Mastitis is an inflammation of the breast that occurs most commonly in breast-feeding women. It may be caused by breast engorgement, a blocked milk duct, or cracked skin on the woman's nipples that allows bacteria to enter the breast. In women who are not breast-feeding, it is related to changes that occur with aging, such as expanded (dilated) or irregular milk ducts.

Symptoms of mastitis may include:

• Increased pain, swelling, redness, or warmth in an area of a breast.
• Red streaks extending from a breast.
• Drainage of pus from a breast.
• Swollen lymph nodes in the neck or armpit.
• Flu-like symptoms, such as fever, chills, and fatigue.

Mastitis will not go away without treatment. Most women can safely continue to breast-feed or pump breast milk while being treated. Treatment usually involves a combination of antibiotics and home treatment to increase the flow of milk through the breast and relieve discomfort while the infection clears up. In some cases, a breast abscess (a pocket of infection) may form. An abscess may need to be drained by a doctor, and the woman may need to stop breast-feeding for a few days while the infection is treated.

Breast infections never lead to cancer, but some breast cancers look like infections.