Common causes of a hard lump under the ribs include lipoma, muscle strain, and costochondritis. 1. Lipoma: It is a slow-growing fatty lump most commonly found between the skin and the underlying muscle. Lipoma is a non-cancerous lump formed due to the overgrowth of fat cells, and it can grow in any part of the body. Most lipomas do not cause any pain or other symptoms. 2. Muscle strain: Muscle strain is mainly characterized by hardness or pain in the injured area, swelling, muscle tension, hardness, spasm, and hard lumps that can be felt by touching with hands. 3. Costochondritis: related to strain and trauma, inflammation of the muscle fiber tissue in the attachment part of the pectoralis major muscle, edema and thickening of the cartilage of the articular surface of the thoracic ribs, and aseptic inflammation. Acute onset may feel chest tingling, throbbing pain or soreness, chronic onset may appear swollen and bulging at the rib cartilage, but the skin is not red, and the pain is obvious at the outer edge of the sternum when pressed. There may be other causes such as osteoma, etc. It is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy.