Mastitis is inflammation of the breast tissue with or without infection. The most common form of mastitis is associated with lactation in the first few weeks after birth. Non-lactational mastitis includes periductal mastitis and idiopathic granulomatous mastitis (IGM). Lactational mastitis is most commonly caused by Staphylococcus aureus that is introduced into the breast milk during breastfeeding. The etiology of non-lactational mastitis is poorly understood, but periductal mastitis is commonly associated with smoking, and IGM is frequently associated with Corynebacterium. Patients present with edema, erythema, tenderness, and, possibly, a mass in the breast. Diagnosis is usually clinical, although ultrasound, cultures, and biopsy may be required in some cases. Management involves antibiotics, analgesics, drainage of any abscesses, and surgical duct excision for periductal mastitis.

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Mastitis refers to inflammation of the breast that may or may not be associated with infection.


  • Lactational mastitis (most common)
  • Non-lactational mastitis:
    • Periductal mastitis:
      • Inflammation of subareolar breast ducts
      • Different from mammary ductal ectasia, which involves ductal dilation and primarily affects postmenopausal women
    • Idiopathic granulomatous mastitis (IGM): peripheral inflammatory breast mass


  • Lactational mastitis:
    • Affects up to 10% of breastfeeding mothers
    • Most common in the first 3 months of lactation
  • Non-lactational mastitis:
    • Periductal mastitis: 
      • Most common in young women
      • Associated with smoking
    • IGM: 
      • Rare
      • Most common in young, multiparous women
      • Can occur in nulliparous women and men
      • In the United States, associated with Hispanic ethnicity

Etiology and Pathophysiology

Lactational mastitis

  • Most commonly associated with staphylococcal infection
  • Poor milk drainage leads to milk stasis and growth of microorganisms.
  • Pathogens: 
    • Enter milk ducts during breastfeeding (breast milk is not sterile)
    • Usually come from mother’s skin or infant’s mouth/nose
    • Most common infectious agents:
      • Staphylococcus aureus (most common); may be methicillin-resistant S. aureus (MRSA)
      • Group A or B Streptococcus
      • Escherichia coli
      • Corynebacterium
      • Bacteroides
  • Poor milk drainage or engorgement may result from:
    • Oversupply of milk
    • Infrequent feedings/pumping
    • Rapid weaning
    • Partial blockage of a duct
  • Additional risk factors:
    • Cracked nipples/excoriation
    • Illness in the mother or baby
    • Mother’s stress and fatigue
    • Depressed maternal immunity:
      • Human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS)
      • Diabetes mellitus
      • Cancer

Non-lactational mastitis

Periductal mastitis:

  • Inflammation of the subareolar ducts
  • Associated with smoking
  • Exact etiology is unknown; possibilities include:
    • Smoking, which damages subareolar ducts directly or through localized hypoxia
    • Squamous metaplasia associated with mastitis → partial duct blockage
    • Pathogenic organisms; isolated in 60%–85% of cases
    • Pathogens include:
      • Staphylococci (most common)
      • Enterococci
      • Bacteroides
      • Proteus


  • Peripheral inflammatory breast mass
  • Usually unilateral
  • No association with breast cancer
  • Etiology is unknown.
  • Associated with Corynebacterium (although unclear if causative)

Clinical Presentation


  • Mastitis presents with edema and erythema over the affected area. 
  • Abscesses may develop and present as tender, fluctuant masses.

Lactational mastitis

  • Edema, erythema, and warmth
  • Usually unilateral
  • Systemic symptoms of infection:
    • Fever/chills
    • Fatigue/general malaise
    • Myalgias (muscle aches) 
  • Pain during breastfeeding
  • Regional lymphadenopathy (tender and enlarged lymph nodes)
  • Fluctuant, tender mass (abscess in 3%–11% of cases)
Lactational mastitis

Lactational mastitis presents as an edematous and erythematous breast.

Image: “atlasofclinicals00bock” by Internet Archive Book Images. License: Public Domain

Periductal mastitis

  • Periareolar inflammation
  • Nipple discharge
  • Fluctuant, tender mass (abscess); can rupture and drain at the edge of areola
  • Draining cutaneous fistula (from chronic/recurrent abscess)


  • Peripheral inflammatory breast mass
  • May also develop:
    • Multiple areas of peripheral infection
    • Multiple small abscesses
    • Overlying skin ulcers 
  • Often mimics breast cancer:
    • Peau d’orange of the overlying skin
    • Axillary lymphadenopathy
    • Nipple retraction
IGM of the right breast

Idiopathic granulomatous mastitis (status post-incisional breast biopsy)

Image: “IGM of the right breast” by Dept. of Radiation Oncology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA. License: CC BY 2.0


Lactating mothers

  • Diagnosis is established based on clinical presentation.
  • Supportive studies:
    • Gram stain and culture of the milk:
      • Can help identify the causative organisms 
      • Only required in cases refractory to treatment
    • Blood culture: for severe progressive infection/signs of sepsis
    • Ultrasound:
      • To look for abscess → appears as a fluid-filled mass
      • If a mass is present on exam 
      • If there is no clinical improvement after 48–72 hours of empiric antibiotics
Abscess on ultrasound in diagnosis of mastitis

Ultrasound imaging of a breast abscess:
A: complex, with ill-defined borders
B: homogeneous in appearance with well-defined borders

Image: “Abscess” by Antônio Arildo Reginaldo de Holanda et al. License: CC BY 4.0

Non-lactating women

Periductal mastitis:

  • Diagnosis is based on clinical presentation.
  • Ultrasound can be obtained to rule out abscess.


