A nevus is a common skin lesion. Any pigmented lesion must be accurately diagnosed. Nevi are more correctly called melanocytic nevi, as they are caused by a proliferation of pigmented cells or melanocytes. If they are brown or black they can also be called pigmented nevi. They are by nature benign, but can give rise to a malign melanoma. Nevi can be flat or raised, and vary in colour from skin-pink tones to dark brown or black. They are usually round or oval shaped, but sometimes assume other unusual shapes, and can vary in size from a couple of millimetres to several centimetres in diameter. One or more nevi may be present at birth (congenital nevus) but they usually appear in childhood or adult life (acquired nevus). They are classified according to the histological location of the nevus cells as follows: junctional (located between epidermis and dermis), intradermal (located in the dermis), compound (located both between epidermis and dermis, and in the dermis) and combination (nevi are present at different depths simultaneously). Dermopathologists have also given some of them the names of those who first described them – for example, the congenital nevus of Ota, and the acquired nevi of Miescher, Unna, Sutton, Meyerson etc. Nevi can usually be surgically treated with the removal of a lozenge-shaped piece of skin. Some of them (e.g. nevi of Miescher and Unna) can be removed by shaving parallel to the skin, leaving a wound that heals spontaneously.