It is generally accepted that the causes of moles on the body that can be formed in any of its areas are covered in benign local spread of melanocytes - dendritic cells of the basal layer of the epidermis.
These are the only cells that synthesize protecting the skin from ultraviolet rays and conditioning the skin color, hair and eye pigment melanin.
By structure and properties melanin is a UV-filtering biopolymer, which is obtained during a multistage biochemical transformation of the α-amino acid of tyrosine; the pigment is deposited in melanocyte organelles - melanosomes, but falls into the upper layers of our skin due to keratinocytes.
Accumulating in one place, melanocytes form birthmarks, and their average number in one person is from 30 to 40.
Key causes of moles in adults and children
For the sake of finding out the true cause of the appearance of moles by biologists and physicians, numerous biochemical and genetic studies have been and are being conducted (and will be carried out).
In this case, specialists remind that skin is the most important multifunctional organ, the bookmark of which occurs in the process of embryogenesis, that is, during the development of the human embryo.
Most moles appear during the first 20-30 years of a person's life, and, according to statistics, only one in every 100 babies at the time of birth has birthmarks. And the reasons for the appearance of moles in a child, that is, congenital nevuses (in Latin naevus means "birthmark") is associated with a slight defect in embryonic development in the first twelve weeks of pregnancy.
Melanocytes producing skin pigment are formed from neural crest cells of melanoblasts, which in the initial stages of embryogenesis spread out along the upper (dorsal) part of the neural crest into various parts of the body (the flat epithelium of the skin and mucous membranes, hair follicles, and the tissue of the arachnoid membrane of the brain). In the basal layer of the epidermis, melanoblasts ripen to melanocytes capable of producing melanin. Defect is believed to lead to accelerated proliferation of melanocytes.
This means that their excess is formed, and the "excess" melanocytes spread in the skin not evenly, but collect together-nests, clusters, islets-in the uppermost layer of the skin and even protrude out of it.
Recent studies slightly clarify the picture. The fact is that some melanocytes arise from melanoblasts migrating ventrally - along the lower surface of the neural tube, and then along the nerves. These precursor cells of melanocytes give rise to the peripheral nervous system and adrenal medulla. Thus, they find themselves in the shells of nerves and axons, among the Schwann cells, and are capable of producing melanocytes after birth.
There is scientific evidence that melanocytes in moles are mutated into so-called dermal nevus cells - cutaneous nevus cells. This variant of melanocytes differs from usual with its size, cytoplasmic volume and lack of shoots (dendrites). They are usually located at the border of the transition of the dermis into the epithelial tissue, and depending on the degree of maturity can be further classified as epithelioid, lymphocytic and neuroid. It is claimed that the nevus cells are able to migrate, penetrating into the lymph nodes and even into the thymus gland (thymus), where the immunocompetent cells - lymphocytes form and mature.
To date, it has been established that in 60% of cases the causes of the appearance of moles in adults and children are hereditary. There are already more than 125 different genes that regulate pigmentation, either directly or indirectly. Many of these genes control the differentiation of melanocytes or influence the biogenesis and function of melanosomes, as well as the involvement of the pigmentation and proliferation of epithelial cells of hormones, growth factors, transmembrane receptors (EphR, EDNRB2, etc.), biochemical processes, transcription factors (such as MITF, Sox10, Pax3, etc.). The interaction of the totality of all of the above enumerates the causes of the appearance of new birthmarks.
By the way, about hormones. Hormonal changes during pregnancy and in diabetic patients often contribute to the formation of moles. And the hormonal causes of the appearance of moles in a child and adolescent explain, primarily, the activity of hormones and biochemical growth factors (for example, SCF factor of stem cells): because children grow and the area of skin is constantly increasing. Also in the growing organism, melanocortins produced by the pituitary gland are very active, hormones that purposefully stimulate the synthesis of melanin (they also affect the production of corticosteroids in the adrenal cortex and lipid metabolism in the adipose tissue cells).
Under the influence of solar radiation, the synthesis of melanin rises (and we see this when sunburn appears). All this is the result of tyrosinase activation in melanocytes, which provides enhanced protection of the skin from UV. Some scientists suggest that excessive sun exposure can play a role in the formation of acquired moles. So far, the biomechanics of the interaction between the genetic structure and the overall effect of ultraviolet rays has not been elucidated. However, in favor of the fact that this is so, the practical absence of moles on the buttocks indicates a practical ...
Causes of moles on the neck, face and armpits
Practically everyone is interested in answers to three questions:
Are there any special reasons for the appearance of birthmarks on the face?
What are the causes of moles on the neck?
What are the reasons for the appearance of the birthmark armpits - in such an uncomfortable place, which, in general, and the sun is not exposed?
We will try to answer them, relying on what is already known to clinical dermatology regarding the formation of epidermal nevi of the indicated localization.
