Different causes of breast nodules are different, mainly related to bacterial infection, sex hormones, heredity, obesity, age and so on. 1. Acute mastitis: mainly caused by staphylococcus aureus invasion and infection after milk stasis of primiparous women and nipple rupture, breast abscess can be manifested as nodules. 2. Breast cystic hyperplasia: estrogen and progesterone imbalance, leading to overgrowth of part of the parenchyma, appearing as breast lumps, which are manifested as breast nodules in ultrasound and other imaging examinations. 3. Benign breast tumors: such as breast fibroma, associated with abnormal increase in sensitivity of fibroblasts to estrogen, local fibrous tissue hyperplasia produces nodules. 4. Breast malignant tumor: the development of breast cancer is directly related to estrogen, early menarche, late menopause, late first pregnancy, infertility, etc. It is also related to age, heredity, obesity, diet and environment. Breast nodules may be caused by benign diseases or malignant diseases, and patients are advised to consult the doctor in time for further examination and treatment as prescribed by the doctor.