The causes of breast cancer are as follows: 1) early menarche, age >12; late menopause, age >55; 2) late marriage, late childbearing, no pregnancy, no breastfeeding; 3) the incidence of breast cancer is related to age, the incidence of breast cancer is low at the age of 0-24, the incidence rate increases after the age of 25, the incidence rate is at the age of 50-55. The incidence rate of breast cancer is low from 0 to 24 years old, increases after 25 years old, and decreases gradually after 55 years old. It is recommended that women should have regular checkups for breast lumps and annual comprehensive physical examination in hospital, mammogram, breast and armpit ultrasound and breast cancer tumor markers if necessary.