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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 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 irritated. 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 3% to 5% of nursing 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 then can 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. Sometimes, women and their physicians confuse mastitis with breast engorgement, or the tenderness and redness that appears when milk builds up in the breasts. Mastitis often can be distinguished if symptoms are accompanied by fever.


A number of antibiotics are used to treat mastitis, including cephalexin, amoxicillin, azithromycin, dicloxacillin, and clindamycin. Breastfeeding usually 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. Keeping the breast clean before breastfeeding also helps prevent infection. Keeping the breasts from becoming engorged may help prevent mastitis by preventing plugging of milk ducts.



Hager, W. David. "Managing Mastitis: Antibiotics Can Prove Invaluable in the Treatment of Mastitis, but Before You Prescribe Them, It's Important to Distinguish Breast Engorgement from Infectious Mastitis." Contemporary OB/GYN January 2004: 32-41.


La Leche League International. 1400 N. Meacham Rd., Schaumburg, IL 60173-4048. (800) 525-3243.


inflammation of the breast, occurring in a variety of forms and degrees of severity. fibrocystic disease of the breast (called also chronic cystic mastitis) is the most common disorder of the breast resulting from hormonal imbalance. It generally occurs in women between the ages of 35 and 50, is probably related to the activity of the ovaries, and is rare after menopause. Occasionally mastitis becomes so severe as to require a mastectomy.

Young girls whose breasts are maturing sometimes experience a painful swelling and hardness of the breast, known as puberty mastitis; this is rarely serious and usually resolves within a few weeks. Occasionally a cloudy liquid may be squeezed from the nipples. It is best to wear a brassiere that gives mild support but does not irritate.

A mild inflammation known as stagnation mastitis, or caked breast, may occur during the early lactation period. Glands of the breast can become congested with milk, with formation of painful lumps.

Acute mastitis may occur after childbirth, when it is known as puerperal mastitis. This is an infection that usually results from the presence of staphylococci, or occasionally streptococci, which enter through cracks in the skin of the breast, particularly of the nipples. The breasts are tender, red, and warm and become swollen and painful. The inflammation responds quickly to sulfonamide medicines or other antibiotics, but in some cases an abscess may develop which must be incised and drained.

A galactocele, or milk cyst, sometimes develops during lactation. It is probably caused by obstruction of a duct and can be removed after the baby has been weaned.

There are other types of infectious mastitis not related to lactation. Inflammation of the breast sometimes accompanies mumps, particularly in adults. Tuberculous mastitis usually occurs in young women and accompanies tuberculosis of the lungs or of the cervical lymph nodes. Treatment is with antibiotics, although surgery is sometimes necessary.

A condition that may occur at the time of menopause or later in women who have had children is mammary duct ectasia, or comedomastitis, which is distention of the milk-producing ducts caused by the caking of secretions; some of the material may be discharged from the nipple. Eventually this may develop into plasma cell mastitis. The breast may be tender and painful, with lump formation, nipple retraction, change in contour, and possibly a cloudy discharge from the nipple.
chronic cystic mastitis fibrocystic disease of the breast.


Inflammation of the breast.
Synonym(s): mastadenitis
[masto- + G. -itis, inflammation]


/mas·ti·tis/ (mas-ti´tis) inflammation of the breast.
mastitis neonato´rum  any abnormal condition of the breast in the newborn.
periductal mastitis  inflammation of the tissues about the ducts of the mammary gland.
plasma cell mastitis  infiltration of the breast stroma with plasma cells and proliferation of the cells lining the ducts.


Inflammation of a mammary gland or udder, usually caused by infection.

mas·tit′ic (-tĭt′ĭk) adj.


Etymology: Gk, mastos, breast, itis, inflammation
an inflammatory condition of the breast, usually caused by streptococcal or staphylococcal infection. Acute mastitis, most common in the first 2 months of lactation, is characterized by pain, swelling, redness, axillary lymphadenopathy, fever, and malaise. If it is untreated or inadequately treated, abscesses may form. Antibiotics, rest, analgesia, and warm soaks are usually prescribed. Usually breastfeeding may continue. Chronic tuberculous mastitis is rare; when it occurs, it represents extension of tuberculosis from the lungs and ribs beneath the breast.
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Inflammation of breast tissue, which is most often due to bacterial infection—most commonly Staphylococcus aureus, less commonly S epidermidis and streptococci—typically in a background of breast-feeding.
Warm wet compresses, oral antibiotics.


Breast inflammation, often bacterial, often staphylococcal, often during breast-feeding Management Warm wet compresses, oral antibiotics. See Breast abscess, Plasma cell mastitis.


