A bag in the middle of the chest may be caused by folliculitis, lipoma, bone tumor and other factors. 1. Folliculitis: this disease may be related to Staphylococcus aureus infection, due to inflammation stimulation, the skin will appear red, swollen, hot, painful and other symptoms, a bag may appear in the middle of the chest. 2. Lipoma: this disease may be related to heredity, abnormal fat metabolism and other factors, when the disease is in the middle of the chest, it may lead to the appearance of small painless lumps under the skin, which may move when pushed. 3. Bone tumors: the disease may be related to genetic variation, the sternum with bone tumors will lead to sternal pain, lumps, dysfunction and other symptoms, the late stage may also cause anemia, cachexia, low fever. There are many factors that lead to a bag in the middle of the chest, and it is recommended that patients seek timely treatment.