Patient: Description of the condition (onset time, main symptoms, hospital visited, etc.): 18-month-old male baby, 2 months ago found a faint vertical line in the middle nail of the left hand, running through the entire nail, initially the root of the finger is darker, more and more faint upwards, thought it was scratched by the pencil not care. Recently, I found that the black line had become thicker, about 1mm thick, and the top and bottom were as thick. There is no other discomfort and I have not been to the hospital. Is it a nail nevus as described on the internet, how should it be treated, and what are the chances of lesions? No 1. Is it a nail nevus? 2. What is the chance of malignancy? 3. How should I treat it, and can your hospital do so? What are the clinic hours? Zhou Jing, Department of Pediatric Dermatology, Shanghai Children’s Hospital: From your description, it looks like a nail nevus. There are no exact statistics on the chance of malignant transformation, but it is a kind of mole that is more prone to malignant transformation. A nail nevus grows at a young age and stabilizes in adulthood. If there is sudden deepening or unevenness of the damage, widening more than 6mm, irregular border, etc., pathological examination should be done immediately for active treatment. Patient: Thank you, Dr. Zhou, for your reply. Please tell me “nail nevus grows at a young age and stabilizes in adulthood without further development.” What does this mean? Does it mean that nail moles that develop at a young age will not expand and develop into adults? Zhou Jing, Department of Pediatric Dermatology, Shanghai Children’s Hospital: Yes, this is true for benign nail nevi. The implication is that if it continues to grow into adulthood, this kind of nevus needs to be alerted and treated actively. Patient: Again, Dr. Zhou, if the nevus becomes deeper and wider in the juvenile stage, reaching about 6mm, does it need to be operated? If it does not reach 6mm and the border is clear, can we continue to observe it? Thank you very much for your reply. Zhou Jing, Department of Pediatric Dermatology, Shanghai Children’s Hospital: Yes, it can be understood in this way. However, the rules are dead. If you notice any unusual changes in the nail nevus, such as an inflammatory reaction, you need to come to the doctor for a consultation.