Pain in the left breast is commonly caused by the following reasons: First, mastopexy: when mastopexy is more serious, there will be obvious pain, especially before menstruation, the symptoms will be more obvious, with the end of the menstrual period, the symptoms can gradually reduce. You can go to the hospital to check the ultrasound, and other imaging tests for clarification. If the disease, you can take oral medication for treatment, commonly used are breast fetish elimination or prolotherapy pills. Secondly, trauma to the breast: related to bump or too strenuous exercise. Third, the breast growth has benign masses: such as fibroids, you can check the breast ultrasound or mammogram examination to clarify. Fourth, malignant breast tumor: such as breast cancer, need to perform breast ultrasound, mammography, and if suspicious tissue is found, need to perform puncture biopsy to clarify the nature.