Breast pain and menstruation can be caused by changes in hormone levels, breast enlargement, non-lactating mastitis, and other diseases such as breast cancer. 1. Changes in hormone levels: Hormone levels change when a woman is menstruating, stimulating breast ducts to proliferate and breast follicles to develop, and women may experience breast pain. This is a normal physiological manifestation and will usually return to normal after menstruation. 2. Mammary hyperplasia: Mammary hyperplasia is considered to be caused by endocrine dysfunction, and patients will have breast pain, breast lumps, nipple overflow and other manifestations. If breast enlargement occurs during menstruation, it will be manifested as breast swelling and pain and menstruation. 3. Non-lactating mastitis: The cause of non-lactating mastitis is not yet clear, and it is considered to be related to bacterial infection, nipple acuity, and dilated mammary ducts. The patient may show redness, swelling, heat and pain in the breast, breast lumps, etc. Therefore, the patient may have breast swelling and pain and menstruation during the menstrual period. 4. Other: Women who have breast swelling and pain with menstruation are also considered to have breast cancer, breast trauma, cardiothoracic diseases, and breast engorgement after sexual intercourse. It is recommended that women who have breast swelling and pain and menstruation need to consult a doctor in time, if it is caused by hormonal changes in the body, usually do not need treatment. If it is caused by a disease, it is necessary to take appropriate measures to treat the cause of the disease.