There are two reasons for the swelling and pain of both breasts: First, physiological, that is, normal, swelling and tenderness before menstruation, pregnancy or adolescent girls during puberty, which is related to the change of hormone levels. Second, pathologic, that is, abnormal, most often seen in breast hyperplasia, also known as cystic hyperplasia of the breast, most often seen in middle-aged women, is a chronic disease, related to the imbalance of the ratio of estrogen, progesterone, manifested as one or both sides of the breast distension and pain, lump, distension and pain before menstruation is obvious, after menstruation to reduce, after menopause, the above symptoms can be relieved most of the time. Although it is a benign lesion, it has the probability of becoming cancerous and requires regular breast ultrasound examination. Mastitis and breast tumor can also cause breast swelling and pain, mostly unilateral. Mastitis is mostly seen about one month after giving birth, which is characterized by redness, swelling, heat and pain on the affected side of the breast. Breast tumors, such as breast fibroma and malignant breast tumor, are also mostly unilateral. It is recommended to go to the general surgery department or breast surgery department of the hospital for a clear diagnosis.