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Nipple discharge is rarely the sign of anything serious provided there are no other symptoms such as a lump, permanent pulling in of the nipple or severe pain. There are several ducts coming to the surface on each nipple. Discharge frequently comes from several ducts at the same time - can be due to duct ectasia.
Intermittent discharge which is clear, yellow, creamy, bluish, greenish or brown is considered normal. Red blood can also mean papilloren in a duct - which is benign. It is only if the discharge is red blood coloured that it needs further investigation by your doctor. The best way of distinguishing red from brown discharge is to dab a little onto a white tissue and look at it under a good light.