Hidden pain in the left breast may be caused by breast hyperplasia, mastitis, breast fibroma and other reasons. 1. Breast hyperplasia: If you have a vague pain in your left breast and a hard lump in the breast, you may be suffering from breast hyperplasia. The pain will be more intense when menstruation is approaching and will be relieved after menstruation is over. 2. Mastitis: If the left breast is red, hot, and painful, it may be mastitis, so you can go to the hospital and take medication to relieve the inflammation; if it is a breastfeeding woman’s breast milk is stagnant and causes mastitis, you need to empty the stagnant milk in time. 3. Breast Fibroid: Breast fibroid can also cause pain in the left breast, the pain is not obvious, the lump increases slowly. At the same time, you should also consider the possibility of breast cancer when there is pain in the breast; you should also consider the possibility of heart disease and stomach disease when there is pain in the left breast. There are many possible causes of pain in the left breast, it is recommended to go to a regular hospital, under the guidance of the doctor to clarify the diagnosis and standardized treatment.