Mastitis is a topic covered in the 5-Minute Clinical Consult.

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  • Mastitis is an inflammation of the breast parenchyma and possibly associated tissues (areola, nipple, subcutaneous [SC] fat).
  • Usually associated with bacterial infection (and milk stasis in the postpartum mother)
  • Usually an acute condition but can become chronic cystic mastitis


  • Predominantly affects females
  • Mostly in the puerperium; epidemic form rare in the age of reduced hospital stays for mothers and newborns
  • Neonatal form
  • Posttraumatic: ornamental nipple piercing increases risk of transmission of bacteria to deeper breast structures: Staphylococcus aureus is the predominant organism.

  • 3–20% of breastfeeding mothers develop nonepidemic mastitis.
  • Greatest incidence among breastfeeding mothers 2 to 6 weeks postpartum
  • Neonatal form occurs at 1 to 5 weeks of age, with equal gender risk and unilateral presentation.
  • Pediatric form
  • Around or after puberty
  • 82% of cases in girls

Etiology and Pathophysiology

  • Microabscesses along milk ducts and surrounding tissues
  • Inflammatory cell infiltration of breast parenchyma and surrounding tissues
  • Nonpuerperal (infectious)
    • S. aureus, Bacteroides sp., Peptostreptococcus, Staphylococcus (coagulase neg.), Enterococcus faecalis
    • Histoplasma capsulatum
    • Salmonella enterica
    • Rare case of Actinomyces europaeus
  • Puerperal (infectious)
    • Staphylococcus aureus, Streptococcus pyogenes (group A or B), Corynebacterium sp., Bacteroides sp., Staphylococcus (coagulase neg.), Escherichia coli, Salmonella sp.
    • Methicillin-resistant S. aureus (MRSA)
  • Rare secondary site for tuberculosis in endemic areas (1% of mastitis cases in these areas): single breast nodule with mastalgia
  • Corynebacterium sp. associated with greater risk for development of chronic cystic mastitis
  • Granulomatous mastitis
    • Idiopathic
      • Predilection for Asian and Hispanic women
      • Association with α1-antitrypsin deficiency, hyperprolactinemia with galactorrhea, oral contraceptive use, Corynebacterium sp. infection, and breast trauma
      • Most women have a history of lactation in previous 5 years.
    • Lupus; autoimmune
  • Puerperal
    • Retrograde migration of surface bacteria up milk ducts
    • Bacterial migration from nipple fissures to breast lymphatics
    • Secondary monilial infection in the face of recurrent mastitis or diabetes
    • Seeding from mother to neonate in cyclical fashion
  • Nonpuerperal
    • Ductal ectasia
    • Breast carcinoma
    • Inflammatory cysts
    • Chronic recurring SC or subareolar infections
    • Parasitic infections: Echinococcus; filariasis; Guinea worm in endemic areas
    • Herpes simplex
    • Cat-scratch disease
  • Lupus

Risk Factors

  • Breastfeeding
  • Milk stasis
    • Inadequate emptying of breast
      • Scarring of breast due to prior mastitis
      • Scarring due to previous breast surgery (breast reduction, biopsy, or partial mastectomy)
    • Breast engorgement: interruption of breastfeeding
  • Nipple trauma increases risk of transmission of bacteria to deeper breast structures: S. aureus predominant organism
  • Neonatal colonization with epidemic Staphylococcus
  • Neonatal
    • Bottle-fed babies
    • Manual expression of “witch’s milk”
    • Can predispose to lethal necrotizing fasciitis
  • Maternal diabetes
  • Maternal HIV
  • Maternal vitamin A deficiency (in animal models)

General Prevention

Regular emptying of both breasts and nipple care to prevent fissures when breastfeeding; also good hygiene, including hand washing and washing breast pumps after each use (1)[A]

Commonly Associated Conditions

Breast abscess

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