Inflammation of the breast.
Synonym(s): mastadenitis.
[masto- + G. -itis, inflammation]


Inflammation of the breast. This is commonest during LACTATION and is usually caused by infection with organisms such as Staphylococcus aureus entering through cracks or abrasions in the nipples. There is high fever, redness, hardening and tenderness. Treatment is with antibiotics but an abscess may form which may have to be drained surgically.

mastitis (mas·tīˑ·tis),

n an inflammation within the mammary glands; caused by staphylcoccal or streptococcal infection; treated with warm soaks, rest, analgesia, and antibiotics. Also called
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inflammation of the mammary gland. Although it may be caused by chemical or physical agents, the causes are almost entirely infectious, and mostly bacterial. Clinical signs vary with the severity of the disease, but include pain, heat and swelling of the affected quarter or half or gland, and abnormality of the milk, either as clots or flakes, and wateriness of the liquid phase. Subclinical mastitis is the most important form and is diagnosed on the basis of bacteriological examination or by indirect tests, principally based on the cell count of the milk. Called also mammitis, garget. See also blue breast.
For a summary of the infectious agents which cause mastitis in each of the animal species consult Table 16. See also california mastitis test, wisconsin mastitis test.

acute mastitis
acute swelling of the mammary gland accompanied by heat and pain, together with grossly abnormal milk. There may be a slight systemic reaction.
black mastitis
severe, usually peracute clinical mastitis in which one or more quarters become gangrenous. Usually caused by Staphylococcus aureus.
botryomycotic mastitis
persistent local infection, usually by Staphylococcus aureus, causes granulomas and the collection of pus within them to produce a botryomycotic effect. See also coliform mastitis.
coliform mastitis
caused by Escherichia coli, Klebsiella spp. or Enterobacter aerogenes. See coliform mastitis.
contagious mastitis
caused by those bacteria which are resident in bovine udders or on teat skin and are spread primarily during milking. Staphylococcus aureus, Streptococcus agalactiae, S. dysgalactiae are the common causes. Called also 'cow-associated' mastitis.
mastitis control
aimed at reducing new infection rate and the static quarter infection rate; based on dry period treatment, culling or treating infected animals, teat disinfection, teat cup liner sanitization, and milking machine maintenance and correct use.
discarding mastitis milk
milk from infected quarters flushed to waste, not fed to calves.
mastitis dry cow treatment
intramammary infusion with a long-acting formulation, at the time of the last milking for the lactation; may be blanket (all cows) or selective (infected quarters only). See also dry period treatment.
environmental mastitis
caused by those bacteria which are usually resident in the environment of the cow, especially in the feces, bedding or water. Escherichia coli, Streptococcus uberis are the common infections. See also coliform mastitis.
gangrenous mastitis
the teat and much of the quarter are black and cold, the secretion is thin blood-stained fluid and there is a severe systemic reaction. The quarter is lost, and the cow may very well die.
granulomatous mastitis
see botryomycotic mastitis (above).
mastitis infection rate
rate of quarters or cows infected with pathogenic bacteria or showing clinical mastitis or, a much more commonly used index nowadays, the percentage of cows with a milk cell count in excess of a stated norm.
NIRD mastitis control program
the basis of all modern mastitis control programs. Named after the National Institute for Research in Dairying (now called the Animal Grassland Research Institute) at Reading, UK, which introduced dry period treatment and teat dipping into mastitis control. Highly effective in reducing the prevalence of contagious mastitis pathogens such as Streptococcus agalactiae, Staphylococcus aureus. Called also 'five point program'.
peracute mastitis
as for acute mastitis, but there is also a severe systemic reaction and the cow may die of the attending septicemia.
pyogranulomatous mastitis
a chronic disease in cattle caused by Nocardia asteroides, also occurs in sows caused by Actinomyces suis.
mastitis screening
testing for evidence of inflammation of mammary epithelium, of individual cows or entire herd, by use of milk cell counts, biochemical tests which measure products of inflammation, e.g. NAG-ase test, electrical conductivity.
subclinical mastitis
mastitis in which the only evidence of disease is an abnormality of cell count or other clinicopathological parameter.
summer mastitis
a serious disease likely to cause the loss of the quarter and a severe clinical illness. Caused by Arcanobacterium pyogenes and other unspecified cocci. See also Table 16.
suppurative mastitis
mastitis in which the secretion of the quarter is largely pus.
traumatic mastitis
mastitis in which the infection is introduced through the skin into the teat canal or mammary tissue by a penetrating injury; it is usually a mixed infection and causes a suppurative or gangrenous mastitis, depending on the bacteria that are present. The quarter is ruined and the cow may die. See also Table 16.
mastitis treatment withholding times
after intramammary infusion in lactating cow—withhold 72 hours; dry cow intramammary infusion—administered at least 4 weeks before calving, withhold for 96 hours after calving.
mastitis vaccination
not proven to exert beneficial effect. Only vaccination with an autogenous bacterin against Staphylococcus aureus, where the infecting organism is highly antigenic, appears to even reduce the severity of the disease.