Women’s mammary glands mature during puberty in response to ovarian hormones, while breast cells undergo physiological proliferation changes due to monthly cyclical changes in body hormone levels and increased body hormone levels during pregnancy. This cell proliferation and division ends at the time of menopause. The development of breast cancer is closely related to many of these reproductive factors. Numerous studies have shown that early age of menarche and late age of menopause are among the major risk factors for the development of breast cancer. Early menarche means early exposure of the breast to estrogen, while late menopause prolongs the exposure of the breast to estrogen, both of which increase the risk of developing breast cancer. According to the experience in the United States, the risk of breast cancer decreases by 20% when the age of menarche is delayed by one year, and the risk of breast cancer is 1.3 times higher when the age of menarche is less than 12 years old than when the age of menarche is greater than 15 years old; domestic studies also show that the risk of breast cancer is 2.2 times higher when the age of menarche is earlier than 13 years old than when the age of menarche is greater than 17 years old. The age of menarche is related to genetics, economic level, nutritional status, geography, etc. Generally speaking, it is earlier in developed countries and later in developing countries, which is positively correlated with the incidence of breast cancer. Late menopause has been shown to be a risk factor for breast cancer. A cohort study in the United States found that the risk of breast cancer for those who had artificial menopause before age 45 was 1/2 that of those who had natural menopause after age 55, and that each year of delay in menopause increased the probability of breast cancer by 3%. Whether early menarche or late menopause, it is actually a woman’s menstrual history that is lengthened. It has been reported that those who have been menstruating for more than 40 years have a 1-fold increased risk of breast cancer compared to those who have been menstruating for less than 30 years. Numerous epidemiological surveys have found that the risk of breast cancer is greater in infertile women than in women who have had children, and the younger the age of a woman’s first normal pregnancy, the less likely she is to develop breast cancer in her lifetime. Since the first full-term pregnancy can lead to a series of changes in the breast epithelium, and the mature epithelium has stronger resistance to mutations, the younger the first full-term pregnancy, the less likely the breast tissue is to be affected by internal and external environmental factors that can lead to mutations. Many studies have shown that late age at first birth and few full-term births are risk factors for breast cancer. Domestic studies have found that the risk of breast cancer increases approximately three times for women who have their first birth after the age of 35 compared to those who have their first birth before the age of 20, and the risk of breast cancer increases for those who have not had a child or have a first full-term birth older than 35 years old; while a high number of births significantly reduces the risk of breast cancer. Clinical studies have found that breastfeeding can reduce the risk of breast cancer, and the total duration of breastfeeding is negatively correlated with the risk of breast cancer, especially for those who breastfeed for a longer period after the first birth. The reason for this is that breastfeeding improves the development of breast tissue and delays ovulation and menstrual reconstruction, and the estrogen level is relatively low during breastfeeding, which is not suitable for breast epithelial cancer.