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How Long Does Breast Milk Last After Warming?

How long is warmed breast milk good for? If you pump for your little one then this is vital information to know – especially if you’re also an allergy mama! Find out how best to store your milk and keep your baby safe.

Why It’s So Important to Know How Long Warmed Breast Milk is Good For

How long does breast milk stay good? | Image shows a double breast pump containing expressed milk with a stash of bags of milk behind it. There's a sleeping baby in the background.
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If you’re breastfeeding and you also express for your infant, you’ll know that it’s quite the commitment! Pumping can be uncomfortable and time-consuming, and therefore every single drop of that liquid gold counts. But sometimes offering a bottle of breast milk is necessary, whether that’s because you work or simply so you can get a break.

If you’re also following a dairy free diet or similar to eliminate allergens for your baby, and you have to be away from them, your expressed milk is vital for your baby’s care and it’s even more important that none is wasted.

With this in mind it’s really important to understand the following:

  • How long does breast milk stay good in different circumstances (fresh / refrigerated / thawed etc)?
  • How long does breast milk last after warming?
  • How long is breast milk good in the fridge?
  • How long can you store breast milk in the freezer?
  • Can you save breast milk after it has been heated?
  • How to thaw breast milk.
How long is warmed breast milk good for? | Image shows a stash of bags of expressed milk beside a soft bunny with a blue hat and a baby bottle containing milk.

So, what are the guidelines for ensuring your milk is stored effectively, prolonging its life and nutritional content? Here’s everything you need to know for safely maximising how long your breast milk is good for, without compromising your baby’s immune system.

Read more: Can you use breast milk for baby acne or sticky eyes?

Human Milk Storage Information For How to Safely Store Breast Milk

The very best way to maximise how long you can safely use your stash of expressed milk for, is to practice fastidious sanitation at the time of expressing and during the storage process. Here’s how:

  1. Sanitation
  • This goes without saying really, but it’s critical to keep your electric pump and bottles immaculate. 
  • Before you start wash your hands with soap and water, or if there’s none available use alcohol hand gel.
  • Avoid sharing a breast pump with anyone else and ensure all dials and tubing are thoroughly disinfected.
Image shows a row of bottles and dummies / pacifiers lined up on a tea towel next to a sink.
  • Bottles should be properly clean before pumping. Wash them with soap and hot water and allow them to air dry completely or use a clean tea towel.
  1. Choice of Milk Containers

The containers you use for storing your breast milk are important and should be made from BPA-free materials. This is because the long-term effects of the chemical, which is often found in plastic containers and coatings, are unknown.

Choose properly cleaned baby bottles or use breast milk storage bags which are designed specifically for the purpose.

  1. Storage Time

Finally, follow the time guidelines (below) for safe storage of your breast milk at room temperature, in the fridge, freezer, or once thawed/warmed.

Need a breast pump? I loved this one:

General Guidelines for How to Store Breast Milk at Room Temperature

Follow these guidelines for optimal room temperature breast milk storage:

Image shows a breast pump next to a baby bottle. There's a mirror and a plant in the background.
  • Keep your breastmilk away from heat sources such as radiators.
  • Keep out of direct sunlight.
  • Keep bottles or storage bags sealed.

How to Store Breast Milk in the Fridge

Follow these guidelines for optimal breast milk storage in the refrigerator:

  • After expressing, place fresh breast milk in the fridge for later use as soon as possible.
  • It’s fine to add freshly expressed milk to a container of previously refrigerated milk, however you should ensure the new milk is thoroughly cooled first. Don’t add warm / body temperature breast milk to frozen milk as it will cause the frozen milk to partially thaw.
  • Avoid leaving your milk in the fridge door which has the least consistent temperature. Choose the coldest area instead, which is usually at the back of the refrigerator.

How to Store Breast Milk in the Freezer

Follow these guidelines for optimal breast milk storage in the freezer:

  • Freeze your breast milk as soon as possible after expressing.
  • It’s fine to add thoroughly cooled breast milk to a bag of previously frozen milk. Do not add warm or room temperature breast milk to frozen milk.
  • As with the refrigerator, store breast milk at the back of the freezer where the temperature tends to be more consistent. If you have a self-defrosting freezer, don’t allow your breastmilk to touch the walls.
  • Store breast milk in portions of 2 – 3 ounces to minimise wastage. These can easily be combined upon thawing if required.
How long can you store breast Milk? | Image shows a woman holding a frozen bag of breast milk, with a stash in the background.
  • Check your storage containers are safe for use in the freezer, as materials such as glass may crack at certain temperatures.
  • Ensure containers are not over-filled – liquids including breast milk expand during the freezing process. Leave a gap of around an inch to allow for expansion. 

How Long Can Expressed Breast Milk Be Stored For?

At the time of researching this post, depending on which official guidelines you refer to, you’ll find slightly varying answers to this question. 

Based on recommendations by the CDC, AAP, and NHS, it’s sensible to assume there’s a safe window of time that breast milk can be stored for.

When sanitation and temperature consistency have been meticulous at the time of expressing and during storage, it’s safe to go by the longer recommendation; otherwise to err on the side of caution you may prefer to go by the shorter guidelines.

