Breast Abscess

A breast abscess is a collection of pus within an area of the breast, usually caused by a bacterial infection. This may be a:

  • Lactational abscess (associated with breastfeeding) 
  • Non-lactational abscess (unrelated to breastfeeding)


Pus is a thick fluid produced by inflammation. It contains dead white blood cells of the immune system and other waste from the fight against the infection. When pus becomes trapped in a specific area and cannot drain, an abscess will form and gradually increase in size.

Mastitis refers to inflammation of breast tissue. Often this is related to breastfeeding (lactational mastitis), although it can be caused by infection. Bacteria can enter at the nipple and back-track into the ducts, causing infection and inflammation. Mastitis caused by infection may precede the development of an abscess.

Smoking is a key risk factor for infective mastitis and breast abscesses. Damage to the nipple (e.g., nipple eczema, candidal infection or piercings) provides bacteria entry. Underlying breast disease (e.g., cancer) can affect the drainage of the breast, predisposing to infection.



The most common causative bacteria are:

  • Staphylococcus aureus (the most common)
  • Streptococcal species
  • Enterococcal species
  • Anaerobic bacteria (such as Bacteroides species and anaerobic streptococci)


TOM TIP: It is worth becoming familiar with the effective antibiotics against different classes of bacteria. Staph aureus, streptococcal and enterococcal bacteria are gram positive, meaning that penicillins are likely to be effective. Flucloxacillin, in particular, is used against staph aureus skin infections (this association is worth remembering). However, anaerobic bacteria can also cause breast abscesses, and simple penicillins (e.g., amoxicillin or flucloxacillin) do not cover anaerobic bacteria. Co-amoxiclav (amoxicillin plus clavulanic acid) covers anaerobes. Metronidazole gives excellent anaerobic cover (also worth remembering), so it can also be added to the mix. 



The presentation of mastitis or breast abscesses is usually acute, meaning the onset is within a few days. 

Mastitis with infection in the breast tissue presents with breast changes of:

  • Nipple changes
  • Purulent nipple discharge (pus from the nipple)
  • Localised pain
  • Tenderness
  • Warmth
  • Erythema (redness) 
  • Hardening of the skin or breast tissue
  • Swelling


The key feature that suggests a breast abscess is a swollen, fluctuant, tender lump within the breast. Fluctuance refers to being able to move fluid around within the lump using pressure during palpation. Where there is infection without an abscess, there can still be hardness of the tissue, forming a lump, but it will not be fluctuant as it is not filled with fluid.

There may be generalised symptoms of infection, such as:

  • Muscle aches
  • Fatigue
  • Fever
  • Signs of sepsis (e.g., tachycardia, raised respiratory rate and confusion)



The diagnosis of mastitis or a breast abscess can usually be made clinically, with a history and examination.

The NICE clinical knowledge summaries (last updated January 2021) recommend different management for mastitis depending on whether it is lactational or non-lactational. 


Lactational mastitis caused by blockage of the ducts is managed conservatively, with continued breastfeeding, expressing milk and breast massage. Heat packs, warm showers and simple analgesia can help symptoms. Antibiotics (flucloxacillin or erythromycin/clarithromycin where there is penicillin allergy) are required where infection is suspected or symptoms do not improve.


Management of non-lactational mastitis involves:

  • Analgesia
  • Antibiotics
  • Treatment for the underlying cause (e.g., eczema or candidal infection)


Antibiotics for non-lactational mastitis need to be broad-spectrum. The NICE clinical knowledge summaries (last updated January 2021) recommend either:

  • Co-amoxiclav
  • Erythromycin/clarithromycin (macrolides) plus metronidazole (to cover anaerobes)


Management of a breast abscess requires: 

  • Referral to the on-call surgical team in the hospital for management
  • Antibiotics
  • Ultrasound (confirm the diagnosis and exclude other pathology)
  • Drainage (needle aspiration or surgical incision and drainage)
  • Microscopy, culture and sensitivities of the drained fluid


Women who are breastfeeding are advised to continue breastfeeding when they have mastitis or breast abscesses. They should regularly express breast milk if feeding is too painful, then resume feeding when possible. This is not harmful to the baby and is important in helping resolve the mastitis or abscess.


Last updated June 2021
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