Blue nevus is also called benign mesenchymal melanoma, blue nevus, pheochromocytoma, melanoma, benign mesenchymal melanoma and so on. It is a benign tumor composed of blue nevus cells. There are three types of blue nevus: common blue nevus, cellular blue nevus and mixed blue nevus. The common blue nevus lesions are large, often progressive, and occasionally benign lymph node metastasis. It can occur at birth or after birth. In addition to common skin, it can also occur in oral mucosa, cervix, vagina, spermatic cord, prostate and lymph nodes. Blue nevus can become malignant.