Why You Cant Add Warm Breast Milk to Cold
Parenting Toddler Safety

Why You Cant Add Warm Breast Milk to Cold

Bottles and jars of food easily lose heat when they are opened, so you want to store them in the refrigerator or freezer.

The same is true of breast milk. Its nutrients will curdle if exposed to extreme temperatures. 

If you are nursing, you may need to express different times of the day.

Most nursing moms wonder if they can mix breast milk with refrigerated or cold milk. However, this is not recommendable. 

But are there reason why you cant add warm breast milk to cold? Well, read on to know more. 

Reasons Why You Cant Add Warm Breast Milk to Cold Milk?

Like a cold drink won’t be able to warm you up on a hot day, cold milk won’t combine with warm milk.

But that’s not because of what your mother told you—it’s actually because of science.

By adding warm milk to cold milk, the temperature of the cold one increases almost immediately, creating great conditions for bacteria growth.

Usually, breast milk has a temperature of around 98.6 degrees F while one from the refrigerator can have a temperature of around 38 to 40 degrees F.

By mixing the warm and cold milk, the cold milk temperature will most likely rise beyond 40 degrees. This promotes bacterial growth, which can make your baby sick.

Therefore, to protect your child from getting sick from bacteria, it is highly advisable to only use fresh, warmer breast milk for your little one.

To mix breast milk with pumped breast milk, peel off the shrink wrap from the fresh container of milk and refrigerate it.

While you are at this task, place the breast milk you pumped earlier into the refrigerator as well.

Nonetheless, you can also refrigerate breast milk that you have pumped the same day so that it attains the same temperature as the refrigerated milk.

After the milk has cooled, you can mix it with the refrigerated milk and give it to your child. 

Ways of Mixing Breast Milk at Different Temperatures

Generally, it is generally better for babies to drink warm milk than cold.

However, if your baby is hungry and you do not have the time to warm up the milk, you can give him or her some cold breast milk. To warm it up faster, try one of these methods:

1. Do Not Mix at All

When you’re feeding a baby with medical needs, always make sure to seal your expressed milk and store it in the refrigerator or freezer.

Never combine previously refrigerated milk with recently pumped milk. If you want to mix your expressed milk, use freshly pumped milk.

2. Warm Milk to Room Temperature Milk

While expressing milk at a sitting, a woman may release two batches of milk.

While the first batch is being expressed, the second batch may have already started to drain from her breasts. 

Scant research has been done on whether or not it is safe for a mother to add one batch of milk to another.

For this reason, there is a need for additional research before any conclusions can be drawn.

3. Warm Milk to Defrosted Milk

It is highly advisable to express milk into a clean container if you are still using a breast pump and store it in your fridge.

If you are using the pump to remove milk from a sterile container, you can then defrost that milk and feed your baby. Leftovers from the latter can be discarded.

4. Warm Milk to Frozen Milk

Mixing frozen milk with warm milk follows a process called layering, which minimizes the amount of time your baby must wait for his feed.

To layer breast milk, start by lowering the temperature of the warm milk. 

Once it is cool enough, place it in the refrigerator. Also, bring the frozen milk into the refrigerator.

Once both batches are cool, pour the warm milk into the frozen one.

5. Warm Milk to Refrigerated Milk

Before mixing refrigerated and room-temperature breast milk, let the refrigerated milk cool at room temperature for about 15 minutes.

You can speed up the process by putting a bottle of warm (not hot) breast milk in a bowl of cold water.

Then, when it’s cool enough, add the warm breast milk to the combined portions.


Here’s the scoop on why it is not recommended to add warm breast milk to breast milk that is cold: because they’re both at different temperatures, and you need to either warm or cool one batch to make them the same temperature.

If you cool the warm milk to make it the same temperature as the cold milk, your breast milk loses some of its antibodies (an anti-infective ingredient). 

If you warm the cold milk to make it the same temperature as the warm milk, then you’ve over warmed all of your milk.

Remember: once you mix them, every bottle’s contents are that day’s oldest batch.

Frequently Asked Questions

What happens if you add warm breast milk to cold?

After a mother has pumped and frozen her breast milk, she may also be faced with a decision about how to rewarm the frozen milk so that it can be fed to her baby.

The two groups that study this kind of thing—the CDC and the Academy of Breastfeeding Medicine—say that combining milk does not pose any risks whatsoever.

Can you add warm breast milk to the refrigerated milk?

When feeding a child breast milk from a pump, try adding the expressed breast milk to frozen or chilled milk.

However, ensure that you cool the fresh breast milk, then thaw and shake the container of chilled or frozen milk before you add it to the fresh breast milk.

Is mixing warm breast milk with fresh breast milk okay?

If you want to combine the contents of two containers of breast milk, the milk should be cooled to room temperature before combining it.

If you want to add the recently pumped fresh milk to refrigerated milk from the same pumping, cool the freshly pumped milk in an ice pack bottle. 

Do this for about 20-30 minutes before adding it to previously refrigerated milk (from the same day). This will ensure that the temperature is not warmer than body temperature.


Iesha Mulla

Iesha is a loving mother of 2 beautiful children. She's an active parent who enjoys indoor and outdoor adventures with her family. Her mission is to share practical and realistic parenting advice to help the parenting community becoming stronger.

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