Children’s neck black can not be washed off may be related to birthmarks, hyperpigmentation, acanthosis nigricans and so on. 1. Hyperpigmentation: Normal skin color is mainly determined by the content of melanin in the skin. When the sun, chemical stimulation and other factors lead to excessive production of pigment, it can lead to deepening of skin color pigmentation, which may lead to children’s neck black can not be washed off. 2. Acanthosis nigricans: Acanthosis nigricans is a rare skin disease, which may be related to endocrine disorders, sympathetic nervous disorders, disease factors, heredity, obesity and other factors. It is mainly characterized by excessive skin pigmentation and velvety thickening, which may also lead to a child’s neck black wash away. When there is a child’s neck black can not be washed off, it is recommended to go to the hospital in time for examination, and under the guidance of the doctor to actively accept the treatment, to avoid delaying the condition.