  • Fresh breastmilk can be kept at room temperature (77°F / 25°C) for 4 – 8 hours.
  • Storage in a refrigerator with a temperature of around 4°C is okay up to a maximum of 8 days. Most places online show 3 – 6 days, however 8 is okay according to this study. That said, it’s preferable to freeze milk if you won’t use it within 4 days, during which time it’s at its best.
  • Storage of breast milk in the freezer should be at less than -4°C (24.8°F), for up to 6 – 12 months.
  • Thawed breast milk can be kept at room temperature for a maximum of 2 hours, or in the refrigerator for 24 hours. Source.
  • Breast milk can be stored in an insulated cooler bag with ice packs, at an equivalent temperature of 15°C (59°F) for 24 hours if you’re travelling, based on this study. Milk should be used, refrigerated, or frozen as soon as possible.
  • Further research would be helpful for better understanding safety measures for thawed, previously fed leftover milk. However, at this time and given the insufficient research, recommendations are to discard thawed, leftover breast milk within 1 – 2 hours due to potential contamination. Source.
  • Again, there’s insufficient research available with reference to refreezing thawed breast milk, and with that in mind it is currently advised against.

Breast Milk Storage Guidelines

Keep in mind that the benefits of breast milk deteriorate over time.

How to Safely Warm Breast Milk 

Follow these guidelines for how to thaw breast milk safely:

  1. Over time, your milk’s nutritional quality and antibacterial properties begin to degrade. For this reason, rotate breast milk accordingly by thawing and using your oldest breast milk first.
  1. Frozen breast milk can safely be thawed either by refrigerating overnight, running under lukewarm water, using a bottle warmer, or submerging in a container of lukewarm water. Refrigerating overnight allows for maximum life once thawed.
How to thaw breast milk. | Image shows a bottle of milk in a bottle warmer.
  1. Use breast milk thawed to room temperature or warmed within 2 hours.
  1. Once breast milk is thawed, its ability to inhibit bacterial growth lessens. Breastmilk should be used within 24 hours after thawing in the fridge (from the time it is completely thawed.)
  1. Never heat breast milk in the microwave; studies show it significantly decreases the immunologic activity of the milk, reducing the benefit to your infant. Microwave ovens are also notorious for causing hot spots during heating, which pose a risk of burns to your baby’s mouth.
  1. Do not refreeze thawed breast milk.

How Long is Warmed Breast Milk Good For?

How long does warmed breast milk last if you follow recommendations? Follow these guidelines to keep your baby safe and healthy:

  • Thawed breast milk should be discarded after 2 hours at room temperature. 
  • Thawed breast milk can be given straight from the fridge or at room temperature, if your infant will accept it – warm milk is only necessary if they demand it!
  • Keep the container closed during warming, should you choose to do so. Check the temperature on your arm before feeding to your baby.
Image shows expressed breastmilk with mother nursing baby in the background.

Tips For Storing Expressed Breast Milk

Here are a few additional tips to help you properly care for your expressed milk:

  1. Clearly label your expressed milk with the date.
  1. Freeze expressed milk in small amounts of 2 – 4 ounce portions.
  1. Don’t store breast milk in the fridge door where temperatures are inconsistent.
  1. If you don’t expect to use breast milk within four days, freeze it as soon as possible to retain its nutritional and immunological properties at their best.
  1. Leave an inch of space at the top of your storage container when you freeze breastmilk.
  1. Clearly label milk with your baby’s name for your child care provider.
  1. Familiarise yourself with what high lipase milk is (tell-tale signs are a metallic or soapy smell) and, if necessary, scald your milk prior to freezing!

Tips For Preventing Wasted Expressed Breast Milk

Try these tips to reduce wastage of expressed breast milk:

1. Don’t heat milk until the last moment.

Avoiding defrosting breast milk until you are absolutely certain you need is a good idea, just in case you’re around after all and can nurse yourself.

2. Freeze and defrost in small quantities.

Thawing smaller amounts means that if baby doesn’t want a great deal of milk, there won’t be lots of waste.

3. Defrost in the fridge.

Defrosting in the fridge also helps to keep your expressed milk fresh for longer.

4. Try baby with cold milk.

You don’t have to warm your baby’s milk if they’ll accept cooler!

5. Before building up stash of expressed milk, check you don’t produce high lipase milk which your infant may refuse!

This occurs only after milk has sat for a while or been frozen, so you wouldn’t be aware of it from when your infant nurses straight from the breast.


How to Tell If Breast Milk is Bad

The above information gives clear guidelines to help prevent your milk spoiling before offering it your baby. But how can you check if you’re concerned your milk has gone bad?

1. Do the sniff test – just like with regular milk, if the milk smells sour, it’s likely spoiled.

2. If milk has separated this does not necessarily mean it’s bad. 

If you’ve ever seen expressed milk you’ll already know that it does tend to separate, and this is completely normal. However, it should mix back together with a swirl or shake. 

If you find your milk appears lumpy and resistant to mixing back together, it may well have spoiled.

This guidance is designed for full-term babies. For further advice, especially for early babies, reach out to your health care provider or lactation consultant.