Breast tenderness can occur during ovulation. Breast tenderness during ovulation is mainly due to the increase of estrogen secretion in the body and the expansion of the ducts and lobules of the mammary glands, resulting in mild breast tenderness. After the egg is expelled, the hormone level in the body will gradually decrease and the breast pain will be relieved on its own. If the mature egg is discharged, the egg and sperm combine to form a fertilized egg, and the fertilized egg comes to rest in the uterine cavity to form an early pregnancy, the early pregnancy will continue to cause breast tenderness and pain. After the mature egg is discharged, if there is no sperm and egg union, the estrogen level in the body gradually decreases and the breast swelling and pain will ease on its own. When the next menstrual period comes, the hormone levels increase and breast tenderness will occur again.