Can you Reheat Unused Breast Milk More Than Once?

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As a first-time mother, you have many questions when it comes to an unfinished bottle of expressed breast milk. The most common question that moms have is, can you reheat unused breast milk more than once. Read on to get the answer to your question.

If you are a working mom or a mom who just started expressing breastmilk to get some flexibility in your breastfeeding routine, it is important to know how to safely handle expressed breast milk.

Proper handling of the expressed breast milk is important to preserve its nutrition and its immune-boosting properties. After all, it is the main source of nutrition for your baby’s first year of life.

can you reheat breast milk more than once

While I exclusively breastfeed my both babies, but a time came when I had to express breast milk to take a break from breastfeeding as I had a cut in my both nipples.

I have to admit, it was so much work to build a small stockpile of breast milk for that short duration of time until I was able to breastfeed again.

After pumping around the clock to keep up with milk supply, I wanted to save even a few MLS of breast milk if the baby did not finish a bottle.

It is when I started researching if I can reheat breast milk more than once if the baby didn’t finish the bottle.

The CDC guideline for breast milk handling suggests using leftover breast milk after feeding a baby within 2 hours but there was no guideline on reheating the unused breast milk.

When I started researching whether you can warm unused breast milk twice, I was surprised to know that there aren’t any research studies that investigated this question. Keep reading to find out if you can reheat breast milk more than once if the baby didn’t finish the bottle.

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Can you Reheat Unused Breast Milk More than Once?

The CDC guideline for handling breastmilk suggests using leftover breast milk after feeding within 2 hours.

The reason being bacteria enter the bottle from your baby’s mouth during feeding and will eventually spoil the milk. However, there is no evidence of how fast that happens.

I did a survey of moms of a healthy baby on a Facebook group asking them whether they have reheated unused breast milk more than once for feeding their babies. Out of 40, 25 moms answered ‘yes’.  

Breastmilk is full of immune-boosting, bacteria-fighting, digestion enhancing, and microbiome-building properties. No wonder why some mamas want to feed their baby the last drop of expressed breast milk!!

However, the quality and safety of reheated unused breast milk depend on several factors.

  • Cleanliness of your milk expression method will affect the number of bacteria present in the breast milk to begin with
  • way you warm the breast milk
  • Storage temperature and condition

According to the Academy of Breastfeeding Medicine clinical protocol (Revision 2017), the duration of time unused breast milk after feeding can stay at room temperature depends on the initial bacterial load in the breast milk, how long the breast milk has been thawed, and the ambient temperature(1).

As there are no studies to provide these recommendations, it is reasonable to discard unused breast milk within 2 hours after feeding a baby.

In addition to containing essential nutrients, breast milk is rich in numerous bioactive components such as hormones, growth factors, enzymes, and live cells to support the growth and development of the baby (2).

And the way you warm the breast milk affects the live component of breast milk.

A research study published in 2015 suggests that overheating breast milk (above 143º F) can destroy some of these essential nutrients and live cells (3-4).

You will be surprised to know that hot tap water temperature can reach 140º F. so, be careful if you are heating the breast milk under the running hot tap water!!

So, it is important to learn how to properly reheat breast milk to preserve all the nutrients in breast milk.

Overheating breast milk causes a marked decrease in anti-infective properties and fat content causes denaturation and inactivation of bioactive molecules in breast milk.

Lukewarm water between 98º and 105º F is enough to warm breast milk to body temperature.

The above indirect evidence suggests that overheating or exposing breast milk to repeated heat may cause denaturation of some essential bioactive molecule. And you don’t want to feed your baby suboptimal breast milk, right!!

Ideally, once refrigerated or frozen milk is thawed and warmed up to room temperature and once feed to the baby, it should be discarded within 2 hours.

Note: You should avoid feeding reheated unused breast milk to a Preemie or a sick infant with a compromised immune system. In these cases, discard any unused breast milk after feeding.

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Can Reheated Milk go Bad?

