The swelling of both breasts that usually occurs during breastfeeding may be associated with increased milk secretion or poor drainage. 1. Increased secretion: Breastfeeding women need to maintain a normal intake of breast milk for the fetus, but when the fetus sucks on the nipple, it stimulates changes in the body’s hormone regulation axis, leading to the release of prolactin. Therefore, it will further increase the secretion of milk. If the milk in the breast is not discharged in time, there will be a feeling of swelling and pain. 2. Poor discharge: The swelling and pain on both sides of the breast during breastfeeding may be due to poor discharge of milk. As the milk secreted by the breasts cannot be emptied in time, the milk ducts are blocked, and then the mammary glands dilate and compress the milk ducts, which affects the normal discharge of milk, and thus the feeling of breast swelling and pain will occur. At the same time, the breast swelling when breastfeeding also need to exclude breast diseases such as breast hyperplasia, mastitis, breast cancer and so on. Most of the swelling of both breasts while breastfeeding is normal, usually due to excessive milk secretion or poor discharge, but also need to exclude the possibility of mammary gland diseases. If the breast swelling and pain cannot be relieved for a long time, it is recommended to consult a regular hospital in time and standardize the treatment under the guidance of the doctor.