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Among the benign pigmented lesions on the skin - nevi (from the Latin naevus - mole) - a warty nevus protruding above the skin surface is distinguished, which, as the name implies, looks like a wart.
In dermatology - because of this external similarity - such a mole is often defined as a verrucous warty nevus (in Latin verruca - a wart) or as a papillomatous nevus, since the appearance of warts is triggered by the human papillomavirus (HPV). 
Among all types of moles, the incidence of warty nevi in the population does not exceed 6%. The prevalence of linear verrucous epidermal nevus is estimated at 1: 1000 live births. 
Causes of the verrucous nevus
Multiple comparative definitions in medicine can be misleading for patients. But the warty epidermal nevus , which forms in the upper layer of the skin (epidermis), has nothing to do with warts (caused by viruses of the Papillomaviridae family) .
Like other types of moles on the body , a verrucous nevus in a child or adult
These nevi are the result of overgrowth (mitosis) of special dendritic cells of the basal layer of the epidermis and hair follicles - melanocytes, which contain and produce the dark pigment melanin, which provides photoprotection of skin cells.
More information in the materials:
In addition to heredity and features of intrauterine development, it is customary to refer to the risk factors for the appearance of warty nevi as a negative effect on the cells of the epidermis of ultraviolet rays, with prolonged exposure to which not only epidermal melanocytes, but also skin keratinocytes (the main cells of the outer layer of the dermis) can become more active. 
The pathogenesis of the development of epidermal nevi similar to warts is chromosomal mosaicism, which can be caused by:
- mitotic recombination during embryogenesis of melanocytes from neural crest cells (melanoblasts);
- violation of the movement of mature melanocytes to keratinocytes;
- changes in the differentiation of keratinocytes;
- mutations of genes encoding melanosome proteins (synthesizing melanin) or melanogenic enzymes and hormones that regulate melanocyte proliferation and melanin synthesis. 
All details in publications:
Symptoms of the verrucous nevus
The characteristic signs or symptoms of a warty nevus are the presence on the skin of a fairly convex, delimited formation of a dense structure (all shades of brown, dirty gray or bluish-purple outflow), the surface of which is distinguished by the presence of tubercles. These irregularities are the result of the alternation of raised and slightly deepened areas of the thickened epidermis with steam or orthohyperkeratosis, that is, an increased level of keratin in nucleated and non-nucleated epithelial cells.
Such a nevus can have a wide base (leg), which even more resembles a wart. Another sign may be hair on a warty nevus.
With the formation of several areas of excessive proliferation of melanocytes, merging in the form of an extensive elongated thickening and hyperkeratosis of the epidermis, a linear warty nevus is diagnosed.
It should be borne in mind that warty nevi are not associated with inflammatory processes, however, it is extremely rare in infancy or early childhood (and even less often in adults) that an inflammatory linear warty nevus is possible. It is defined by dermatologists as a separate form of a nevus with a characteristic one-sided localization (more often on the left - on the skin of the extremities) and a histological appearance: with thickening of the epidermis in the form of plaques and thickening of its prickly layer (acanthosis), as well as the presence of inflammatory infiltrates in the stratum corneum of the epidermis (which can have a spongy appearance)., 
Complications and consequences
Possible complications and consequences are associated with damage to the nevus, in which there can be bleeding and inflammation.
But a change in its color, shape or a sharp increase in size is a serious reason for visiting a dermatologist.
Over time, the mole may grow larger, and a neglected verrucous nevus can be significant in size.
In some cases, a warty nevus itches, for more details see - Why does a mole itch and what to do?
And differential diagnosis is carried out with skin papilloma and other epidermal formations. In particular, a warty nevus or keratoma (either senile or follicular - focal keratinization of the epidermis in the area of the hair follicles), as well as dysplastic nevus, cystic epithelioma, Darrieus-Ferrand tumor, verruciform acrokeratosis, pigmented melanoma are differentiated.
There are no special preventive measures against the appearance of moles on the body.
In the presence of a warty nevus, which is a benign formation, the prognosis is favorable.