Breast swelling and pain before each menstrual period may be due to breast enlargement, acute mastitis or excessive estrogen secretion. 1. Breast enlargement: If you suffer from breast enlargement, before menstruation, due to abnormally high levels of hormones in the body, it will result in a significant increase in the symptoms of breast enlargement, manifested as swelling and pain in the breasts, and some of the symptoms are more serious, and the pain is alleviated after the menstrual period. 2. Acute mastitis: occurs due to milk stagnation, leading to bacterial invasion, often occurring in the postpartum 3~4 weeks, clinical manifestations of breast pain, local redness and swelling, with the progression of inflammation can be accompanied by high fever, accelerated pulse and other systemic manifestations. 3. Excessive secretion of estrogen: Before menstruation, estrogen will reach the second peak, due to the elevated level of estrogen, it will promote the proliferation of mammary ducts, so it will be manifested as breast swelling and pain before menstruation, which is a normal phenomenon, and the symptom will be gradually reduced after the end of the vacation. If breast swelling and pain occurs before menstruation, it is recommended to consult a doctor in time, except for the possibility of pathology, and follow the doctor’s instructions to receive treatment.