Breast nodules are caused by a variety of reasons, such as breast infection, fat necrosis, fibrocystic degeneration and so on. 1. Breast infection: It is most common in breastfeeding women, with the formation of tender nodules in the breast, accompanied by the production of nipple discharge. 2. Fat necrosis: fat necrosis in the breast can be caused by accident or surgical injury, which can precipitate and form nodules. 3. Fibrocystic degeneration: Multifocal small nodules of different sizes are formed in the breast, which are mainly found in women over 35 years old. In addition to the above reasons, there are many other causes of breast nodules, such as genetic factors, exogenous estrogen, trauma, etc. It is recommended that patients with breast nodules go to the hospital as soon as possible to find out the cause of breast nodules, and then follow the doctor’s instructions to receive treatment.