Bleeding from the breast is usually caused by diseases such as mastitis, breast hyperplasia or breast cancer. 1. Mastitis: Usually, when the milk ducts are blocked and the milk is retained in the ducts, it leads to infection. Milk contains a lot of nutrients and is a better medium for growth and reproduction. Among them, Staphylococcus aureus is the most common, which can cause mastitis through reverse invasion within the lymphatic or milk ducts. Excessive accumulation of breast milk can lead to bleeding on the surface of the breast if the breast is compressed. 2. Mammary gland hyperplasia: Mammary gland hyperplasia is usually caused by endocrine disorders and high estrogen. The accumulation of fluid caused by the proliferation and shedding of the epithelium of the breast follicles may cause breast enlargement, which may lead to nipple extrusion of blood and water. 3. Breast Cancer: Breast cancer is usually a lump to advanced stages will appear nipple ulceration, nipple inversion and other symptoms, which will lead to breast bleeding. Breast bleeding may also be due to other reasons, it is recommended that patients with breast bleeding go to the hospital for timely examination and reasonable treatment under the guidance of doctors.