Most sebaceous cysts on the back are caused by blockage of the sebaceous ducts on the back, resulting in the secretion of the sebaceous glands not being discharged from the body in a timely manner, and the walls of the sebaceous glands gradually increasing in size and secretion. If the infection is secondary, localized redness, swelling and pain will occur, which will be treated with local anti-inflammatory creams. Of course, a hard pack on the back can also be caused by other reasons. A lipoma on the back can also manifest itself as a hard pack when touched, and in some special cases, malignant tumors or other tumors that have metastasized, which need to be further diagnosed in the hospital.