Fluid that leaks from one or both nipples is called nipple discharge. Each breast has several (15 to 20) milk ducts. A discharge can come from one or more of these ducts.
(See also Overview of Breast Disorders Overview of Breast Disorders Breast disorders may be noncancerous (benign) or cancerous (malignant). Most are noncancerous and not life threatening. Often, they do not require treatment. In contrast, breast cancer can mean... read more 
.)
Nipple discharge can occur normally during the last weeks of pregnancy and after childbirth when breast milk is produced. A nipple discharge can also be caused by breast stimulation in women who are not pregnant or breastfeeding, especially during the reproductive years. However, a nipple discharge in men is always abnormal.
A normal nipple discharge is usually a thin, cloudy, whitish, or almost clear fluid. However, the discharge may be other colors, such as gray, green, yellow, or brown. A bloody discharge is abnormal.
Abnormal discharges vary in appearance depending on the cause. An abnormal discharge may be accompanied by other abnormalities, such as dimpled skin, swelling, redness, crusting, sores, and an inverted (retracted) nipple. (A nipple is inverted if it pulls inward and does not return to its normal position when it is stimulated.) If a discharge from only one breast occurs on its own (without any stimulation of the nipple), it is considered abnormal.
Causes of Nipple Discharge
Several disorders can cause an abnormal discharge.
A discharge from one milk duct or from one breast is likely to be caused by a problem with that breast, such as a noncancerous (benign) tumor or, less commonly, a cancerous (malignant) breast tumor Breast Cancer Breast cancer occurs when cells in the breast become abnormal and divide uncontrollably. Breast cancer usually starts in the glands that produce milk (lobules) or the tubes (ducts) that carry... read more 
.
A discharge from both breasts or from several milk ducts in one breast is more likely to be caused by a problem outside the breast, such as a hormonal disorder or use of certain drugs.
Common causes of a nipple discharge
Usually, the cause is a benign disorder of the milk ducts, such as the following:
A benign tumor in a milk duct (intraductal papilloma)
Dilated milk ducts (mammary duct ectasia)
Fibrocystic changes Fibrocystic Changes of the Breast Fibrocystic changes of the breast (formerly called fibrocystic breast disease) include breast pain, cysts, and lumpiness that are not due to cancer. (See also Overview of Breast Disorders and... read more , including pain, cysts, and general lumpiness
Intraductal papilloma is the most common cause. It is also the most common cause of a bloody nipple discharge when there is no lump in the breast.
Less common causes of a nipple discharge
Certain disorders stimulate the production of breast milk in women who are not pregnant or breastfeeding (see table Some Causes and Features of Nipple Discharge Some Causes and Features of Nipple Discharge 
). In most of these disorders, the level of prolactin (a hormone that stimulates production of breast milk) is elevated. Taking certain drugs can have the same effect.
Cancer causes fewer than 10% of cases.
Evaluation of Nipple Discharge
Warning signs
Nipple discharge is a cause for concern when it
Is accompanied by a lump that can be felt
Is bloody or pink
Comes from only one breast
Occurs without the nipple's being squeezed or stimulated by other means (when it occurs spontaneously)
Occurs in women aged 40 or older
Occurs in a boy or man
When to see a doctor
If a nipple discharge continues for more than one menstrual cycle or if any of the warning signs are present, women (or men) should see a doctor. Delay of a week or so is not harmful unless there are signs of infection such as redness, swelling, and/or a discharge of pus. Women with such symptoms should see a doctor within 1 or 2 days.
What the doctor does
Doctors first ask questions about the woman's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the discharge and the tests that may need to be done (see Table below).
To help identify the cause, doctors ask about the discharge and about other symptoms that may suggest possible causes. They ask
Whether the discharge comes from one or both breasts
What the discharge's color is
How long it has lasted
Whether it is spontaneous or occurs only when the nipple is stimulated
Whether a lump Breast Lumps A breast lump (mass) is a thickening or bump that feels different from surrounding breast tissue. A lump may be discovered by a woman or during a routine physical examination by a doctor. (See... read more or breast pain Breast Pain Many women experience breast pain. Breast pain may occur in one or both breasts. (See also Overview of Breast Disorders.) Likely causes of breast pain depend on whether the pain is felt in a... read more is present
Women are also asked whether they have had disorders or take drugs that can increase prolactin levels.
Doctors examine the breast, looking for abnormalities, including lumps Warning signs A breast lump (mass) is a thickening or bump that feels different from surrounding breast tissue. A lump may be discovered by a woman or during a routine physical examination by a doctor. (See... read more . If the discharge does not occur spontaneously, the area around the nipples is gently pressed to try to stimulate a discharge.
Doctors also feel the lymph nodes in the armpits and above the collarbone to check for enlarged lymph nodes.
Testing
If doctors suspect that a hormonal disorder is the cause, blood tests are done to measure the levels of prolactin and thyroid-stimulating hormone.
If a pituitary or brain disorder is suspected, magnetic resonance imaging (MRI) or computed tomography (CT) of the head is done.
If the discharge is not obviously bloody, it is analyzed to determine whether it contains small amounts of blood. If blood is present, a sample of the discharge is examined under a microscope (called cytology) to look for cancer cells.
If a lump can be felt, ultrasonography or mammography is done. Testing Testing A breast lump (mass) is a thickening or bump that feels different from surrounding breast tissue. A lump may be discovered by a woman or during a routine physical examination by a doctor. (See... read more is similar to that for any breast lump.
Cysts are drained (by aspiration), and the fluid is tested. If the fluid is bloody, it is checked for cancer cells.
If lumps are solid, mammography is done, followed by a biopsy.
When there is no lump but cancer is still suspected or when other test results are unclear, mammography is done.
If test results after aspiration, ultrasonography, or mammography are abnormal, a biopsy is done.
If ultrasonography and mammography do not identify a cause and the discharge occurs spontaneously and comes from one milk duct, doctors usually do a special type of mammogram (called a ductogram, or galactogram). For this procedure, a contrast agent (which helps make images clearer) is injected into the duct, and images are taken, just as for a regular mammogram. This test can help rule out or identify cancer.
If no lump can be felt and the mammogram is normal, cancer is highly unlikely.
Sometimes a specific cause cannot be identified.
If women have any of the following, they should see a doctor who is experienced in managing breast disorders:
A lump in the breast
A bloody or pink discharge
A spontaneous discharge from one breast
An abnormality previously detected by mammography or ultrasonography
Treatment of Nipple Discharge
If a disorder is identified, it is treated.
If a noncancerous tumor or disorder is causing a discharge from one breast, the duct that the discharge is coming from may be removed. This procedure requires only a local anesthetic and does not require an overnight stay in the hospital.
Key Points
Usually, the cause of nipple discharge is not cancer.
If the discharge comes from both breasts or from several milk ducts and is not bloody or pink, the cause is usually a noncancerous hormonal disorder.
If the discharge comes from only one breast and is bloody or pink, cancer is possible, especially in women aged 40 or older.
Whether blood tests, imaging (such as ultrasonography), or both, are done depends on the suspected cause.
