Hard lumps in the middle triangle of the chest may be caused by sternal fracture, skin disease, allergy, enlarged lymph nodes under the skin and other factors. 1. Sternum fracture: when sternum fracture occurs due to trauma or other factors, the sternum may be deformed, and the fracture end may protrude to the surface of the skin, and a hard lump can be touched at the chest. 2. Skin disease: when lipoma, subcutaneous fibroma, sebaceous cyst and other diseases appear in the middle triangle of chest, there may be local swelling and hard lumps. 3. Allergy: the skin at the chest touches the allergens or the poor material of the clothes, which can lead to the allergic manifestation of the skin at the chest, and the localized pimples can occur, and in the long run, repeated friction, the skin at the chest can be manifested as hard lumps. 4. Enlarged subcutaneous lymph nodes: Enlarged subcutaneous lymph nodes in the chest triangle may appear hard lumps, and pressure pain may appear when the inflammation is serious, and we should be alert to the factors of metastatic lymph node enlargement of lung cancer or breast cancer. When there are hard lumps in the middle triangle of the chest, you should consult a doctor in time and take active treatment under the guidance of a specialized doctor, which will help to relieve the uncomfortable symptoms as soon as possible.