What are Nevi, or Moles

Nevi, or moles, are benign tumors composed of nevus cells that are derived from melanocytes. The well-publicized increase in the incidence of melanoma has stimulated the layperson's interest and concern about pigmented lesions.
Many myths surround moles; for example, that hairs should not be plucked from moles or that moles should not be removed or disturbed. These myths should be clarified.
Nevus cells.
The nevus cell differs from melanocytes in a number of ways. The nevus cell is larger, lacks dendrites, has more abundant cytoplasm, and contains coarse granules. Nevus cells aggregate in groups (nests) or proliferate in a nonnested pattern in the basal region at the dermoepidermal junction. Nevus cells in the dermis are classified into types A (epithelioid), B (lymphocytoid), and C (neuroid). Through a process of maturation and downward migration, type A epidermal nevus cells develop into type B cells and then into type C dermal nevus cells.
Incidence and evolution.
Moles are so common that they appear on virtually every person. They are present in 1% of newborns and increase in incidence throughout infancy and childhood, reaching a peak at puberty. Size and pigmentation may increase at puberty and during pregnancy. A few may continue to appear throughout life. Nevi may occur anywhere on the cutaneous surface. There is a strong correlation between sun exposure and the number of nevi. Acquired nevi on the buttock or female breast are unusual.
Nevi vs. melanoma.
Nevi exist in a variety of characteristic forms that must be readily recognized to distinguish them from malignant melanoma. Except for certain types, such as large congenital nevi and atypical moles, most nevi have a very low malignant potential.
Nevi vary in size, shape, surface characteristics, and color. The important fact to remember is that each individual nevus tends to remain uniform in color and shape. Although various shades of brown and black may be present in a single lesion, the colors are distributed over the surface in a uniform pattern.
Melanomas consist of malignant pigment cells that grow and extend with little constraint through the epidermis and into the dermis. Such unrestricted growth produces a lesion with a haphazard or disorganized appearance, which varies in shape, color, and surface characteristics. Nevertheless, the characteristics of uniformity cannot always be relied on to differentiate benign from malignant lesions because very early melanomas may appear quite uniform, having a round or oval shape with a uniform brown color.
Examination with a hand lens.
Careful inspection of suspicious lesions with a powerful hand lens may reveal irregularities in the border or minute areas of regression that suggest malignancy. Dome-shaped, pigmented lesions with uniform speckling over the surface are usually benign dermal nevi . A flat, dark macule with a uniform, netlike pattern is usually a lentigo. Lentigines with netlike patterns are most often found on the trunk.

COMMON MOLES
Nevi may be classified as acquired or congenital, but clinical classification is based on appearance.
Classification.
Common moles are subdivided into three types: junctional, compound, and dermal, based on the location of the nevus cells in the skin. The three types represent sequential developmental stages in the life history of a mole. During childhood, nevi begin as flat junction nevi in which the nevus cells are located at the dermoepidermal junction. They evolve into compound nevi when some of the cells migrate into the dermis. Migration of all of the nevus cells into the dermis results in a dermal nevus. Dermal nevi usually form only in adults, but this evolution does not consistently occur. Nevi with cells confined to the dermoepidermal junction area tend to be flat, whereas those with cells confined to the dermis are usually elevated.