There are several reasons for breast swelling during menstruation: 1, estrogen and progesterone changes fluctuate greatly: breast swelling during menstruation is due to estrogen and progesterone in women during menstruation, changes fluctuate greatly caused. Breasts are more sensitive to changes in estrogen and progesterone levels, and when this endocrine fluctuation is large, it affects the function of the mammary glands and is the main physiological factor that causes breast swelling and pain during menstruation. If the symptoms of breast swelling and pain during menstruation are mild, usually belongs to the physiological breast swelling and pain, may not need special treatment. 2, physical decline: breast swelling and pain is also related to the decline in physical condition, because during menstruation, women are in the state of bleeding, loss of blood, the physical condition is also relatively weak, the primary breast disease, such as breast hyperplasia, cystic lesions of the mammary glands and other diseases to take advantage of the situation, but also aggravate the swelling of the mammary glands. If the breast swelling and pain is more intense, may be the menstrual period of the body is weaker, work pressure is more anxious fire, triggering the liver fire in the middle cross, dampness and heat on the top, manifested as breast swelling and pain aggravation.