Water seepage from surgical incision of breast cancer is mostly caused by fat liquefaction, secondary bacterial infection or subcutaneous fluid accumulation. 1. Fat liquefaction: during surgery, breast cancer patients may affect the surrounding fat, which may cause fat liquefaction, and then the symptom of oozing from surgical incision may appear. 2. Secondary bacterial infection: if breast cancer patients do not take good care of themselves after the surgery, secondary bacterial infection can occur, leading to pus in the area, and the symptom of oozing from the surgical incision can also occur, accompanied by obvious redness, swelling and pain. 3. Subcutaneous effusion: after breast cancer patients choose surgery, blood or tissue exudate can appear in the wound causing subcutaneous effusion, which can also lead to the existence of the above symptoms. Patients with breast cancer surgical incision oozing should go to the hospital for consultation in time to clarify the specific cause.