What is Melanosis?

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  • Written By: Doug Donald
  • Edited By: A. Joseph
  • Last Modified Date: 15 November 2018
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Melanosis is a condition in which the skin or other tissues are abnormally darkened by excessive deposits of the pigment melanin. This hyperpigmentation is also known as melanism and is caused by a disorder in melanin production or metabolism the body. The disorder occurs in humans and other animals.

Found in most living things, melanin is the pigment that determines skin color in humans. People who have higher levels have darker skin. Freckles and moles are the result of localized melanin concentrations in the skin. It is also present in human hair and eyes.

Melanosis occurs when too much melanin is produced and deposited in the tissues of the body. Common types of this condition are melanosis coli, smoker’s melanosis and ocular melanosis. With the exception of the last, most types are benign conditions, and many correct themselves when causal factors are removed.

When dark pigment deposits on the lining of the colon or large intestine cause a brown or black discoloration, it results in melanosis coli. The condition is a bit of a misnomer because there is no melanin in this particular pigment. This discoloration, which has no known connection with colon cancer, is commonly caused by the chronic overuse of laxatives. It has no symptoms and usually is observed or diagnosed during a colonoscopy or sigmoidoscopy. When a person stops using laxatives, the discoloration of the colon will lessen and eventually disappear over time.


Smoker’s melanosis is a hyperpigmantation found in the mouth. It is generally associated with smoking but can be found in some non-smokers, it appears as irregular dark patches in the tissues underlying the mucous membranes. The discolorations will almost always disappear when the person stops smoking. This condition is benign and is not a precursor of mouth cancer.

Ocular melanosis is also known as melanosis oculi and affects approximately one out of every 5,000 people. This is a congenital condition that is a known risk factor for a cancer of the eye called uveal melanoma. It can also cause a condition called pigment dispersion syndrome, in which fluid cannot properly drain from the eye. The increased fluid results in greater pressure in the eye and can lead to glaucoma. This condition should be monitored closely by an ophthalmologist.

Oral melanosis is the development of dark spots inside the mouth. The spots are similar to those resulting from smoking, but they are not caused by it. It is most common in dark-skinned people.

The development of dark patches on the skin or other tissues should always be examined by a medical professional. He or she will be able to determine whether there is cause for concern. If the diagnosis is melanosis or melanism, the condition probably is harmless.


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Post 2
@irontoenail - If that's not sexy, then melanosis coli is really gross. I mean, I understand that sometimes people have to take laxatives for a long time to deal with a medical condition, but I think most of the time it would be because they are abusing them in order to try and lose weight.

So I guess it's kind of a good thing that there's a definite sign the doctors can see that will identify people who are doing this, since it can cause other kinds of more severe damage.

I wonder if it ever effects people who have chronic diarrhea from other causes?

Post 1

I didn't know you could develop smoker's melanosis. I'm sure if I had developed dark patches in my mouth while I was smoking, cancer would be the first thing to spring to mind. People don't realize that it causes cancer of the mouth, but it does.

Yet another reason I'm glad I gave up. It wouldn't be terribly sexy to have random dark patches in your mouth.

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