A lump on the back against the right shoulder may be caused by lipoma, sebaceous cyst, boil and other factors. 1. Lipoma: It is a slow-growing fat mass, usually located between the skin and muscle, commonly found in the neck, back, abdomen, limbs, etc. It can be single or multiple, and the mass is movable, soft and painless. It can lead to a bag at the back and right shoulder. 2. Sebaceous cysts: the sebaceous glands secretion of the cortex in the gland and the accumulation of the result, most common in the adolescent population, occurring in the head and face, neck and back, buttocks skin. The main manifestations are cysts and pain. If accompanied by infection, it can cause redness and pus in the cysts. It can also cause a bag to grow on the back against the right shoulder. 3. Boils: purulent inflammation of the deep part of the hair follicle and the surrounding tissues, occurring on the head and face, neck and buttocks. The main manifestation is a red, painful lump, after a few days, the head of the boil can appear yellowish-white dotted pus spots, and pus or pus and blood can flow out after shedding. It can also lead to a bump on the back against the right shoulder. There are many causes of a bump on the right shoulder of the back, so it should be taken seriously, consult a doctor in time to identify the cause of the disease, and follow the doctor’s advice for further treatment or therapy.