Blue nevus is a benign tumor from melanocytes, clinically manifested as small blue-black pigmented spots or nodules; its etiology is not yet clear, and it is considered to have certain relationship with heredity, sun exposure and adverse stimuli. 1. Heredity: blue nevus has certain hereditary tendency, especially the existence of hereditary diseases affecting the number of melanocytes, synthesis of melanosomes and tyrosinase synthesis disorders are more likely to be induced. 2. Sun exposure: prolonged sun exposure can lead to deepening of melanin quantity and melanization in cells, thus leading to the appearance of blue nevus, which is more common in plateau areas with strong ultraviolet rays. 3. Undesirable stimulation: prolonged exposure to freezing, chemical corrosion and repeated stimulation of pigmented nevus cells by lasers will easily cause cells to develop atypical hyperplasia or malignant tendency, thus leading to the appearance of blue nevus. When patients have blue nevus, it is recommended to go to the hospital in time to get a clear diagnosis and follow the doctor’s instructions for treatment.