Common causes of a soft mass on the sternum include: lipoma, sebaceous adenoma, sebaceous cyst, etc. 1. Lipoma: it is a kind of soft tissue benign tumor, such as subcutaneous appearance of lipoma at the sternum, which can be manifested as a localized soft mass, usually less than 5cm in diameter, with clear boundary, lobulated or oval, with movable, usually without pain and other discomforts. 2. Sebaceous adenoma: the etiology is not clear, it is often manifested as painless, slow-growing papules, plaques or nodular lesions, and its color is mostly red or yellow, with clear boundary and soft texture. If it appears in the upper part of the sternum, it may appear as a soft mass. 3. Sebaceous cysts: mostly caused by the blockage of sebaceous gland excretory ducts, the chest also exists sebaceous glands, such as blockage may appear sebaceous cysts, generally manifested as round masses, with a certain degree of elasticity higher than the skin surface, the surface is smooth, the texture is soft. There are many other reasons why there is a soft bag on the sternum, you need to consult a doctor in time and follow the doctor’s instructions to avoid aggravation of the condition.