Pain under the inner breast is considered to be caused by the following factors. First, may be suffering from breast hyperplasia, this disease is usually manifested as a lump or nodule in the breast gland, accompanied by pain, some will appear nipple discharge, and affected by the physiological period, before the onset of menstruation, the pain will be more intense, the lump will become hard, the onset of menstruation after the gradual alleviation of the symptoms. If the emotional fluctuation is too large, or overwork will also lead to aggravation of the condition, this disease needs timely treatment. Second, it may be caused by intercostal neuralgia. Third, if you suffer from inflammation of the costal cartilage, you will also experience pain under the inner side of the breast, and the feeling will be more intense when you are fatigued. Fourth, it may also be caused by mastitis or other diseases, it is best to go to the hospital for further examination and then appropriate treatment.