The condition usually occurs in women who are breast-feeding. Bacteria are normally present on the nipple and in a baby's mouth. They can enter the breast through a cracked nipple or the milk ducts and cause mastitis.
Many factors can make a breast-feeding mother susceptible to mastitis.
One of the principal factors is inadequate drainage of milk from your breasts. Poor emptying can occur by allowing too much time to pass between feedings. Also, milk may not drain well if a duct is clogged, or a tight- fitting bra may obstruct milk flow. Injury to the breast can make a breast-feeding woman more susceptible to mastitis. The injury may be caused by a baby teething on the breast or incorrectly latching on to the nipple.