A blue nevus is a type of coloured mole, typically a single well-defined blue-black bump.

[1][2] The blue colour is caused by the pigment being deep in the skin.

[4] A biopsy is sometimes performed, or the whole lesion surgically removed.

[3] The outcome is generally good but there is a small chance of cancerous transformation.

[3] Blue nevi are more common in females than males.