My breasts have both been leaking milk for years it is pure white, never been pregnant and only 22 starting to get worried. what could be causing this?

Need blood test: You need to have a blood test done called Prolactin. This is a hormone that can be secreted by benign tumors in the brain called Prolactinomas or pituitary microadenomas. Leaking milk is called galactorrhea. Certain medications can also cause this. Schedule a visit for evaluation and testing

Elevated prolactin: What you describe is usually due to an elevated prolactin level. That can be caused by a number of issues including some medications, exercise, and / or by a prolactin secreting tumor.You should see your doctor for an exam and probably some lab work (blood test) to determine a reason for your milk production.