There are several reasons for breast swelling and pain: First, due to growth and development, both men and women have varying degrees of breast swelling and pain during development, which is a normal physiological phenomenon. Second, the female body before the onset of menstruation estrogen levels rise, estrogen can stimulate the breast tissue, resulting in hyperplastic swelling and pain in the breast, after the menstruation body estrogen levels return to normal, the pain can disappear. Third, breast hyperplasia, abnormally high estrogen levels in the body, constantly stimulating the breast gland, resulting in abnormal hyperplasia of the breast tissue, resulting in nipple or breast pain. Fourth, breast nodules or breast cysts, due to the increasing size of the swelling, pressure on the nerves around the breast tissue appears compressive pain. Fifth, early pregnancy hormonal stimulation of breast hyperplasia, the breast will have a certain amount of swelling and pain is normal. Sixth, breastfeeding milk accumulation formed acute mastitis, appearing breast swelling and pain discomfort. Seventh, malignant tumors of the breast, the tumor can compress the peripheral nerves appear pain. Eighth, endocrine disorders, resulting in imbalance of hormone secretion in the body appears breast swelling and pain.