Reheating Breast Milk: Important Safety Guidelines To Follow

| Reviewed By Sarah Schulze, MSN, APRN, CPNP

If you are a new mother, you may have many questions regarding breast milk. A common concern is what to do with pumped milk leftover in a bottle. Can it be reheated safely? Or should it be thrown out instead?

Can you reheat breast milk more than once? There are many different opinions and experiences, but the CDC advises against reheating breast milk more than once. Doing so inactivates and denatures valuable proteins and fat content in the breast milk. Rather than reheating or discarding unused milk, save it for a milk bath!

There is so much to learn when it comes to storing, serving, and warming breast milk. Let’s break it down a little bit so that you can feel confident in what is best for your baby! 

Reheating Breast Milk: Full Guide

Many mothers will choose to freeze or refrigerate pumped breast milk for later use — perhaps for when they need a bottle on the go or for a time when they would like someone else to give their baby a bottle. 

It is also a great option for those mothers who pump exclusively or have an oversupply. 

The only downside is trying to figure out how to warm the milk for your baby. Let’s look at some research and figure out the best way to get the bottle nice and warm for your little one. 

How To Warm Refrigerated Breast Milk

These are the CDC guidelines for warming refrigerated breast milk: 

  • Fill the bottle with breast milk, and make sure it is closed tightly.
  • Run the bottle under cool running water. Gradually add warm (not hot) water until the bottle reaches room temperature. You might also place it in a bowl of warm water, but do not place it in water on the stove. 
  • Swirl the breast milk to mix the fat, which may have been separated.  
  • Test the milk’s temperature on your finger before serving it to your baby. 

Can You Reheat Breast Milk Twice?

What if your baby doesn’t finish the warm bottle and it cools off? Are you able to reheat it? 

Per the CDC, once you have heated stored breast milk once, any milk remaining in the bottle two hours after a feed should be discarded and not reheated or stored for later use. 

I know pouring your liquid gold down the drain can be disheartening. As an exclusive pumper myself, I hated seeing any of my milk go to waste.

Instead of discarding my milk, I would save it for a milk bath later that evening or use it on my baby’s skin to treat small rashes or eczema. 

Why Reheating Breast Milk Is Not Recommended

The main reason for not reheating breast milk is because of the effects high temperatures have on the composition and nutritional components of breast milk. 

Breast milk is a living fluid full of immune-boosting and bacteria-fighting properties.

It is packed with antibodies, bioactive components such as hormones and enzymes, and living cells to help support the growth and development of your baby. 

High temperatures kill or damage these living components that make breast milk so beneficial for babies. When breast milk is exposed to heat through multiple heating processes, it loses more of its nutritional benefit each time. 

How Many Times Can You Reheat Unused Breast Milk?

Let’s say your baby didn’t finish her bottle, but it still hasn’t been two hours. Can you reheat it? 

The results of a survey of moms of healthy babies show that nearly 50% of mothers will reheat unused breast milk. Is it recommended? No. 

What Happens if You Heat Breast Milk Too Much?

High temperatures destroy cells. Breast milk is full of living components (antibodies, enzymes, bioactive proteins, etc.) that your baby needs.

Exposing breast milk to high temperatures multiple times destroys these valuable immunological components. Overheating also destroys the fat content of breast milk that your baby needs to grow and thrive. 

Does Warming Breast Milk Destroy Antibodies?

Oh, those wonderful antibodies. They are one of the main reasons breast milk is so beneficial! It is like a built-in immunity-defense system for your baby. 

According to La Leche League, exposing breast milk to high temperatures can decrease its anti-infective properties. In other words, heat kills antibodies. 

Does Breast Milk Lose Nutrients When Heated?

One study discovered that when human milk is exposed to temperatures higher than 104 degrees Fahrenheit, its nutritional and immunological value begins to deteriorate.

Tap water can get as hot as 160℉! So, be careful when warming your little one’s bottle. Be sure to use warm or room-temperature water.

Even though it may take a little longer to warm up, it is worth waiting a few extra moments for a nutrient-rich bottle of breastmilk. 

