The back of the neck is black in the following cases: 1, pseudo acanthosis nigricans: pseudo acanthosis nigricans is mainly related to obesity, obesity will lead to the neck, armpits, groin and other parts of the color is dark, weight if controlled, the color will also gradually subside. The rash may be improved by controlling the diet, exercising in moderation and reducing the weight. 2.Black degeneration disease: red rashes will appear locally in black degeneration disease, mainly red rashes in the early stage, while pigmentation will gradually appear in the late stage. The treatment of melanosis is mainly vitamin C, vitamin E and pigment reduction treatment, can be used externally Qianbai hydroquinone cream, once a night. 3, due to sun exposure: sun exposure will also lead to local melanin increase, appear deepening color and so on.