Blue nevushttps://en.wikipedia.org/wiki/Blue_nevus
Blue nevus is a type of colored nevus, typically a single well-demarcated blue or black nodule. The blue color of the nevus is caused by the pigmentary cells being deep in the skin.

A biopsy is sometimes performed, or the whole lesion surgically removed. The clinical outcome is generally good and there is a small chance of cancerous transformation. Differential diagnosis includes dermatofibroma and melanoma.

  • Because the nevus cells are deeply present, it appears blue.
  • Atypical example ― Blue nevus usually has a symmetrical shape. Basal cell carcinoma and melanoma should be differentiated in such cases