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Definition, Description, Causes and symptoms, Diagnosis, Treatment, Prognosis, Prevention

Mastitis is an infection of the breast. It usually only occurs in women who are breastfeeding their babies.


Breastfeeding is the act of allowing a baby to suckle at the breast, in order to drink the mother's milk. In the process, unaccustomed to the vigorous pull and tug of the infant's suck, the nipples may become sore, cracked, or slightly abraded. This creates a tiny opening in the breast, through which bacteria can enter. The presence of milk, with high sugar content, gives the bacteria an excellent source of nutrition. Under these conditions, the bacteria are able to multiply, until they are plentiful enough to cause an infection within the breast.

Mastitis usually begins more than two to four weeks after delivery of the baby. It is a relatively uncommon complication of breastfeeding mothers, occurring in only approximately 2% of women.

Causes and symptoms

The most common bacteria causing mastitis is called Staphylococcus aureus. In 25-30% of people, this bacteria is present on the skin lining normal, uninfected nostrils. It is probably this bacteria, clinging to the baby's nostrils, that is available to create infection when an opportunity (crack in the nipple) presents itself.

Usually, only one breast is involved. An area of the affected breast becomes swollen, red, hard, and painful. Other symptoms of mastitis include fever, chills, and increased heart rate.


Diagnosis involves obtaining a sample of breast milk from the infected breast. The milk is cultured, allowing colonies of bacteria to grow. The causative bacteria can then be specially prepared for identification under a microscope. At the same time, tests can be performed to determine what type of antibiotic would be most effective against that particular bacteria.

Mastitis is usually caused by a bacterial infection through a nipple damaged during breastfeeding. (Photograph by Dr. P. Marazzi, Photo Researchers, Inc. Reproduced by permission.) Mastitis is usually caused by a bacterial infection through a nipple damaged during breastfeeding. (Photograph by Dr. P. Marazzi, Photo Researchers, Inc. Reproduced by permission.)


The antibiotics dicloxacillin and erythromycin are both used to treat mastitis. Breastfeeding should be continued, because the rate of abscess formation (an abscess is a persistent pocket of pus) in the infected breast goes up steeply among women who stop breastfeeding during a bout with mastitis. Most practitioners allow women to take acetaminophen while nursing, to relieve both fever and pain. As always, breastfeeding women need to make sure that any medication they take is also safe for the baby, since almost all drugs they take appear in the breastmilk. Warm compresses applied to the affected breast can be soothing.


Prognosis for uncomplicated mastitis is excellent. About 10% of women with mastitis will end up with an abscess within the affected breast. An abscess is a collection of pus within the breast. This complication will require a surgical procedure to drain the pus.


The most important aspect of prevention involves good handwashing to try to prevent the infant from acquiring the Staphylococcus aureus bacteria in the first place.



Current Obstetric & Gynecologic Diagnosis & Treatment. Ed. Alan H. DeCherney. Norwalk, CT: Appleton & Lange, 1994.

Williams Obstetrics. Ed. F. Gary Cunningham, et al. Stamford: Appleton & Lange, 1997.


LaLeche League International. 1400 N. Meacham Rd., Schaumburg, IL 60173-4048. (800) 525-3243. <http://www.lalecheleague.org>.

Rosalyn Carson-DeWitt, MD

Additional topics

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