Pain over the left breast is clinically common in three main diseases: the first common disease is mainly in breastfeeding female patients with acute mastitis caused by a ruptured nipple secondary to bacterial infection due to infant sucking on the nipple. Further ultrasound examination is usually required to rule out the possibility of breast abscess. Treatment is mainly with penicillin G antibiotics and surgical incision and drainage is required if an abscess is formed. The second common disease is cystic hyperplasia of the breast, which is the most common in young and middle-aged women and requires further ultrasound examination of the breast for a clear diagnosis. Relief or cure of clinical symptoms can be obtained by simply eating a light diet, relaxing and de-stressing the liver and Qi. In the third case, breast disease is ruled out and the possibility of intercostal neuritis needs to be alerted. It usually requires oral vitamin medication and even oral NSAIDs for analgesia if necessary.