Yellowish fluid refers to nipple discharge, which may be caused by physiological reasons, breast abscess or breast trauma. 1. Physiological reasons: when a woman is pregnant or breastfeeding, nipple overflow can occur to varying degrees, and at this time the breast can overflow yellowish liquid, which is a normal physiological phenomenon. 2. Breast abscess: When the milk ducts are infected by bacteria, it can lead to pus in the area and induce breast abscess. This disease can cause pus to appear in the breast area, which can also cause the symptom of yellowish fluid in the breast. 3. Breast trauma: when the breast is traumatized by the outside world, it may cause capillary rupture or tissue interstitial fluid overflow, which may also cause the above symptoms, and the patient may also be accompanied by pain and redness and swelling and other manifestations. Breast overflow yellowish fluid may also be caused by intraductal papilloma, cystic hyperplasia of the breast, breast cancer and other diseases, patients should go to the hospital in time to receive treatment.