Milk leaking from your breasts when you’re not pregnant or breastfeeding is called galactorrhea, and it’s more common than most people realize. It can happen to anyone, including men and children, though it occurs most often in women. The cause is almost always an excess of prolactin, the hormone that triggers milk production, and the reason your prolactin is elevated usually falls into a handful of identifiable categories.
How Prolactin Triggers Milk Production
Prolactin is produced by the pituitary gland, a small structure at the base of your brain. Under normal circumstances, your brain keeps prolactin in check by releasing dopamine, which acts as a brake on prolactin secretion. When that brake weakens or something else pushes prolactin levels up, your body interprets the signal the same way it would during breastfeeding: it starts making milk.
Normal prolactin levels range from about 2.6 to 13.1 ng/mL in men and 3.3 to 26.7 ng/mL in premenopausal women. Anything above those ranges can potentially cause breast discharge, though symptoms vary from person to person. If you stopped breastfeeding more than a year ago and milk is still coming out, that’s also considered galactorrhea rather than residual lactation.
Medications Are the Most Overlooked Cause
A surprisingly long list of common medications can raise prolactin levels enough to cause milky discharge. Many of them work by interfering with dopamine, which removes the natural brake on prolactin production. If you started a new medication in the weeks or months before noticing the discharge, that’s worth flagging with your doctor.
The most frequent culprits include:
- Antipsychotic medications (both older and newer types), which are among the most common drug-related causes
- Antidepressants, particularly SSRIs like sertraline, fluoxetine, and paroxetine, as well as some tricyclic antidepressants
- Birth control pills and other estrogen-containing medications
- Blood pressure medications like verapamil
- Anti-nausea drugs commonly used for acid reflux or motility problems
- Opioid pain medications
- Acid reflux medications in the H2 blocker category
If a medication is the cause, the discharge typically resolves after switching to an alternative or adjusting the dose, though that decision should involve whichever provider prescribed the medication.
Pituitary Tumors Sound Scarier Than They Are
The single most common medical cause of galactorrhea is a prolactinoma, a benign tumor on the pituitary gland that churns out excess prolactin. These tumors are not cancerous. Most are microadenomas, meaning they’re smaller than 10 mm, and they stay confined to the pituitary area without pressing on surrounding structures.
Prolactin levels tend to correlate with tumor size. Microadenomas typically produce prolactin levels below 200 ng/mL, while larger tumors (macroadenomas over 1 cm) can push levels into the hundreds or thousands. Smaller tumors often cause only hormonal symptoms: milky discharge, irregular or missed periods, reduced sex drive, or difficulty getting pregnant. Larger tumors may press on nearby structures, causing headaches or changes in peripheral vision.
In men, prolactinomas often go undetected longer because the early symptoms, like decreased libido and erectile dysfunction, tend to be attributed to other causes. By the time milk production or vision changes appear, the tumor may be larger.
Prolactinomas are highly treatable. Most respond well to medication that mimics dopamine, shrinking the tumor and bringing prolactin back to normal. Surgery is rarely needed.
Thyroid Problems Can Be the Hidden Trigger
An underactive thyroid is a frequently missed cause of milky breast discharge. The connection is indirect but well established. When your thyroid hormone levels drop, your brain compensates by releasing more thyrotropin-releasing hormone (TRH). That same TRH stimulates your pituitary gland to produce extra prolactin, which can be enough to trigger milk production.
The good news is that this form of galactorrhea resolves once the thyroid issue is treated. When thyroid hormone levels return to normal with standard thyroid medication, prolactin typically drops back into the normal range and the discharge stops. Even subclinical hypothyroidism, a milder form that doesn’t always cause obvious thyroid symptoms, has been linked to elevated prolactin and galactorrhea.
Breast Stimulation and Other Physical Causes
Sometimes the answer is mechanical. Repeated nipple stimulation, whether from sexual activity, friction from clothing, or frequent breast self-exams, can trigger prolactin release and produce a small amount of milky discharge. Chest wall injuries, surgeries, and even conditions like shingles affecting the chest area have been associated with elevated prolactin and galactorrhea. Kidney failure can also cause elevated prolactin because the kidneys are responsible for clearing prolactin from the bloodstream.
Not All Discharge Is Milk
The color and consistency of what’s coming from your nipple matters a great deal. True galactorrhea produces white, milky fluid, sometimes from both breasts and multiple ducts. Other types of discharge point to different causes entirely.
- Clear or faintly yellow (serous): often caused by benign growths inside the milk ducts called intraductal papillomas, or by fibrocystic breast changes
- Pink-tinged or bloody: in a study of 370 patients with this type of discharge, about 50% had intraductal papillomas, 31% had fibrocystic disease, and roughly 14% had breast cancer
- Green or dark: typically associated with duct ectasia, a benign condition where milk ducts widen and walls thicken
Discharge that is unilateral (from one breast only), comes from a single duct, is persistent, or is bloody deserves prompt evaluation. The risk of cancer increases when discharge is accompanied by a lump, skin changes like dimpling or puckering, nipple inversion, or swelling near the armpit or collarbone. These signs are more concerning in people over 50. Milky discharge from both breasts, by contrast, has no meaningful association with breast cancer, so mammography isn’t typically needed for galactorrhea alone.
What Testing Looks Like
If you see a doctor about milky discharge, the workup is usually straightforward. The first step is a pregnancy test, since that’s the most common reason for breast milk production overall. After that, a blood draw checks your prolactin level and thyroid function. Kidney function may also be tested.
If your prolactin comes back elevated (generally above 20 ng/mL), or if you’re also experiencing missed periods, headaches, or vision changes, the next step is typically an MRI of the brain to look at the pituitary gland. This is the standard way to identify or rule out a prolactinoma. The MRI is focused specifically on the pituitary region and is a quick, non-invasive scan.
In many cases, especially when the discharge is small in volume and prolactin is only mildly elevated, no serious cause is found. Idiopathic galactorrhea, meaning no identifiable cause, is a common diagnosis. It’s not dangerous, though it can be annoying. It often resolves on its own over time.