Unlike formula, breast milk can last longer once heated. But if storage guideline is not followed promptly it can go bad. Here are signs to watch out for

  • A Bad Smell: Spoiled breast milk has a distinct smell which is different from a soapy smell caused by higher lipase content of breast milk. Your baby might refuse to drink it, but this does not mean your breast milk is bad.
  • A Bad Taste: If you think milk breast has gone bad, taste it before offering it to your baby. If breast milk tastes sour, it has gone bad.
  • Separate layers of breast milk: Usually when you refrigerate breast milk, it separates into fat and non-fat layers. If your milk is good, two layers will combine upon mixing. But if breast milk has gone bad, you will notice chunk when mixing.

If you are not sure about the quality of your unused breast milk, it is better to toss it out than feeding your baby and making her sick!!

So, can you reheat unused breast milk more than once?

I would not reheat unused breast milk more than once. But if you want to reheat unused breast milk for feeding, make sure you are following proper breast milk handling and storage guidelines set out by CDC from the beginning.

Here is want you really need to do if you want to reheat unused breast milk more than once.

  • Immediately refrigerate leftover breast milk after the baby is done feeding. Refrigerating breast milk slowdowns bacterial growth.
  • For the next feeding session, reheat the breast milk by placing it in a bowl of warm water (not hot) for a few mins. Swirl the bottle gently to mix it.
  • Check or examine or taste the breast milk using the above tips to ensure it has not gone bad before feeding it to your baby.
  • Just remember that each time you reheat a bottle of breast milk, it will lose some of its bioactive molecules.
  • And when you are in doubt, throw it out.

But if you can avoid feeding reheated unused breast milk to your baby, avoid it by all means as it is not worth taking a risk especially when your baby’s immune system is still developing.

Personally, I would not feed unused, reheated breast milk to a baby younger than 3- months old.

And if you are hesitant to dump the unused precious breast milk, you really don’t have to dump it. There are many ways you can use unused or even expired breast milk other than feeding your baby.

One of the Facebook mamas used breast milk on her stretch marks and saw a very promising result. You can do the same with your leftover breast milk.

To get more idea read this article on ways to use unused breast milk or expired breast milk other than dumping.

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Can You Refrigerate Unused Breast Milk?

As mentioned earlier, heated or used breast milk should be used within 2 hours.

As there is no clear guideline about this, many moms keep unused breast milk at room temperature and others keep it refrigerated. There is no way to tell if one method is better than the other.

Though I do not recommend keeping unused breast milk after feeding the baby at room temperature especially when the room is hot, or you are traveling.  

Unused breast milk after feeding a baby is contaminated by the baby’s mouth and now it is the breeding ground of bacteria. Keeping it refrigerated will slow the growth of bacteria.

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How about you?

Have you reheated unused breast milk more than once? Leave your comment below!


  1. Anne Eglash, Liliana Simon, The Academy of Breastfeeding Medicine, Wendy Brodribb, Sarah Reece-Stremtan, Larry Noble, Nancy Brent, Maya Bunik, Cadey Harrel, Ruth A. Lawrence, Yvonne LeFort, Kathleen A. Marinelli, Casey Rosen-Carole, Susan Rothenberg, Tomoko Seo, Rose St. Fleur, and Michal Young.Breastfeeding Medicine.Sep 2017.390-395.
  2. Hamosh M. Bioactive factors in human milk. Pediatric Clinics. 2001;48(1):69-86.
  3. Bransburg-Zabary S, Virozub A, Mimouni FB. Human Milk Warming Temperatures Using a Simulation of Currently Available Storage and Warming Methods. PLoS One. 2015 Jun 10;10(6):e0128806. doi: 10.1371/journal.pone.0128806. Erratum in: PLoS One. 2016;11(2):e0148970. PMID: 26061694; PMCID: PMC4465021.
  4. Büttner BE, Witthöft CM, Domellöf M, Hernell O, Öhlund I. Effect of type of heat treatment of breastmilk on folate content and pattern. Breastfeed Med. 2014 Mar;9(2):86-91. doi: 10.1089/bfm.2013.0008. Epub 2013 Jun 20. PMID: 23786311.

Image baby drinking milk from a bottle – Photo by Lucy Wolski on Unsplash

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