The relative risk of breast cancer for women with family history is 4.5 (95% confidence limit 2.09-9.68), and family history of breast cancer is an important risk factor. 2) Reproductive factors 1) The risk of breast cancer is high when menarche is before the age of 12, and the risk of breast cancer decreases by 20% when menarche is delayed by one year. 2) The risk of breast cancer is high when menopause occurs after the age of 55, and the probability of breast cancer increases by 3% for each year of delay. 3) Menstrual cycle Short menstrual cycle increases the risk of breast cancer, otherwise it decreases the risk. 4) Age of the first full-term pregnancy The younger the age, the lower the lifetime risk of cancer. 5) Number of births Women with high number of births are less likely to develop cancer. (6) Breastfeeding history Women who breastfeed normally have less risk of cancer. 3.Estrogens (endogenous and exogenous), androgens, prolactin and other hormones all play a role in promoting the occurrence of breast cancer. 4.Dietary factors 1）High fat and high calorie, ethanol all increase the incidence of cancer. 2) Low fiber, low vitamin and low trace elements also increase the occurrence of cancer. 5.Environmental factors 1) Ionizing radiation The longer the exposure to radiation, the higher the risk, and the younger the age, the higher the risk. 2) Drugs Chemotherapy drugs, birth control pills, drugs that increase lactogen, etc. 3) Women with little physical exercise have a higher risk of cancer. 4) Occupation Beauty industry, chemical industry, drug manufacturing, etc. 6) Other diseases Diabetes and thyroid disease are related to the occurrence of breast cancer.