Nipple discharge, the leaking of fluid from the breast, is a common symptom that often causes concern. In the vast majority of cases, this fluid is not related to breast cancer. The breast ducts naturally produce and transport fluid, meaning many benign conditions, including hormonal fluctuations, can lead to discharge. Understanding the nature of the discharge is the first step in determining its cause, which is usually non-cancerous.
Differentiating Types of Nipple Discharge
Assessing the physical characteristics of the discharge, independent of its color, is a primary step for medical evaluation. Discharge is categorized as either spontaneous or expressed. Spontaneous discharge leaks without manipulation and is considered more significant, warranting closer attention than discharge that occurs only when the nipple or breast is squeezed (expressed discharge).
The location is also a differentiator: unilateral (one breast) or bilateral (both breasts). Providers also determine if the fluid originates from a single duct opening or multiple ducts. A discharge that is spontaneous, unilateral, and originates from a single duct is more likely associated with an underlying structural change. Conversely, discharge that is bilateral and comes from multiple ducts is usually classified as physiologic, meaning it is a normal function of the breast glands.
Color and Consistency What Discharge Colors Indicate
The color of the discharge provides a clue about the underlying process, though no single color confirms or rules out cancer. Discharge that is bloody (sanguineous) or clear/watery (serous) from a single duct is associated with a higher risk profile and requires investigation. This appearance is often linked to a benign growth inside a milk duct, but it can occasionally be a sign of malignancy.
In contrast, discharge presenting as milky white, green, yellow, or dark brown/black is overwhelmingly caused by benign conditions. Milky white discharge, known as galactorrhea, is typically related to elevated hormone levels, which stimulate milk production outside of pregnancy or breastfeeding. Green, yellow, or dark brown discharge is frequently a result of trapped fluid and cellular debris within the milk ducts. These colors are often seen with common, non-cancerous changes in the breast tissue.
Common Underlying Causes of Nipple Discharge
The most frequent cause of single-duct, bloody, or clear discharge is a benign growth called an intraductal papilloma. This small, non-cancerous, wart-like tumor grows inside the milk duct. Its fragility can lead to the spontaneous leaking of blood or clear fluid.
A common benign cause of green, yellow, or dark-colored discharge is mammary duct ectasia, a condition where the milk ducts widen and their walls thicken. This widening allows fluid and inflammatory material to accumulate, which can then be expressed as a thick, often multicolored, discharge. Milky discharge, or galactorrhea, is most often a systemic issue, frequently caused by hormonal imbalances, such as high levels of the hormone prolactin. Certain prescription medications, including some antipsychotics and high blood pressure drugs, can also raise prolactin levels and induce this bilateral milky discharge.
Fibrocystic changes, involving the development of fluid-filled sacs and fibrous tissue, can result in discharge that is typically green or yellow. While discharge is a recognized symptom of breast cancer, particularly ductal carcinoma in situ, it is a relatively rare presentation, accounting for less than 10% of all cases. When cancer is the cause, the discharge is most often persistent and spontaneous.
When to Seek Medical Evaluation
Any persistent discharge, especially if it is new and not related to pregnancy or breastfeeding, should be brought to the attention of a healthcare provider for assessment. Certain features signal the need for a prompt evaluation, regardless of the discharge color.
A discharge accompanied by other concerning symptoms, such as a new lump, changes in the skin of the breast, or a newly inverted nipple, requires immediate attention. The diagnostic process typically begins with a thorough clinical breast examination and imaging, such as a diagnostic mammogram and a targeted ultrasound of the area behind the nipple. In some cases, a procedure called ductography, or a breast magnetic resonance imaging (MRI), may be performed to visualize the duct system and help pinpoint the exact cause of the discharge.