Pain in the left breast when breathing is associated with mastitis, nodular hyperplasia, and trauma, and pain in the breast area when breathing is associated with acute mastitis. As a result of nipple breakage will lead to local bacterial growth, bacteria will flow up the breast ducts and combine with stagnant milk to form inflammation in the breast area leading to local lump enlargement and compression of the surrounding nerves, and pain will occur in the affected breast when breathing. Due to liver stagnation and qi stagnation in the human body, the change in hormone level before menstruation will lead to edema in the enlarged lump. The pain will occur in the area of the enlarged lump when the human body breathes hard, which is considered to be caused by trauma to the chest.