The ability to express breast milk without being pregnant can be caused by factors such as hyperprolactinemia, medication, or breast disease. 1. Hyperprolactinemia. Hyperprolactinemia caused by hypothalamic disease, pituitary disease, primary hypothyroidism, idiopathic hyperprolactinemia and other diseases with menstrual disorders and infertility, breast milk spillage, headache, blurred vision and visual disturbances, and changes in sexual function as clinical symptoms. 2. Drug factors. Long-term use of oral contraceptives may also lead to increased levels of prolactin in the body, resulting in non-pregnancy lactation. 3. Breast disease. When a woman suffers from mastitis, her breast follicles and ducts will erode, degenerate and necrose to form abscesses, which will be discharged through the breast ducts, resulting in non-pregnant pus overflow from the breasts. In addition, after suffering from breast cancer, the cancerous tissue invades the breast ducts, resulting in capillary hemorrhage, there will also be the symptom of being able to squeeze out breast milk without pregnancy, usually bloody nipple overflow. There are many reasons why you can express breast milk without pregnancy, so it is recommended that you consult a doctor in time to clarify the cause and then treat it.