Black neck is not psoriasis, but a rare skin condition called acanthosis nigricans. 1. Acanthosis nigricans is a skin disorder characterized by increased skin pigmentation, velvety thickening, hyperkeratosis, and warty proliferation. The lesions tend to occur in skin folds, such as the armpits, groin, genitals, neck, popliteal fossa, and elbow sockets. 2. Typical symptoms of the disease are deepening of skin color, dryness and roughness, and elevated papillae. The cause of the disease is not clear, may be related to obesity, heredity. Common therapeutic drugs include Calcipotriol, vitamin D3 analogs, salicylic acid, and retinoic acid cream. 3. The discovery of acanthosis nigricans needs to be checked for the presence of visceral tumors or complications of diabetes mellitus. Obese people need to lose weight and eat less greasy and spicy food. If you find the above symptoms, you should consult a doctor in time and should not use medicine without authorization.