The dry skin under the mouth is black, may be associated with acanthosis nigricans, atopic dermatitis, seborrheic dermatitis and other factors, the patient can go to the hospital for a detailed examination, to clarify the cause of the disease, and then targeted treatment. 1, acanthosis nigricans: endocrine disorders, obesity, sympathetic nerve disorders, and other factors lead to abnormal changes in the skin, manifested as local skin dryness, roughness and thickening, the surface of the skin there are many small papillae-like elevations, like velvet. Like velvet, the lesion skin is light gray, dark brown, often occurring in the armpits, neck, face, etc., and thus can be seen under the mouth dry peeling black phenomenon. In this regard, can be used externally carbotriol, salicylic acid, vitamin A acid ointment and other drugs, obese people need to reduce weight, endocrine disorders need to correct hormone levels. Daily life should pay attention to the combination of work and rest, maintain an optimistic, calm state of mind, avoid high oil, high sugar food, so as not to aggravate the symptoms; 2, allergic dermatitis: due to contact with allergens lead to an allergic reaction of the organism, there can be a rash, itchy skin and other symptoms, if you scratch the itchy place, it can lead to skin drying and peeling, and long-term lead to melanin deposits, causing the blackening of the performance. In this regard, patients should avoid re-exposure to allergens, under the guidance of the doctor to apply benadryl, loratadine, zinc oxide, vitamin E cream and other drugs to relieve itching, dry skin symptoms; 3, seborrheic dermatitis: due to Malassezia infection, diet and other factors lead to dry skin, itching phenomenon, if you scratch the local area, it may lead to melanin deposition and localized blackening symptoms. If you scratch the area, it may lead to melanin deposition and localized blackening. In this regard, the local application of compound ketoconazole cream, tacrolimus ointment and other drugs, or oral itraconazole and other antifungal drugs.