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Q: I am a 45-year-old female. I recently noticed dark greenish discharge from both breasts. What could be causing this?

A: Unless a woman is making milk and breastfeeding, it can feel very alarming to have discharge from the nipples. Even so, this occurs fairly commonly and there is usually a good explanation.

What can cause a liquid discharge from the breasts? Usually, even if the liquid is colored yellow, greenish, gray, or brown instead of being purely clear or white, the liquid is actually milk that has been made by the breast.

The breasts are programmed to begin making milk during pregnancy. If you have not done so, I would recommend checking a home pregnancy test.

The breasts can also be “tricked” into making milk if your hormone balance imitates what is seen in pregnancy. For example, some women have nipple discharge when they take birth control pills, due to the estrogen and progesterone in the pills.

Another hormone called prolactin signals the breasts to make milk. Prolactin is made in the brain, and many things can shift its level so that milk production gets triggered. Some medications that alter brain chemistry can affect your prolactin level. For example, certain medications used to treat depression and other mental health disorders can raise your prolactin level and trigger a nipple discharge.

A less common cause of an elevated prolactin level is a structural change that occurs in the pituitary gland. The pituitary gland is a pea size structure that sits at the base of the brain. Cells in the pituitary gland sometimes form a benign growth called a prolactinoma.

One amazing thing about milk production and breastfeeding is that a woman’s body has been “programmed” to recognize subtle caressing or stimulation of the nipple as a sign that a baby might be seeking milk. Nipple stimulation triggers a nerve reflex, and this causes hormones to adjust so that milk can be produced. A baby that is suckling on the nipple is the most effective stimulation that can trigger milk production, but massage of the breasts and nipples by the mom or by an intimate partner is sometimes enough. For some women, a bra that causes rubbing because it does not fit well might be enough to stimulate milk production.

If you feel that your milk production is not explained by the above, additional evaluation might include getting a blood test to measure the prolactin level. An elevated prolactin level tends to cause menstrual irregularity as well as unexplained milk production. If the prolactin level is confirmed to be high, an MRI is usually ordered to check for a prolactinoma. Although this sounds like an exotic problem, it is not rare and it is treatable.

If you are having fluid leak from only one breast, not both, or if you see blood in the milk, it is important to consider the possibility that breast cancer might be the cause of your discharge. That said, don’t be overly alarmed: Fewer than 10% of women under age 60 who have a nipple discharge have breast cancer, and breast cancer is almost never the cause when the discharge comes from both breasts.

See All Harvard Articles on Breast Health

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