Nipple discharge refers to any fluid that seeps out of the nipple of the breast.

Nipple discharge during pregnancy and breast-feeding is normal. Nipple discharge happens less commonly in women who aren't pregnant or breast-feeding. It may not be cause for concern, but it's wise to have it evaluated by a doctor to be sure. Men who experience nipple discharge under any circumstances should be evaluated.

One or both breasts may produce a nipple discharge, either spontaneously or when you squeeze your nipples or breasts. Nipple discharge may look milky, clear, yellow, green, brown or bloody. Discharge that isn't milk comes out of your nipple through the same ducts that carry milk. The discharge can involve a single duct or multiple ducts. The consistency of nipple discharge can vary — it may be thick and sticky or thin and watery.

Nipple discharge is a normal part of breast function during pregnancy or breast-feeding. It may also be associated with menstrual hormone changes and fibrocystic changes. The milky discharge after breast-feeding will normally affect both breasts and can continue for up to two or three years after stopping nursing.

A papilloma is a noncancerous (benign) tumor that can be associated with bloody discharge. The discharge associated with a papilloma often occurs spontaneously and involves a single duct. Although the bloody discharge may resolve on its own, your doctor will likely recommend a diagnostic mammogram and a breast ultrasound to see what's causing the discharge. You may also need a biopsy to confirm that it's a papilloma or to exclude a cancer. If the biopsy confirms a papilloma, your doctor will refer you to a surgeon to discuss treatment options.

Often, nipple discharge stems from a benign condition. However, breast cancer is a possibility, especially if:

• You have a lump in your breast
• Only one breast is affected
• The discharge contains blood or is clear
• The discharge is spontaneous and persistent
• The discharge affects only a single duct

Possible causes of nipple discharge include:

• Abscess
• Birth control pills
• Breast cancer
• Breast infection
• Ductal carcinoma in situ (DCIS)
• Endocrine disorders
• Excessive breast stimulation
• Fibrocystic breasts (lumpy or rope-like breast tissue)
• Galactorrhea
• Injury or trauma to the breast
• Intraductal papilloma (a benign, wartlike growth in a milk duct)
• Mammary duct ectasia
• Medication use
• Menstrual cycle hormone changes
• Paget's disease of the breast
• Periductal mastitis
• Pregnancy and breast-feeding
• Prolactinoma

Nipple discharge is rarely a sign of breast cancer. But it might be a sign of an underlying condition that requires treatment.

If you're still having menstrual periods and your nipple discharge doesn't resolve on its own after your next menstrual cycle and occurs spontaneously, make an appointment with your doctor to have it evaluated.

If you're past menopause and you have a spontaneous nipple discharge from a single duct in one breast only, see your doctor right away for evaluation.

In the meantime, take care to avoid nipple stimulation — including frequent checks for discharge — because stimulation can result in persistent nipple discharge.