Yellow water flowing from underarm half a year after breast cancer surgery may be related to fluid accumulation under the skin and local infection. 1. Fluid accumulation under the skin: if there is a lump in the area of yellow water flowing under the armpit, the lump can be pushed, there is a fluctuating sensation inside when pressed, and there is obvious pain, and there is yellow water flowing out after being pressed, it needs to be considered that there is fluid accumulation under the skin. It may be due to the use of drainage tube drainage, the wound site of the liquid tissue is not completely drained. 2. Local infection: if the incision site of breast cancer surgery is in the armpit, if the incision site is infected, it may cause local inflammatory reaction, redness, swelling and pain. In serious cases, it may cause purulent reaction, with symptoms such as yellow water or purulent thick liquid. The yellow water in the armpit half a year after breast cancer surgery should also consider the possibility of recurrence and metastasis, the patient had better consult a doctor in time, do a systematic examination, clarify the cause of the disease and then follow the doctor’s instructions to receive treatment.