Melanosis is a broad term for conditions in which excess pigment deposits in body tissues, causing darkened patches on the skin, inside the mouth, in the colon, or in the eye. It is not a single disease but a category that includes several distinct conditions, most of which are benign. The type of melanosis you have depends on where the pigmentation appears and what triggered it.
Types of Melanosis by Location
Because melanosis simply means “abnormal pigmentation,” doctors almost always use a more specific name that tells you which part of the body is involved. The most commonly diagnosed forms are melanosis coli (colon), smoker’s melanosis (mouth), ocular melanosis (eye), vulvar melanosis (genital skin), Becker melanosis (body skin), and Riehl melanosis (face). Each has different causes, different appearances, and different implications for your health.
Melanosis Coli
Melanosis coli is a dark discoloration of the lining of the large intestine. It is caused by regular use of stimulant laxatives that contain plant-based compounds called anthraquinones, found in products like senna and cascara. When these compounds reach the large intestine, they become active and damage the cells lining the colon wall, triggering programmed cell death. As those cells break down, they produce a dark pigment called lipofuscin. Immune cells called macrophages swallow the debris and settle into the deeper tissue layers, giving the colon wall a brownish or blackish tint that is visible during a colonoscopy.
Melanosis coli is considered harmless and does not cause symptoms on its own. It is almost always discovered incidentally during a colonoscopy performed for another reason. The discoloration is reversible: it typically fades within 6 to 12 months after you stop taking the laxative. There is no evidence that melanosis coli itself raises your risk of colon cancer, though its presence signals long-term laxative use, which your doctor may want to discuss.
Smoker’s Melanosis
Smoker’s melanosis refers to flat, brownish patches that develop on the gums and other surfaces inside the mouth in response to tobacco use. It affects roughly 25 to 31 percent of smokers. In the vast majority of cases (about 95 percent), the pigmentation appears on the lower jaw, most often on the gum tissue near the front teeth and canines on the lip side.
The discoloration is caused by nicotine and other chemicals in tobacco smoke stimulating the pigment-producing cells in the oral lining. It is painless and benign. The patches often lighten or resolve after a person quits smoking, though this can take months to years.
Ocular Melanosis
Ocular melanosis is a congenital condition in which excess pigment cells accumulate in the deeper layers of the eye, specifically the sclera (the white of the eye) and the tissue beneath it. It is present from birth and almost always affects only one eye. Signs include a slate-gray or bluish discoloration of the white of the eye, a difference in iris color between the two eyes, and increased pigmentation in the back of the eye.
When the same pigmentation also extends to the skin around the eye and forehead, the condition is called oculodermal melanocytosis, or nevus of Ota. Unlike most other forms of melanosis, ocular melanosis carries a small but real cancer risk. The lifetime risk of developing a melanoma inside the affected eye is approximately 1 in 400. People with this condition are also at increased risk of glaucoma in the affected eye, so regular eye exams with pressure checks are important.
Vulvar Melanosis
Vulvar melanosis produces flat, painless dark spots on the vulvar skin and mucosa. The spots range from tan-brown to black, are often irregularly shaped with poorly defined borders, and can appear as a single patch or multiple patches. About 70 percent of these spots measure less than 10 millimeters across. Despite their irregular appearance, they are benign.
The concern with vulvar melanosis is that it can look similar to early melanoma at first glance. The key distinction is color. Benign vulvar melanosis shows shades of brown and sometimes black. If gray, blue, red, or white colors appear within a spot, that raises suspicion for melanoma and typically prompts a biopsy. Any spot that changes noticeably in size, shape, or color over time should also be evaluated.
Becker Melanosis
Becker melanosis, also called Becker nevus, is a patch of darkened skin that usually appears during adolescence, most often on the shoulder, upper back, or upper arm. It tends to be one-sided and is sometimes accompanied by coarser or thicker hair growth within the patch. The right side of the body is affected slightly more often than the left. Becker melanosis is entirely benign and does not become cancerous. It is thought to be influenced by hormones, which explains why it often first appears around puberty and is more common in males.
Riehl Melanosis
Riehl melanosis is a form of pigmented contact dermatitis that appears as grayish-brown discoloration on the face, particularly the forehead, temples, and cheeks. It develops as an allergic reaction to contact allergens, most commonly ingredients found in cosmetics, fragrances, and textiles. Specific triggers that have been identified through patch testing include certain skin-lightening creams, preservatives like cetrimide, and antioxidant additives like gallate mix.
The underlying mechanism is a delayed allergic reaction in which immune cells attack pigment-containing skin cells. The released pigment drops into deeper skin layers, producing a persistent grayish-brown hue. Sun-reactive chemicals in cosmetic products can worsen the process. Identifying and avoiding the triggering product is the most important step in treatment, after which the discoloration gradually improves, though it can take many months.
Melanosis vs. Melanoma
The word melanosis sounds alarming because of its similarity to melanoma, but the two are fundamentally different. Melanosis refers to an excess of normal pigment in tissue. Melanoma is a cancer of the pigment-producing cells themselves. Most forms of melanosis carry no cancer risk at all.
Dermatologists use the ABCD criteria to evaluate whether a pigmented spot warrants concern: asymmetry, border irregularity, color variation, and diameter. These features alone do not diagnose melanoma, but a spot that scores high across multiple criteria, especially one that includes unusual colors like blue, gray, or white, is more likely to need a biopsy. The presence of multiple brown shades in a flat, stable spot is far more consistent with benign melanosis.
Treatment Options
Most melanosis requires no treatment because it is harmless. For melanosis coli, simply stopping the laxative resolves the condition. For smoker’s melanosis, quitting tobacco is the primary intervention.
When melanosis on visible skin causes cosmetic concern, several options can help. Topical lightening agents are usually the first step. The most widely used is hydroquinone at concentrations of 2 to 5 percent, which works by suppressing the enzyme responsible for pigment production. Other topical options include azelaic acid, kojic acid, and tretinoin (a vitamin A derivative), all of which can reduce pigmentation over weeks to months of consistent use. Combination creams that pair hydroquinone with tretinoin and a mild corticosteroid have shown the best results for stubborn pigmentation.
For cases that don’t respond well to topical therapy, laser treatments can target pigment in the skin. These range from intense pulsed light systems to lasers specifically tuned to break apart melanin. Newer picosecond lasers deliver energy in extremely short pulses, reducing the risk of post-treatment darkening. Most dermatologists recommend combining laser treatment with ongoing topical therapy to prevent the pigmentation from returning.