  • Clinical presentation: may mimic breast cancer
  • Laboratory studies:
    • Gram stain and culture of any nipple discharge
    • Prolactin: may be ↑ in IGM 
  • Imaging:
    • Ultrasound:
      • Solid mass 
      • May also show single or multiple abscesses
    • Mammogram: may not be able to differentiate from malignancy
  • Core needle biopsy (CNB):
    • Biopsy suspicious masses found on ultrasound
    • Send for gram stain, culture, and histopathology.
    • IGM findings:
      • Non-caseating, non-necrotizing granulomatous inflammation
      • Negative for acid-fast bacilli or fungi
      • Cultures may grow Corynebacterium.


Lactational mastitis

  • Supportive care: 
    • Analgesics (nonsteroidal anti-inflammatory drugs, acetaminophen)
    • Cold compresses
    • Frequent, complete emptying of breast via:
      • Breastfeeding
      • Pumping
      • Hand expression
  • Antibiotics:
    • Non-MRSA: 
      • Antistaphylococcal penicillins: dicloxacillin
      • Cephalosporins: cephalexin
      • Erythromycin (beta-lactam hypersensitivity)
    • MRSA: 
      • Clindamycin 
      • Trimethoprim-sulfamethoxazole (avoid in mothers who are breastfeeding infants < 1 month old)
      • Intravenous vancomycin may be required for severe/septic presentation
  • Surgical therapy: incision and drainage of associated abscesses

Non-lactational mastitis

Periductal mastitis:

  • Often a chronic problem
  • Antibiotics:
    • Amoxicillin-clavulanate (1st line)
    • Trimethoprim-sulfamethoxazole if a concern for MRSA
    • Duration of treatment usually 5–7 days
  • Abscess:
    • Incision and drainage 
    • Needle aspiration
    • Will recur in up to 50% of cases
  • Fistulas and recurrent abscesses:
    • Surgical excision of involved ducts
    • Open or excise fistulous tract


  • Usually self-limiting and will resolve, but may take up to 20 months
  • Secondary infections treated with antibiotics and drainage of abscesses if necessary:
    • Empirically can be given same antibiotics as periductal mastitis
    • Adjust antibiotics based on culture and susceptibility.
    • Doxycycline for Corynebacterium 
  • Persistent and refractory IGM: Steroids and methotrexate can be used.

Differential Diagnosis

  • Inflammatory breast cancer: a rare, aggressive, rapidly growing breast cancer characterized by erythema and edema. Almost all women have lymph node involvement and up to ⅓ of women will have distant metastases upon presentation. The diagnosis should be suspected in women with rapidly progressive inflammation without improvement after antibiotics. Breast imaging with a diagnostic mammogram and ultrasound along with a CNB can confirm the diagnosis. Treatment involves surgery, chemotherapy, and radiation.
  • Breast abscess: the accumulation of pus within the mammary gland that is usually associated with mastitis. Presents as a unilateral and fluctuant mass within a painful, erythematous, and edematous breast. Treatment involves incision and drainage.
  • Galactocele: a cystic collection of fluid usually caused by an obstructed milk duct. Galactoceles present as a palpable, firm mass in the subareolar region and may show a classic fat-fluid level on imaging. Unlike lactational mastitis, galactoceles are not associated with systemic symptoms such as fever, malaise, or myalgias. Diagnosis is based on history and aspiration, yielding milky fluid. These lesions do not require excision.
  • Mammary duct ectasia: dilation of the subareolar ducts associated with fibrosis and thick, creamy nipple discharge. Previously considered part of the same syndrome as periductal mastitis, mammary duct ectasia is now considered to be an age-related phenomenon that is not associated with significant inflammation or infection. Ectasia typically occurs in postmenopausal women, while periductal mastitis usually occurs in younger women, especially those who smoke.


  1. Al-Khaffaf B., Knox F., Bundred N.J. (2008). Idiopathic granulomatous mastitis: a 25-year experience.J Am Coll Surg. 2008;206(2):269. 
  2. Ammari F.F., Yaghan R.J., Omari A.K. (2002). Periductal mastitis. Clinical characteristics and outcome. Saudi Med J. 2002;23(7):819. 
  3. Beckmann C.R.B., Ling, F.W., et al. (Eds.). Obstetric and Gynecology (6th Ed., p. 127).
  4. Dixon, J. M. (2020). Lactational mastitis. In Baron, E. L., and Eckler, K. (Eds.), UpToDate. Retrieved 1 February 2021, from
  5. Dixon, J. M., Pariser, K. M. (2020). Nonlactational mastitis in adults. In Baron, E. L., and Eckler, K. (Eds.), UpToDate. Retrieved 1 February 2021, from
  6. Schoenfeld E.M., McKay M.P. (2009). Mastitis and methicillin-resistant Staphylococcus aureus (MRSA): the calm before the storm? J Emerg Med. 2010;38(4):e31. Epub 2009 Feb 20.

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