What is mastitis?

Mastitis is an infection in the breast that results in inflammation and pain. It can occur in both non-breastfeeding women and breastfeeding women. It affects up to one in 10 women who are breastfeeding their babies. Mastitis while breastfeeding is sometimes called puerperal mastitis or lactation mastitis. In those who are not breastfeeding, it is called periductal mastitis.

What causes mastitis?

In women who are not breastfeeding, a bacterial infection can cause mastitis. Infections can result from a cracked or sore nipple or a nipple piercing. In the case of a cracked or sore nipple, bacteria can seep in through the milk ducts. This kind of infection typically occurs in females in their late 20s to early 30s. Periductal mastitis happens more often in those who smoke. The infection also can occur because of duct estasia (the shortening and widening) of milk ducts behind the nipple. These changes come as breasts age.

As for mastitis in breastfeeding females, it can result when milk ducts experience a build-up of milk (milk stasis). Build-up of milk results when breast milk is not efficiently removed from the breast. Among the causes of milk stasis are:

  • Sucking problems for the baby.
  • Improper attachment of the baby to the breast.
  • The baby’s favoring of one breast over the other.
  • Pressure on the breast.
  • Feedings that are missed or infrequent.

The body’s immune system registers proteins in the milk as being a viral or bacterial infection. Breasts become inflamed in order to stop the infection from spreading.

What are the symptoms of mastitis?

Mastitis symptoms can include:

  • Nipple discharge.
  • A red or swollen area on the breast.
  • A hard lump or area in the breast.
  • Flu-like symptoms including aches, chills, and tiredness.

Last reviewed by a Cleveland Clinic medical professional on 10/15/2014.


  • NHS Choices. Mastitis Accessed 10/15/2014.

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