Can donated breastmilk be reused?

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With proper care and timely use, donated breastmilk can be reused as follows:

Fresh milk
Regarding raw and fresh milk, Lawrence writes: “Breastmilk can safely stand at room temperature for 6 to 8 hours and need not be discarded if the first feeding attempt is incomplete.”1

After feeding
Regarding reusing milk after a feeding, Dr. Ruth Lawrence writes: “Whether you can use the remaining milk really depends on how long it sits around. Once the baby takes the bottle, there is a certain amount of saliva that gets in the bottle that creates bacteria and gets saliva enzymes in the milk. This is why it isn’t good to give milk that has been sitting around. But, if it sits for only a half hour or so, this is fine.”2 There can be confusion as to what ‘sits around’ means. Eats on Feets assumes that in this context ‘sits around’ means ‘stand at room temperature.’

See ‘How do I feed the milk to my baby?’ for cleaner and thus safer feeding options.

After refrigeration
For raw and fresh (not frozen) breastmilk after refrigeration, this summary states: “[…] When infants do not finish a bottle of expressed breastmilk, doctors recommend unfinished portions be thrown away. This [small –ed.] study examined bacterial levels in expressed, partially consumed breastmilk that was stored for 48 hours at 4-6° C [bold –ed.]. A portion of unconsumed milk was examined as a control. Samples were taken every 12 hours for bacterial analysis. Tests were performed to identify total colony counts, pathogenic Staphylococci, coliforms and b-hemolytic Streptococci. This study showed no significant difference between bottles that were partially consumed and those that were not exposed to the baby’s mouth for 5 out of 6 participants. All milk samples had colony counts in the acceptable range of < 105 colony forming units per milliliter (CFU/ml). Although this project provides evidence that it may be safe to re-feed a child a bottle of breastmilk, due to the small sample size, further tests should be performed.”3

Most parents reheat leftover and refrigerated milk. Dr. Ruth Lawrence writes: “If the milk is warmed up but not used, it is OK to reheat the milk once. But the more you reheat the more you decrease some of the valuable immunologic properties of the milk.”

After freezing
Regarding previously frozen raw milk, it is generally accepted that thawed milk can be kept in the refrigerator for up to 24 hours. According to the USDA, “Once food is thawed in the refrigerator, it is safe to refreeze it without cooking.” In this protocol, Dr. Anne Eglash,M.D. writes: “At this time, there is little information on refreezing of thawed [fresh –ed.] human milk. Bacterial growth and loss of antibacterial activity in thawed milk will vary depending on the technique of milk thawing, duration of the thaw, and the amount of bacteria in the milk at the time of expression. At this time no recommendations can be made on the refreezing of thawed human milk.”

Please see ‘How can breastmilk be thawed?’ for thawing instructions. Most parents reheat (warm) previously frozen raw milk as well (after a first feeding). There is no research on whether this practice is safe or not.

Breastmilk that was frozen can be re-frozen after it has been heat-treated as well. This is the process that milk banks follow: frozen donated breastmilk is pasteurized, after which it is stored in the freezer.

Reusing heat-treated milk4

In this study, the researchers discuss that after cooling “flash-heat was successful in completely eliminating bacteria in the majority of samples, and prevented substantial growth for up to 8 h when stored at room temperature.”5

To date, the safety of reheating previously heat-treated milk has not, to our knowledge, been studied. It should be noted that most literature speaks in terms of heating expressed milk for feeding but that parents and caretakers generally warm the (thawed) milk under running warm water or set it in a container in warm water for a short while to get the chill out of it. Gently warming should not be considered heat-treating. For optimal properties of breastmilk, reheating (warming) milk should not be done directly in a pan on the stove top nor in a container in boiling water on the stove top (which would be heat-treating it unnecessarily). It is suggested however that after a first feeding, milk that was heat-treated not be refrigerated and reheated again.

Next: How do I clean or sterilize supplies and pump parts?


  1. Lawrence, Ruth. Breastfeeding, A Guide for the Medical Profession. P. 438. 2005. Print. []
  2. Using alternative feeding options to a bottle and/or using small amounts at a time avoids waste and contamination. []
  3. Brusseau, R. “Bacterial Analysis of Refrigerated Human Milk Following Infant Feeding.” May 1998. Web. []
  4. This can be the case if a donor heat-treats the milk because of high lipase or after a recipient heat-treats the milk and there is milk left over after a feeding for instance. []
  5. Per the same study “Flash-heated and unheated samples were stored at 2–8oC [35oF–46oF –ed.] overnight to be processed for microbiology assays the next morning, 18–24 h after collection. At this time, both flash-heated and unheated aliquots were placed at room temperature (23C) [73oF –ed.] and allowed to stand, in capped vials, for up to 8 h.” []

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