Mammary duct ectasia often doesn't cause any signs or symptoms. If you do experience signs and symptoms, you may notice:

• A dirty white, greenish or black nipple discharge from one or both nipples
• Tenderness in the nipple or surrounding breast tissue
• Redness of the nipple and sometimes the surrounding area
• A breast lump or thickening near the clogged duct
• A nipple that's turned inward (inverted)

A bacterial infection called mastitis also may develop in the affected milk duct, causing breast tenderness, inflammation in the area around the nipple (areola) and fever. Signs and symptoms of mammary duct ectasia may improve on their own.

Your breasts are made up of connective tissues that include a system of milk ducts — tiny passages that carry milk to the nipples. Mammary duct ectasia occurs when a milk duct beneath the nipple widens, becoming blocked or clogged with a sticky substance and inflamed.

Experts don't know exactly what causes mammary duct ectasia. Some speculate the cause to be associated with:

• Breast tissue changes due to aging. As you age, the composition of your breast tissue changes from mostly glandular to mostly fatty in a process called involution. These normal breast changes can sometimes lead to a blocked milk duct and the inflammation associated with mammary duct ectasia.
• Smoking. Cigarette smoking may be associated with widening of milk ducts, which can lead to inflammation and, possibly, mammary duct ectasia.

Nipple inversion. A newly inverted nipple may obstruct milk ducts, causing inflammation and infection. A nipple that's newly inverted could also be a sign of a more serious underlying condition, such as cancer.

Complications of mammary duct ectasia are usually minor and often more bothersome than serious. These may include:

• Nipple discharge. Nipple discharge caused by mammary duct ectasia can be frustrating. Fluid leaking from your nipples can cause embarrassing wetness and staining on your clothes.
• Breast discomfort. Mammary duct ectasia can cause redness, swelling and tenderness around your nipples.
• Infection. A bacterial infection (periductal mastitis) may develop in the affected milk duct, sometimes causing pain in or around the nipple, a general feeling of illness (malaise) or a fever. Untreated infection could lead to an abscess — a collection of pus in your breast tissue — which may require a procedure to drain it.
• Concern about breast cancer. When you notice a change in your breast, you may worry that it's a sign of breast cancer, especially if you develop a hard lump around a milk duct affected by mammary duct ectasia. While it's important to get signs and symptoms checked out promptly, remember that mammary duct ectasia does not increase your risk of breast cancer