Once Breast Milk Is Heated, Can It Be Refrigerated?

If you give your baby a warmed bottle of breastmilk and she does not finish it, you may refrigerate it and offer it again (cold) within two hours of the initial warming.

Can You Microwave Breast Milk?

This is another heavily debated topic. I’m sure there are plenty of moms out there that use the microwave to warm bottles (I, myself, am guilty of doing so when I am in a pinch).

However, the CDC advises against using the microwave to heat expressed breast milk.

Why? First, the temperature of a microwave gets extremely high and surely kills many valuable nutrients. Also, the microwave does not distribute the heat evenly, and there may be hot pockets in the bottle that can burn your baby’s mouth. 

So, as I said, I’m sure there are people who do it. Will it kill your baby or make her sick if she has a bottle that was warmed in the microwave? No, but it is not recommended for optimal safety and nutrition purposes.

Your baby will not be getting all of the rich nutrients from the breast milk that she would be getting if you warmed it a different way. 

How Long Can Warmed Breast Milk Stay Out?

The rule of thumb is that breast milk that has been thawed or warmed up can remain at room temperature for two hours. 

Can Breast Milk Be Given Straight From the Fridge?

Cold breast milk is perfectly healthy for babies. In fact, by not warming the breast milk, you are preserving some of the nutrients!

If you are fortunate enough to have a baby who will drink cold milk, you can certainly give her a bottle straight from the fridge. 

How To Use Refrigerated Breast Milk

Okay, so you’ve decided that you’re going to give this pumping and storing thing a try. But how do you store the milk? What is safe and unsafe? Let’s unpack these questions. 

A cute baby girl being held while she drinks her bottle.

Tips for Establishing a System

There are a few different systems for storing and feeding stored breast milk. 

Pitcher Method

This system is great for exclusive pumpers. Basically, you put all of your pumped milk from one day into large mason jars with pour spouts.

You will use this milk the next day to feed your baby. You basically pump ahead for the next day while your baby drinks the milk that you pumped the previous day. 

Whatever is left over in the pitcher at the end of the day goes into bags to be frozen or used in milk baths. 

Nursing and Pumping Combination

There are plenty of mothers who both nurse and pump. This helps with oversupply and/or in building a freezer stash for days away from your baby. 

Some mothers will pump early in the morning, nurse throughout the day, and then pump again at night.

This is a great way to build a freezer stash or have milk in the fridge to use in bottles when you are unable to nurse. Just be sure to use whatever milk you store in the refrigerator within 4 days. 

Labeling Bags and Bottles 

Labeling storage bags or bottles is extremely important. This is key to knowing how long your milk has been in the fridge or freezer. 

  • Write the date of when the milk was expressed.
  • Write the amount (measure in bottles before pouring into the bag).
  • Leave enough room at the top of the bag or bottle for milk to expand when frozen.

Storage Times

Refrigerator, freezer, or counter? Milk has different storage times depending on where it is stored. Freshly pumped or expressed milk can be stored: 

  • At room temperature for up to four hours.
  • In the refrigerator for up to four days.
  • In the freezer for up to one year. Using it within 6 months is preferred. 
  • Frozen milk can be moved to the refrigerator to thaw, but it must be used within 24 hours after it is completely thawed. 
  • Once heated, milk must be consumed within 2 hours. 

Related Questions: 

Can You Defrost Breast Milk in the Microwave?

Breast milk should really never be put in the microwave. The best method for defrosting breast milk is to use warm water or place the frozen milk in the refrigerator for a few hours. 

Does Microwaving Breast Milk Destroy Nutrients?

Any form of extreme heat used to warm breast milk will destroy nutrients. That includes using the microwave. 

Final Thoughts

Breastfeeding, whether through nursing or pumping, is no easy feat! It takes a lot of time and commitment.

Keeping up with all of the safety regulations can be a bit of a headache. So, way to go, Mama! You’re amazing. We hope this information gives you a bit of guidance and helps you in your breastfeeding journey.