Melanocytes are located between basal keratinocytes in an approximate ratio of one to ten and distribute melanin through their elongated processes (dendrites), as well as through direct cell contacts. As you know, the keratin cells of the skin in the upper layers of the epidermis replace each other quickly enough and, rising upwards (to the horny layer of the skin) carry away the captured melanin - to form a barrier against ultraviolet rays.
At the same time, in various parts of the epidermis, the melanin content and the number of cells producing it are different: in the skin of the head (including the face), as well as the necks and arms of melanocytes, twice as much as in other parts of our body. Obviously, this is due to the fact that these areas are much more often open, and they get the most sun rays.
Among the yet unproved versions of the cause of the appearance of moles on the face there is the assumption that the process of formation of non-vascular skin cells is promoted by increased metabolism in epidermal cells - due to the stressful effects of changes in temperature and air humidity on the face skin, as well as constant stretching and contraction of the skin by facial mimic muscles .
In addition, there is an opinion that there may be reasons for the appearance of moles on the neck associated with disorders in the formation and distribution of melanin in parts of the epidermis directly above the nerves of the cervical plexus (see above - the migration of melanoblasts in embryo development). These are the branches of the motor, skin and diaphragm nerves, which are connected by loops and located on the neck (rear, front and both sides).
But the reasons for the appearance of the birthmark of the armpit, the researchers are inclined to see the presence in the skin of the axillae of hair bulbs and glands - sweat and apocrine. But the specific mechanism of the formation of nevi axillas has not yet been studied. Moreover, it remains unknown how the flow of melanocytes into the epidermis is controlled, although, of course, the regulatory scheme of this process exists.
The causes of the appearance of pink and red moles
The most likely reason for the appearance of red moles is that the "body" of a nevus can be not only melanocytes, but also cells of the epidermal connective tissue, accessory fibers, and also vascular elements. The so-called vascular nevuses (nevus vascularis) are manifested by various reddish swellings or spots on the skin due to the hypertrophy of the capillaries - the proliferation of blood vessels in the skin.
In addition, there may be a link in the lack of coagulation factors and vitamin K, which leads to increased bleeding when the walls of cutaneous capillaries, partially trapped in the formation, are damaged.
According to dermatologists, red moles are typical for such diagnoses as autoimmune rheumatoid arthritis or systemic lupus erythematosus.
The causes of the appearance of red convex moles are similar. At the same time, their "bulge" (as in the case of brown moles) is the result of the fact that melanocytes are often located much higher than the dermoepidermal junction and are localized in the upper layer of the epidermis, including in the granular zone and the stratum corneum.
The causes of the appearance of pink and red moles do not exclude the influence of the features of the composition of the produced melanin. Melanin can be either brownish-black (eumelanin), or reddish-orange (pheomelanin). In the latter case - especially in red-haired and natural blondes - birthmarks are often light beige or pink.
The causes of the appearance of hanging moles
The fact that the cause of the birth of a birthmark on the leg, as well as the causes of the appearance of hanging moles on the neck are thoroughly studied, it is unnecessary to speak. Although much attention is paid to the study of the etiology of this species of epidermal nevi.
Thus, the association of melanocytic nevus with eccrine sweat glands is revealed, which is expressed not only in the body's grasp of the mole of the gland itself (which can be in the center of the mole), but also in the exit of the nevus cells in the form of a node outward through the eccrine channels.
In other cases, the infiltration feature leads to a linear structure of the distribution of intradermal nevus cells. Going beyond the dermoidermal border and the papillary layer of the skin, a group of such cells penetrates the surface, expanding part of the epidermis between the fibers of the collagen. Moreover, intradermal nevus cells can form a pigmented domed or papillomatous papule (up to 1 cm in diameter), equipped with a foot. It is also possible to have a molluscous form with a wide base, with a color ranging from light brown and black to whitish or pinkish-red.
Hanging moles can be formed anywhere, however their "favorite places" are the neck area, armpits and skin in the crotch area.
In the middle of the last decade, researchers at King's College in London examined 1200 nonidentical female twins at the age of 18 to 79 and found that those who had more moles on the body also had stronger bones, that is, they are less likely to develop osteoporosis. In addition, in older women with more than 60 birthmarks, the skin was less wrinkled and they looked younger than their years ... It turned out that in people with a large number of birthmarks, the chromosomes have unusually long telomeres - the end parts of the DNA polymerase, which prolongs the period of active replication and pushes away many age processes in the body.
And dermatologists advise - regardless of the time and cause of moles - with any changes in epidermal nevuses refer to specialists, since the risk of developing skin cancer associated with the presence of moles, is high enough.
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Medical expert editor
Portnov Alexey Alexandrovich
Education: Kiev National Medical University. A.A. Bogomolets, Specialty - "General Medicine"
Why should you know how dangerous and non-dangerous changes in moles look like ? Because birthmarks (melanocytic nevi) are found in most people, moles are of several types and can vary, and some of them increase the risk of developing this type of skin cancer
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