The causes of breast swelling and pain include physiological causes and pathological factors such as cervical spondylosis, mastitis and breast cancer. 1. Physiological reasons: when the chest muscles are in a posture for a long time, the muscles are easy to strain, then the phenomenon of chest swelling and pain can occur after bending over. 2. Cervical spondylosis: If the patient has cervical spondylosis, then lowering the head can lead to further pressure on the sympathetic nerves, and breast pain can also occur at this time. 3. Mastitis: when the breast is infected by bacteria and other microorganisms, the bacteria will damage the breast, so the breast will be painful when the head bends down. 4. Breast cancer: due to the massive proliferation of tumor cells, the tumor cells will compress the peripheral nerves, and bending down will lead to increased compression of the tumor on the nerves, so there is swelling and pain. Finally, if there is a phenomenon of breast swelling and pain when you bend down, please go to the hospital for examination in time.