Breast swelling and pain to the back during breastfeeding may be due to acute mastitis or intercostal neuralgia, breast cancer. 1. Acute mastitis: Acute mastitis is an acute purulent infectious inflammation of the mammary gland, which occurs 3⁓4 weeks after delivery in primiparous women, and the patient may have inflammatory manifestations such as chills, high fever, and accelerated pulse. Accompanying the development of the disease may cause the lymph nodes on the side of the disease to swell and cause back involvement pain. 2. Breast stasis with intercostal neuralgia during breastfeeding: then there will be breast swelling and pain with back pain. Intercostal neuralgia is caused by aseptic inflammation of the intercostal nerves, which causes pain along the course of the nerves, and the back nerves may also be stimulated, thus causing back pain. 3. Breast cancer: In breast cancer patients, advanced tumor cells may invade the spine and cause back pain, which may also be accompanied by breast pain, and if it occurs during breastfeeding period, milk stagnation may also lead to breast swelling and pain. In addition, cardiothoracic diseases may also appear in this clinical manifestation, so the clinical manifestation of breast swelling and pain to the back during breastfeeding, we should consult a doctor in time, and follow the doctor’s instructions to standardize the treatment.