The chance of melanoma occurring in patients under 20 years of age is low, accounting for about 1-4% of the overall melanoma incidence. If pigmented nevi with a diameter of more than 6 mm, irregular edges, uneven pigmentation and asymmetrical morphology appear to expand rapidly or thicken the plaque, surgical excision may be an option to eliminate the hidden danger. For more stable nevi, we can observe and leave them untreated for the time being, because stimulating factors can lead to an increased risk of malignant transformation of pigmented nevi, and we should pay attention to avoiding physical and chemical chronic stimulation and the use of irritating chemical drugs in general.