Breastmilk, Formula, and Combined Milk Storage Guidelines to Keep Your Baby Safe

breastfeeding combo-feeding formula newborn preparing formula Dec 01, 2022
A dad safely feeds his baby a bottle of breastmilk prepared with safe storage guidelines. This is important for safe bottle feeding and keeping babies healthy.

There are so many questions about feeding your baby. One that we do not get enough education on is about safe storage of breastmilk, formula, and combined milk.

I remember painstakingly collecting breastmilk after each nursing session. I would carefully pour the few milliliters into a freezer bag thinking that there HAD to be a better way.

Cue the frantic googling of breastmilk storage guidelines.

Now I know that keeping breastmilk in the fridge is a-okay, but storage guidelines are important to understand because we, of course, want to keep our babies as safe as possible.

Safe storage of formula, breastmilk, and combined milk can help prevent diarrhea, bacterial infections, gas, and stomach discomfort.

See! SO important.

Let’s break this down to make it easier to understand.


Did you know that how much milk is expressed, the temperature of the room, the temperature variance in the fridge or freezer, and how clean the environment is can all impact how long breastmilk can be safely stored?

Here are the CDC guidelines for storage:

  • Freshly expressed milk:
    • Room Temp: breast milk can be safely stored on the counter for up to 4 hours.
    • Fridge: Up to 4 days.
    • Frozen: It is best used within 6 months but should not be used after 12 months.
      • Pro tip: store in the back of the freezer where the temperature doesn’t fluctuate as much.
  • Thawed or previously frozen breast milk:
    • Room temperature: it should be used within 1-2 hours after the last milk crystal has melted.
    • Fridge: Up to 24 hours after the last milk crystal has melted.
    • Frozen: Never re-freeze milk after it has been thawed.
  • Leftover milk from a feeding: No matter what, use it within 2 hours after the feeding started. 

For reference, when I state room temp, fridge, or freezer, these are the recommended temperatures:

  • room temperature: 77 degrees or cooler

  • refrigerator: 40 degrees or cooler.

  • freezer: 0 degrees or colder.

Yes, that means that if your house is warmer than 77 degrees Fahrenheit, your milk will spoil faster.

Breastmilk Storage Tips:

  • First, always use milk storage bags or food-grade containers. Avoid using disposable bottle liners or plastic bags. They are not meant to store milk for extended periods of time and can leak or easily be contaminated.
  • Make sure to label the milk with the date it was expressed and store it in 2-4 oz increments to minimize waste (this also depends on how much your baby eats per feed). 
    • Remember, you can combine milk from different pumping sessions as long as it is the same temperature and not expired.
    • You can also store milk immediately after pumping.
  • If you have a childcare provider who will be feeding the milk to your child, make sure to label the milk with the child’s name to avoid any confusion. 


When preparing baby formula, the most important rule is to read and reread the instructions on the label! I can't tell you how many times parents believe they are mixing it correctly only to find out that is not the case. 

The CDC also has guidelines for proper baby formula storage:

  • Room Temp: Prepared formula should be used within 2 hours after it has been prepped.
  • Fridge: Up to 24 hours if your baby has not drunk from the bottle.
  • Freezer: NEVER freeze formula. Freezing can change the properties of the formula and make it unsafe for your baby. 

Formula tips:

  • Throw out any formula in the bottle your baby did not consume within one hour. The mixture of formula and the baby’s saliva can cause bacteria to grow.
  • Store unopened cans of formula in a cool, dry environment. Avoid places with large fluctuations in temperature and humidity (like most garages).
  • Opened cans of formula should be stored with the lid tightly secured and in a cool, dry environment (not the fridge). Opened cans of formula should be used within 1 month.
    • Pro tip: write the date on the lid when you open it so you know when it was opened and how long you have to use it.

If you are using ready-to-feed formula, follow the instructions on the bottle. They are usually good for about 24-48 hours in the fridge.

With any formula, follow the guidelines and never use it after the “Use by” date and throw out or return any cans with dents in them - it can compromise the seal, and bacteria can grow.

Combined Milk

Some parents may combine both breast milk and formula in the bottle.

Unfortunately, there are no official guidelines on how to properly store combined milk.

I recommend following formula guidelines, as bacteria grows quicker in formula than in breast milk.

You can also prepare the formula separately, and combine it with breastmilk before heating or serving.


Feeding your baby is one of the most basic yet complicated things you will do for your child. By following the storage guidelines outlined above, you can ensure your baby will be well-fed with a happy tummy.

If you have any questions about this or anything related to feeding your baby, please reach out to me. I’m happy to help.


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