There are several types of stimulant laxatives. Anthraquinones are the type most associated with melanosis coli. Examples include:

  • senna
  • aloe
  • rhubarb
  • cascara sagrada
  • buckthorn

A 2015 case study notes that anthraquinones can trigger the death of mucosal cells within the lining of the colon. The dead cells become discolored, resulting in abnormally pigmented areas of colon tissue.

Topical psoriasis treatment

Melanosis coli can also develop in response to using topical psoriasis treatments containing a natural derivative of anthraquinone called anthralin.

Diet

Anthraquinone is a plant compound that is present in certain vegetables and herbs. A person may develop melanosis coli due to the excessive consumption of herbal products containing anthraquinones.

NSAID use

In a 2017 study investigating 219 people with melanosis coli, two participants had no history of laxative use but regularly used nonsteroidal anti-inflammatory drugs (NSAIDs). Examples of NSAIDs include:

Inflammatory bowel disease

A 2022 review notes that melanosis coli may be present in some individuals with a form of inflammatory bowel disease (IBD) called ulcerative colitis.

A 2015 case study notes that melanosis coli is a benign condition that is not associated with colon cancer. The authors add that melanosis coli may, in fact, help doctors detect both benign and malignant colon polyps, as these growths do not take on the darker pigmentation of the surrounding tissue.

A 2018 study compared polyp detection rates and colon cancer diagnoses in participants with and without melanosis coli. The researchers found that the condition was associated with enhanced polyp detection but not increased diagnosis of colorectal cancer.

Most melanosis coli diagnoses occur during or after a colonoscopy or sigmoidoscopy for another reason.

A doctor should be able to detect the characteristic pigmentation changes during either of these procedures. However, they may take a tissue biopsy to confirm the findings and rule out more serious medical conditions.

According to a 2020 review, melanosis coli is a reversible condition. The authors state that a person who has melanosis coli and takes anthraquinone laxatives should stop taking the laxatives to help reverse the condition.

The authors also state that surgery should only be a consideration in cases where the melanosis coli occurs alongside a serious malignancy.

A 2021 case study reported on a woman who developed melanosis coli due to laxative use following a treatment called peritoneal dialysis. In this case, the treatment for melanosis coli involved stopping the laxatives and taking a probiotic.

It may not always be possible to prevent melanosis coli. However, avoiding laxative use could help reduce the risk of developing the condition.

People usually take laxatives due to constipation. A person can take steps to help prevent constipation. These include:

  • drinking plenty of water
  • refraining from drinking alcohol
  • eating plenty of high fiber foods
  • taking a fiber supplement
  • partaking in regular physical activity
  • trying to have bowel movements at the same time every day
  • stopping taking certain medications and supplements that cause or contribute to constipation, but only if a doctor states that it is safe to do so

If a person continues to experience constipation after trying all of the above, they should consult a doctor. The doctor may run tests to determine the cause, and they may recommend prescription treatments.

Surgery may be an option if the constipation relates to a lack of function in the colon muscles or a rectal prolapse.

Melanosis coli is a pigmentation condition that does not cause any symptoms. The condition is benign, meaning that it is not associated with any risk to a person’s health.

Most cases of melanosis coli are due to the regular use of anthraquinone laxatives to treat chronic constipation. A person who experiences chronic constipation may develop symptoms and complications related to the constipation, such as hemorrhoids and fecal impaction.

Melanosis coli is a benign condition that causes black or brown discoloration of the colon wall. It usually occurs as a result of using anthraquinone laxatives.

People with melanosis coli may never know that they have the condition, as it does not cause any symptoms. Most doctors diagnose the condition during or following colonoscopy or sigmoidoscopy procedures for an unrelated reason.

Researchers have not identified any association between melanosis coli and colon cancer. In fact, some research suggests that melanosis coli can help doctors detect benign and malignant colon polyps.