Nipple discharge is fluid from the nipple, with or without squeezing the breast. The discharge can be milky, clear, green, purulent, bloody, or faintly yellow. The consistency can be thick, thin, sticky, or watery.

Nipple discharge may be normal, such as milk in late pregnancy or after childbirth, and in newborns during the first weeks of life. It may also be normal following squeezing, in women during the reproductive years. It is likely abnormal if it occurs in men, contains blood, is from only one breast, or is associated with a breast lump, swelling, redness or overlying skin changes. Reasons for abnormal discharge include an intraductal papilloma, duct ectasia, blocked milk duct, infected breast (mastitis or breast abscess), breast cancer, certain medications, and conditions that raise prolactin.

Milky discharge in a non-pregnant, non-breast feeding women is evaluated differently to other abnormal nipple discharge. Often, the cause can be determined based on symptoms and examination. Blood tests may be done to rule out low thyroid or high prolactin. Other tests may include mammography, breast ultrasound, breast biopsy, or skin biopsy.

Treatment depends on the underlying cause. Duct ectasia may be treated with surgical removal of the ducts involved. Infectious causes may require antibiotics or incision and drainage. Nipple discharge is the third most common breast complaint by women, after breast pain and a breast lump. About 3% of breast cancer cases are associated with discharge.