Mastitis may be caused by:

  • A blocked milk duct. If a breast doesn't completely empty at feedings, one of your milk ducts can become clogged, causing milk to back up, which leads to breast infection.
  • Bacteria entering your breast. Bacteria from your skin's surface and baby's mouth can enter the milk ducts through a break or crack in the skin of your nipple or through a milk duct opening. Bacteria can multiply, leading to infection. These germs aren't harmful to your baby — everyone has them. They just don't belong in your breast tissues.
Jul. 18, 2012