Children’s neck black black can not be washed off may be related to pigmentation, ultraviolet radiation, benign acanthosis nigricans and so on. 1. pigmentation: neck black can not wash off may be related to the friction at the neck, caused by melanin precipitation, so that the phenomenon of not washing off. 2. Ultraviolet radiation: children do not do a good job of sun protection when they are active in the sun, and their necks will be exposed to ultraviolet tanning. 3. Benign acanthosis nigricans: it may also be associated with benign acanthosis nigricans, which appears as pigmented skin lesions. Children’s neck black wash may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor’s treatment.