Melanin is a natural pigment (dye) found in humans in the skin, hair, retina and iris of the eye, and in the brain. It is the amount of melanin that determines the intensity of human skin coloring, the color of his eyes, and the ability to tan. There are three types of melanin: eumelanin has a brown or black color; pheomelanin is yellow; neuromelanin is a special type of pigment found in the brain. The site of melanin formation in the skin are melanocytes, specialized cells that have many appendages. They capture thyroxine from the blood, a hormone secreted by the thyroid gland. After oxidation, thyroxine is converted to melanin. Then it is transported along the processes of melanocytes to the skin cells, and deposited in them.
All skin nevi can be classified by size: small nevi measuring 0.5 - 1.5 cm; medium nevi measuring 1.5 - 10 cm; large nevi measuring more than 10 cm; if the nevus is located on an entire area of the body, occupying it almost entirely, it is called gigantic.
The following types of nevi are distinguished:
- Border nevus is a simple spot that does not rise on the skin, or protrudes slightly above its surface. The border nevus has clear contours and a brown color. It can have different sizes and be located on different parts of the body. In this type of melanoform nevus, a cluster of cells with pigment is located between the upper (epidermis) and middle (dermis) layers of the skin. This arrangement of pigment, combined with an uneven surface rising above the skin, is referred to as an Intraepidermal nevus. Most often, such a nevus is located on the head or neck. In most cases, an intraepidermal nevus appears at the age of 10 to 30 years.
- Intradermal nevus is the most common type of melanoform nevus. It is so called because the accumulation of pigment cells is located in the thickness of the middle layer of the skin – the dermis, so their color differs little from the color of the surrounding skin and they are noticeable due to their height.
- Pigmented complex nevus of the skin. Such a nevus rises above the skin (symmetrical papule) and can have a different color, from light brown to almost black, with a stronger pigmentation in the center. The surface is smooth or slightly papillomatous. It often grows coarse hair.
- Mixed nevus can be found on any part of the body. It protrudes above the surface of the skin, with a smooth or uneven, bumpy surface. It is almost always located on the head or neck, very rarely on the torso. Over time, it separates from the skin, as it were, and is located on the leg. It often then turns into a papillomatous nevus (warty nevus). It forms a large number of irregularities, folds and crevices in which dead cells of the upper layer accumulate. Pathogenic organisms can accumulate here, which then lead to infectious processes.
- The blue nevus has a characteristic color, as it is associated with melanin deposits under the skin. Blue nevi are characteristic mainly of Asian nationalities. They rise slightly above the skin, are dense to the touch, their surface is always smooth, and hair never grows on it. The blue nevus has a small size, most often no more than five millimeters.
- Basal nevus also has the appearance of a mole, but most often it has a normal flesh color. This is an pigment–free nevus.
- Seton's nevus (Setton's nevus, Sutton's nevus, halo nevus) is a special type of dermal nevus when there is a patch of skin around the pigment spot that is completely devoid of pigment. The origin of such nevi has not yet been fully studied. They are often combined with vitiligo (loss of skin pigments), melanomas. Most often, there is a slight inflammation in the skin in the area of the halo nevus.
- Nevus of Ota. It is located on the face, on the one hand, in the form of "dirty" spots.
- Nevus Ita resembles nevus Ota, but it is located under the collarbone, on the chest, in the area of the shoulder blade and neck. Both of these varieties are found mainly among representatives of Asian peoples.
- Papillomatous nevus (warty nevus). A papilloma-like nevus is often large, located on the head or at the back of the neck, but it can be located in other places. It has an uneven surface, like a wart. Hair often grows on it.
- Reed's nevus is a black
or dark
brown, convex, fast-growing neoplasm.
They occur mainly in women.
- Nevus Spitz (nevus Spitz, juvenile nevus) – raised, domed moles. Such pink neoplasms mostly grow at a young age — up to 20 years, about a third of patients are children under 10 years of age.
- Meyerson's nevus is a nevus surrounded by a red rash (eczema). They are mainly found in men over 30 years of age, and in women they are 3 times less common.
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Becker's nevus (hairy epidermal nevus) – it occurs more often in boys and boys aged 10-15 years. First, several small spots form on the body, which are light brown or brown in color, and are located nearby. Then they merge and form spots with uneven contours up to 20 cm in size. After that, the spots acquire an uneven warty surface and become covered with hair. It is believed that the release of large amounts of male sex hormones, androgens, into the blood leads to the growth of Becker's nevi.
- Linear nevus is a neoplasm that appears from birth. It consists of many small nodules, from light to almost black in color, which are located on the skin in the form of a chain. A linear nevus can take up only a couple of centimeters, or maybe the entire arm or leg. Sometimes hair grows on it.
- Nevus of the eye is a pigmented nevus that is located on the iris. It is clearly visible in the form of a spot, which can have different sizes and shapes. Also, the nevus of the eye may be on the retina: in this case, it is detected only during an examination by an ophthalmologist.