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.

[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.

[2] It was first studied in 1906 by Tièche, a student of Josef Jadassohn.