Hard bumps on the shoulder are considered for several reasons. First, the most common cause is sebaceous cysts, where the sebaceous glands secrete normal sweat, but the small ducts of the sebaceous glands are blocked by sweat or surrounding tissues, causing the sweat to fail to drain and gradually expand. This results in the formation of sebaceous cysts, which are usually hard and not painful. When infected, it can cause pain. Secondly, tendon sheath cysts are caused by chronic friction between the tendons and tendon sheaths around the shoulder, which causes fluid accumulation and outward expansion of the tendon sheaths, thus causing tendon sheath cysts.