Introduction

Nipple discharge is the third most common reason women visit a breast clinic, right after breast pain and breast lumps. It’s a common experience, especially among women of reproductive age. Nearly 80% of women will experience nipple discharge at some point in their lives.¹

While most cases are harmless, the key to proper care lies in figuring out whether the discharge is benign or a sign of something more serious, like a papilloma, a high-risk lesion, or even breast cancer.

In this article, we will go through different aspects of this condition and how to approach it and also uncover the role of prolactin and estrogen in breast nipple discharge.

Types and causes of nipple discharge

Nipple discharge refers to any fluid that comes out of one or both nipples in women who aren't pregnant or breastfeeding. While it’s often harmless and simply caused by things like frequent nipple stimulation, it can sometimes be a sign of an underlying condition, making it a bit tricky to diagnose without a proper evaluation.

Nipple discharge is generally classified into three main types:

Lactation (Milk production)

Lactation is completely normal during pregnancy and the postpartum period. During pregnancy, your breasts might begin producing milk several weeks before your baby is born. If you notice any leakage from your nipples, it’s usually what we call colostrum, which is the first form of milk your body makes to prepare for breastfeeding. This leakage is completely normal and not a cause for concern. Milk and colostrum are produced in response to hormonal and physical changes, and secretion can continue for about six months up to 2 years after giving birth or stopping breastfeeding  

Physiological discharge (Galactorrhea)

This type isn’t linked to pregnancy or breastfeeding. It is described as a milky, bilateral discharge from multiple ducts. Although it’s usually white or clear, it can appear yellow, green, brown, or grey—but not bloody.
A common cause of galactorrhea is hyperprolactinemia, which can result from medications, pituitary tumours, hormonal imbalances, or other medical issues (eg, Hypothyroidism).

Medications that are known to cause Physiologic Discharge as a result of hyperprolactinemia are, but not limited to:

• Estrogen-containing medications
• Chlorpromazine
• Fluphenazine
• Haloperidol
• Perphenazine
• Pimozide
• Aripiprazole
• Olanzapine
• Desipramine
• Sertraline
• Metoclopramide
• Domperidone
• Verapamil

That said, not everyone taking these medications will develop galactorrhea. If you’ve previously been diagnosed with hyperprolactinemia or have a history of related conditions, your doctor will likely avoid prescribing these drugs in the first place. These side effects will resolve once you stop the medication. Also, don’t forget to inform your healthcare provider if such a side effect happens.

Other causes of Galactorrhea:

• Estrogen

Estrogen plays a significant role in stimulating prolactin secretion. It does so by binding to receptors in the pituitary gland, which then interact with the prolactin gene. This explains why women, whose estrogen levels are naturally higher, have a greater prolactin response to various stimuli compared to men. Even the normal, physiologic levels of estrogen in women lead to a slightly elevated baseline prolactin level.²

• Stress

Both physical and psychological stress can trigger a small rise in your prolactin levels. Women tend to experience a bit more of an increase than men, likely because their naturally higher estrogen levels boost prolactin secretion from the pituitary. However, these stress-induced spikes are generally modest, and prolactin levels rarely go above 40 ng/mL.³

• Meals

Eating can also give your prolactin levels a slight elevation. That’s why, if your test shows only a slightly elevated prolactin level (up to 40 ng/mL in men and postmenopausal women, and up to 50 ng/mL in premenopausal women), doctors usually suggest a repeat test on an empty stomach before diagnosing hyperprolactinemia.⁴

Pathologic (suspicious) discharge

This is the one that raises red flags. It’s usually:

• Unilateral
• From a single duct
• Persistent
• Spontaneous (not caused by touching or squeezing)

The discharge can be described as clear, yellow, bloody, or blood-tinged. Common causes include:^5,6,7

• Papillomas (most frequent, 52-57% of cases): Benign growths inside breast ducts that can sometimes contain abnormal or cancerous cells
• Duct Ectasia: A benign condition, responsible for 14-33% of cases
• Breast Cancer: Found in 5-20% of cases, especially ductal carcinoma in situ (DCIS)
• Infections: Like periductal mastitis, which can cause pus-like discharge

Clinical evaluation

Every case of non-lactational nipple discharge deserves a full clinical evaluation, starting with history-taking and physical examination.⁸

What doctors will look for in a Patient's History complaining of nipple discharge:

• Is the discharge bloody or clear/milky?
• Is it spontaneous or only with nipple manipulation?
• Is it unilateral or bilateral?
• Is it from one duct or multiple ducts?

