A hard lump under the skin of the stomach is considered to be a lipoma, sebaceous cyst, or boil. Boils can disappear on their own, while lipomas and sebaceous cysts will not disappear on their own. 1. Lipoma: Lipoma is a kind of soft tissue benign tumor, mainly manifested as subcutaneous confined lumps, may be one or more, lipoma generally will not disappear on its own, for the smaller lipoma generally do not need special treatment, if the volume is relatively large can be surgically removed. 2. Sebaceous cysts: commonly known as “chalk tumors”, its formation and sebaceous stagnation has a relationship, is the sebaceous gland ducts in the skin is blocked, resulting in the gradual accumulation of sebum formation of retention cysts, this kind of cysts will not disappear on their own, and need to be surgically removed. 3. Boils: acute suppurative inflammation of the hair follicles and the deep surrounding tissues of the hair follicles, most of which are caused by Staphylococcus aureus infections, generally can be broken and healed on their own, do not need any special treatment to disappear on their own, and if the condition is more serious, surgery is required to incise and drain. There may be other reasons (such as dermatofibroma), it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, give targeted treatment or treatment.