The relationship between breasts and periods is related to the body’s hormone levels. Hormones in the female body mainly include estrogen, progesterone and lactogen. Because of the effects of estrogen in the body, it leads to epithelial hyperplasia accumulating 2-3 layers of cells during the 3rd-7th day of the menstrual cycle, thus making the inner lumen of the breast cells invisible. During the 15-20 days of the menstrual cycle, the breast tissue enters the luteal differentiation phase with the onset of ovulation and increased levels of progesterone and prolactin. During this period, due to the action of progesterone hormone, the glycogen content in the breast increases and is secreted into the stroma, vacuoles and air sacs appear in the basal cells, but there is no proliferation, the base is lax, and the basement membrane is not visible. To summarize, it can be concluded from the physiological changes in the breasts that when the menstrual period is in the 21-27 day period, the breasts may be edematous and congested, making the breasts larger and harder with small nodules. During this period, most women may feel swelling, discomfort or slight pain and pressure in the breasts.