Why does milk discharge from my nipples without being pregnant?

Q: What could be the cause for a 20 years old woman to discharge milk from her nipples without being pregnant?

A:There can be various causes for milk discharge from the nipples without being pregnant. High serum prolactin levels due to various causes like stress; drugs, low thyroid hormones (which causes increased TSH), excessive handling of nipples, tumours of the pituitary glands etc can cause milk discharge in a woman not pregnant. This condition has to be investigated.