Nipple discharge is the third most common breast complaint for which women seek medical attention, after lumps and breast pain. A woman's breasts secret some fluid throughout most of the adult life. The difference between lactating (milk producing) and non-lactating breasts is mainly in the degree or amount of secretion and to a smaller degree the chemical composition of the fluid. In non-lactating women, small plugs of tissue block the nipple ducts and keep the nipple from discharging fluid. Nipple discharge are often yellow, green, brown, bloody, or milky in appearance.

Importantly, most nipple discharges, while often bothersome, are not cancerous. However, any woman with a suspicious or worrisome nipple discharge (see below) should consult her physician.

Nipple Discharge is of Concern if it is:

1. bloody or watery (serous) with a red, pink, or brown color
2. sticky and clear in color or brown to black in color (opalescent)
3. appears spontaneously without squeezing the nipple
4. persistent
5. on one side only (unilateral)
6. a fluid other than breast milk

Causes of Nipple Discharge

Milky discharge (cloudy, whitish or almost clear in color, thin, non-sticky) is the most common type of discharge. Most milky discharge is caused by lactation or increased mechanical stimulation of the nipple due to fondling, suckling or irritation from clothing during exercise or activity. Drugs or hormones that stimulate prolactin secretion can cause spontaneous, persistent production of milk (galactorrhea). Prolactin is the hormone produced by the pituitary gland that starts the growth of the mammary glands and triggers production of milk. Some pituitary tumors cause excess prolactin secretion that can lead to milky nipple discharge, usually from both breasts (bilateral).  Opalescent discharge that is yellow or green in color is normal.

Most bloody or watery (serous) nipple discharge (approximately 90%) is due to a benign condition such as papilloma or infection. A papilloma is a non-cancerous, wart-like tumor with a branching or stalk that has grown inside the breast duct. Papillomas frequently involve the large milk ducts near the nipple. Multiple papillomas may also be found in the small breast ducts further from the nipple.

Of the benign conditions that cause suspicious nipple discharge, approximately half is due to papilloma and the other half is a mixture of benign conditions such as fibrocystic conditions (i.e., lumpy) or duct ectasia (widening and hardening of the duct due to age or damage). For example, women with fibrocystic breasts may experience clear, yellow or light green discharge. Most opalescent discharge is due to duct ectasia or cyst.

Suspicious nipple discharge is due to cancer in about 10% of cases. That means, the vast majority nipple discharges are noncancerous. Discharge caused by a malignant condition is commonly on one side only. However, papillomas usually causes discharge from a single breast duct, so certainly not all unilateral discharges are associated with cancer. Nipple discharge can also be associated with a rare form of cancer called Paget's disease of the nipple.

Signs of Paget's disease usually only occur on one nipple and may include:

• persistent crustiness, scaliness, or redness of the nipple
• itching or burning of the nipple and surrounding areola
• bleeding or oozing from the nipple and areola

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