As a woman nears menopause, the mammary ducts located under the nipple become dilated. This normal process of dilation of the milk gland is called ectasia. Ectasia is a noncancer breast condition. In some cases, it can lead to a blockage of the ducts. Then fluid may become pooled and leak into the nearby tissue. This causes infection, chronic inflammation, or a pus-filled infection called an abscess. If there is an infection, it may cause scar tissue to form. This draws the nipple inward. This infection may also cause breast pain and thick, sticky nipple discharge.
Some other symptoms you might have with nipple discharge include:

  • breast pain or tenderness
  • lump or swelling in the breast or around the nipple
  • nipple changes, like turning inward, dimpling, changing color, itching, or scaling
  • skin changes, such as rash or lesions
  • redness
  • breast size changes, such as one breast that’s larger or smaller than the other
  • fever
  • missed periods
  • nausea or vomiting
  • fatigue

Nipple discharge and cancer

Nipple discharge can be a symptom of breast cancer. Women who report nipple discharge of unknown origin, between 7 and 15 percent will have breast cancer. For the vast majority of women, this means that nipple discharge is not due to cancer. The most common diagnoses for women with cancerous nipple discharge, however, are ductal carcinoma in situ or papillary carcinoma.
If a doctor is unable to establish a clear benign underlying cause for nipple discharge, they will usually recommend an imaging scan to confirm a potentially cancerous lesion is not present. If a person who is at higher risk for breast cancer due to family history experiences nipple discharge, they should speak to their doctor as soon as possible.

Other causes of nipple discharge include:

  • birth control pills
  • breast infection or abscess
  • drugs that increase levels of the milk-producing hormone prolactin, such as antidepressants and tranquilizers
  • excess stimulation of the breast or nipple
  • hormone changes during your period
  • injury to the breast
  • prolactinoma, a noncancerous tumor of the pituitary gland
  • underactive thyroid gland
  • breast cancer

Once you know what’s causing the nipple discharge, you can treat it if necessary. Discharge that’s due to pregnancy, breastfeeding, or hormonal changes may not need to be treated. Your doctor may treat discharge from other causes based on the condition.