A blue nevus is a special type of benign mole that is dark blue in color.
A blue nevus is a result of pigment-producing cells (melanocytes) being deeper in the skin than typical brown moles, freckles, and sunspots.
The cause of blue nevi is unknown. Some researchers believe that they are caused by the inability of melanocytes to migrate and reach the upper layers of the skin during embryonic development.
Blue nevi are harmless; no treatment is needed unless they cause pain or bleeding. Otherwise, treatment is mainly for cosmetic reasons.
There are several surgical techniques to remove a blue nevus including a biopsy or a surgical excision.