Physiological discharge is expected to be bilateral, from multiple ducts, and occurs with stimulation.
Pathologic discharge is more likely if it’s:

• Spontaneous
• Bloody
• From one duct
• In women over 40
• Associated with a lump or skin changes

It’s also important to ask about:

• Any recent breast trauma (even something as minor as a mammogram)
• Missed periods or symptoms of hormonal imbalances, like hot flashes or vaginal dryness
• Medication history—some drugs (like anticoagulants) can increase discharge or make it bloody

Diagnostic evaluation

The next steps depend on whether the discharge seems physiologic or pathologic.

For physiological discharge

If it’s bilateral and non-bloody, it’s likely benign. Still, lab tests should be done to check for possible hormonal causes, especially hyperprolactinemia.

Recommended tests

• Pregnancy test
• Prolactin levels
• Thyroid function tests
• Kidney function tests

A patient with nipple discharge might be referred to an endocrinologist if needed, especially if the patient has menstrual irregularities, infertility, headaches, vision issues, or signs of hypothyroidism.

For pathologic discharge

This includes unilateral, bloody, or mass-associated discharge. These patients should undergo breast imaging to check for any abnormalities in the ducts or breast tissue.

Usually, lab tests for galactorrhea are not needed in this group.

Imaging: What to Order and When

Approach for further diagnostic investigations will depend on age and gender:^{9,10,11,12,13,14,15}

• Women ≥40 years: Diagnostic mammography + breast ultrasound
• Women 30–39 years: Mammogram first, then ultrasound if needed
• Women <30 years: Start with ultrasound; add mammography only if there’s a suspicious finding or high-risk family history
• Men: Since nipple discharge in men has a high link to breast cancer (23-50%), both mammography and ultrasound are essential

Advanced studies

In special cases, like the ones where imaging is normal but symptoms persist, galactography or ductoscopy might be used (if available). These tests help visualise the ducts directly but usually require surgical follow-up since they don’t allow for needle biopsies.

Treatment

Physiological discharge (Galactorrhea)

Often linked to high prolactin levels, which can stem from:

• Medications (e.g., SSRIs, antipsychotics, metoclopramide)
• Pituitary tumors
• Hormonal disorders

If a medication is the cause and imaging is normal, then it's a side effect. Depending on the case, the drug can be adjusted or continued, especially if it's medically necessary.

In some cases, transient galactorrhea can occur even with normal hormone levels. This usually happens in younger women. If no other issues are found, a doctor will reassure the patient and re-evaluate in a few months.

When nipple discharge is found to be benign, like duct ectasia, it may be treated with a procedure called microdochectomy (removal of a single duct) or, in some cases, total duct excision (removal of all the ducts). If the discharge is bloody and caused by a duct papilloma, microdochectomy is usually the go-to treatment. Bloody discharge due to breast cancer, on the other hand, typically requires surgery and may also involve chemotherapy or radiation, depending on how advanced the cancer is. For purulent (pus-filled) discharge, antibiotics are usually enough, but if an abscess forms, it will need to be drained and biopsied to check the surrounding tissue.^16,17,18

FAQs

What are the common causes of nipple discharge in non-pregnant women?

Nipple discharge in non-pregnant, non-breastfeeding women can be caused by benign issues like duct ectasia or duct papillomas, often triggered by hormonal imbalances involving prolactin and estrogen. In some cases, it might also indicate more serious conditions such as breast cancer or infections. Knowing the characteristics of the discharge, whether it’s bilateral or unilateral, milky or bloody, can help guide further evaluation.

Can high prolactin levels cause nipple discharge, and is it dangerous?

High prolactin (hyperprolactinemia) can lead to nipple discharge, known as galactorrhea, even when a woman is not pregnant or breastfeeding. While it’s often benign, particularly if caused by medications, stress or pituitary tumours, it’s important to get evaluated because persistent discharge can occasionally signal an underlying issue that needs medical attention.

When should I see a doctor about nipple discharge?

You should consult a healthcare provider if you notice spontaneous nipple discharge, especially if it’s unilateral, bloody, or associated with a breast mass. Early evaluation is crucial to rule out serious conditions and to determine whether the discharge is due to benign causes, hormone imbalances, or something more concerning, like cancer.

What treatment options are available for hormone-related nipple discharge?

Treatment for nipple discharge depends on its cause. Benign conditions like duct ectasia might be managed with microdochectomy or total duct excision, while duct papillomas typically require surgical removal of the affected duct. In cases where high prolactin levels are to blame, adjusting medications or treating the underlying hormone imbalance may be recommended. For more severe cases associated with cancer, surgery, chemotherapy, or radiation therapy might be necessary.

Summary

By understanding the hormonal mechanisms behind nipple discharge, particularly the roles of prolactin and estrogen, healthcare providers can better distinguish between normal and abnormal cases. This ensures early detection of serious conditions and avoids unnecessary worry for patients experiencing a common and often harmless symptom.