Thursday, January 10, 2008

Why do moles form on the human body?

The scientific name of mole is Nevus. Medically the moles or nevi are instructive tumors of the skin. The term nevus denotes any congenital lesion of skin. Common acquired nevi are tan-to-brown, uniformly pigmented solid regions of elevated skin with well defined rounded borders. They are usually less than 6mm across. They are formed when single cells which are normally interspersed among basal Keratinocytes are transferred in to round to oval melanocytes called nevus cells that grow in aggregates or nests along the dermal-epidermal junction.

The nuclei of nevi cells are uniform and rounded, contain inconspicuous nucleoli and show little or no mitotic activity. The early developmental stage in nevi are called junctional nevi. When they grow in to underlying dermis as nests or cords of cells they are called compound nevi. When they are still further. Now they are called dermal nevi. Clinically, compound and dermal nevi are often more elevated than junctional nevi. Although nevi are common, their clinical and histological diversity necessitates thorough knowledge of their appearance and natural evolution. Otherwise they become confused with other skin conditions notably malignant melanoma (skin cancer tumor). There are numerous clinical and histological types of nevi. The following are important ones:

1. Congenital nevi: These are present at birth and are called acquired nevi.

2. Spindle and epithelioid cell nevi: They are red-pink nodules and contain large plump cells with pink blue cytoplasm.

3.Blue nevi: These are black blue nodules and are dendritic with heavily pigmented nevus cells.

4. Halo nevi: These are identical to ordinary acquired nevi but provided with lymphocytic infiltration surrounding nevus cells. So they have host immune response.