Constant itching on the back is usually caused by dry skin, pruritus, eczema, etc. 1. Dry skin: When the indoor air is dry, the temperature drops, the body’s skin barrier function decreases, the small blood vessels in the skin and subcutaneous contraction, and the secretion and excretion of sebaceous glands and sweat glands are also reduced, which leads to dry skin and cracks, making people feel itchy. 2. Pruritus: As sebum secretion decreases in old age, it causes itchy skin, renal failure, heart failure, hypertension, diabetes and other internal diseases. 3. Eczema: as the back long eczema will appear red spots, papules, vesicles, oozing and other polymorphic rashes, accompanied by a certain degree of itching. The back is always itchy may also be due to folliculitis, chronic diseases, etc., patients with serious symptoms, should promptly go to the hospital dermatology under the diagnosis of the doctor standardized treatment.