Subacute mastitis

Why is my breast pain not getting better?

Breast pain can be temporary and caused by normal breastfeeding. A very small number of breastfeeding women have persistent breast pain with no identifiable cause. Some authors have described persistent breast pain as being caused by “subacute mastitis” and attributed this to an overgrowth of certain bacteria and a lack of other types in the breast and milk. Treatment recommendations have included antibiotics and probiotics.  

A) Subacute mastitis

It is normal for some mothers to have mild breast discomfort in the first few weeks after starting to breastfeed.

Some research suggests ongoing and more severe breast pain may be caused by an unhealthy breast microbiome: the overgrowth of certain bacteria and a lack of others in the milk ducts (Boix-Amorós 2020; Patel 2017; Jiménez 2015). This condition has been called subacute or subclinical mastitis or bacterial dysbiosis (Berens 2016; Jiménez 2017; Walker 2018). 

The affected breast is tender to touch and the pain has been reported to be:

  • With the let-down and after feeding or pumping.
  • Deep or penetrating.
  • Sharp or dull.
  • On one or both sides.

It is possible to test expressed breast milk to see which types of bacteria are present. Some clinicians suspect the following bacteria may cause subacute mastitis:  

  • Coagulase-negative staphylococci
  • Methicillin-resistant Staphylococcus aureus
  • Group B streptococcus
  • Streptococcus mitis

The overgrowth may cause inflammation and pain. In theory, inflammation may be the cause of plugged ductsAn unhealthy breast microbiome may have a role in the development of breast cancer (Parida 2019).

In addition to the types of bacteria present in the breast, mothers with subacute mastitis may have reactive changes in milk levels of sugar (lactose), minerals, protein, and higher levels of chemicals that cause inflammation (Samuel 2020; Tuaillon 2017). Their milk has been found to have a higher level of salt (sodium) to potassium (Samuel 2020).  

Subacute mastitis differs from typical mastitis in that there is no redness and no fever. Such mothers may have previously had mastitis.

It is unlikely this pain is caused by a nipple yeast infection (Kaski 2018).

Recommended treatments have included antibiotics by mouth and probiotics (Berens 2016; Eglash 2006; Espinosa-Martos 2016; Fernandez 2014).


Berens P, Eglash A, Malloy M, et al. ABM Clinical Protocol #26: Persistent Pain with Breastfeeding. Breastfeed Med. 2016 Mar;11(2):46-53

Boix-Amorós A, Hernández-Aguilar MT, Artacho A, et al. Human milk microbiota in sub-acute lactational mastitis induces inflammation and undergoes changes in composition, diversity and load. Sci Rep. 2020 Oct 28;10(1):18521
Eglash A, Plane MB, Mundt M. History, physical and laboratory findings, and clinical outcomes of lactating women treated with antibiotics for chronic breast and/or nipple pain. J Hum Lact. 2006 Nov;22(4):429-33
Espinosa-Martos I, Jiménez E, de Andrés J, et al. Milk and blood biomarkers associated to the clinical efficacy of a probiotic for the treatment of infectious mastitis. Benef Microbes. 2016 Jun;7(3):305-18
Fernández L, Arroyo R, Espinosa I, et al. Probiotics for human lactational mastitis. Benef Microbes 2014;5:169–183
Jiménez E, Arroyo R, Cárdenas N, et al. Mammary candidiasis: A medical condition without scientific evidence? PLoS One. 2017 Jul 13;12(7):e0181071
Jiménez E, de Andrés J, Manrique M, et al. Metagenomic Analysis of Milk of Healthy and Mastitis-Suffering Women. J Hum Lact. 2015 Aug;31(3):406-15
Kaski K, Kvist LJ. Deep breast pain during lactation: a case-control study in Sweden investigating the role of Candida albicans. Int Breastfeed J. 2018 Jun 7;13:21
Parida S, Sharma D. The power of small changes: Comprehensive analyses of microbial dysbiosis in breast cancer. Biochim Biophys Acta Rev Cancer. 2019 Apr;1871(2):392-405
Patel SH, Vaidya YH, Patel RJ, et al. Culture independent assessment of human milk microbial community in lactational mastitis. Sci Rep. 2017 Aug 10;7(1):7804

Samuel TM, De Castro CA, Dubascoux S, et al. Subclinical Mastitis in a European Multicenter Cohort: Prevalence, Impact on Human Milk (HM) Composition, and Association with Infant HM Intake and Growth. Nutrients. 2019 Dec 30;12(1):105

Tuaillon E, Viljoen J, Dujols P, et al. Subclinical mastitis occurs frequently in association with dramatic changes in inflammatory/anti-inflammatory breast milk components. Pediatr Res. 2017 Apr;81(4):556-564
Walker M. Mammary dysbiosis. Clinical Lactation 2018;9(3)