Mastitis is an infection and inflammation of the breast tissue that occurs most frequently while a woman is lactating and breastfeeding. It can occur when bacteria, often from the baby's mouth, enter a milk duct through a crack in the nipple. See also Mastitis While Breastfeeding.
About 1%-3% of breastfeeding mothers develop mastitis. Engorgement and incomplete breast emptying can contribute to the problem and make the symptoms worse.
Breast infections most commonly occur one to three months after the delivery of a baby, but they can occur in women who have not recently delivered as well as in women after menopause. Other causes of infection include chronic mastitis and a rare form of cancer called inflammatory carcinoma.
In healthy women, mastitis is rare. However, women with diabetes, chronic illness, AIDS, or an impaired immune system may be more susceptible.