Your Guide to Warming Up Breast Milk

You can heat your baby's milk but it needs to be done the right way. Learn how to warm up breast milk safely and effectively.

Medically reviewed by Rebecca Agi, MS, IBCLC

How you feed your baby is a personal choice. You may opt to use formula, nurse, or pump—all of which are totally OK. But if you do the latter, you'll need to learn all about storing breast milk properly and how to serve it to your little one.

First things first, pumped milk can stay in the fridge for up to four days and in the freezer for up to six months (although up to a year can be fine too), according to the Centers for Disease Control and Prevention (CDC).

Before serving thawed breast milk to your baby, you may decide to warm it up. You should opt for somewhere between room temperature and body temperature. But make sure it's not too hot—around 99 degrees Fahrenheit is a good guideline. Here's what else you need to know about warming up human milk safely and effectively.

Do You Have To Warm Up Breast Milk?

There's no harm in giving your baby cold milk. "It is not necessary to warm your breastmilk and can be served cold or room temperature. Although, some babies may have a preference," says Wendi Andria, MSN, RNC-OB, IBCLC, a lactation specialist from South Shore University Hospital in Bay Shore, New York.

Since human milk is warm when babies nurse, they may prefer the familiarity of the temperature. Warming the milk also helps mix everything together (fat tends to separate when milk is cooled down in the fridge or freezer). Research shows warming the milk may also be beneficial to premature babies.

Be careful not to go overboard, though: Too much heat can destroy the milk's enzymes and immunizing properties. Plus, warming milk above 104 °F might scald your baby.

How To Warm Up Breast Milk From the Refrigerator

There are simple and effective methods for warming human milk. “If you choose to warm your breastmilk, it's best done over a period of 20 minutes using lukewarm water,” says Andria. “You can place your bottle or storage container in a bowl of warm water or hold it under warm running water." Make sure you follow the instructions properly so you don't scald your little one.

Use warm water

Get a bowl of warm water; you can gently heat the water on the stove or source it directly from the faucet. Place a tightly-sealed bag or bottle of human milk into the water. Let the milk sit until it reaches body temperature. If the water cools too much, replace it with more warm water until the milk is warmed properly. Swirl the milk (do not shake) to incorporate the separated fat.

Run under the tap

As another method, you can run tightly-sealed human milk directly under the faucet. Make sure the tap water is warm (not hot) and swirl the bottle before feeding it to your baby. This method works well, but it wastes plenty of water. Therefore the first method is preferred when warming human milk.

Test the temperature

Never feed your baby without checking the temperature of the milk. To do this, shake a few drops onto your wrist. The liquid should feel neutral—not too hot or cold.

Sometimes thawed breast milk doesn't smell very good, and it can also have a soapy, metallic taste. If this happens, it doesn't mean the milk is bad. The strange sour smell and taste are from an enzyme in the milk called lipase. Lipase naturally breaks down the fats in the milk during storage. It is still safe to give the milk to your baby, but keep in mind that your child may not drink it if they don't like the way it tastes.

Related: Breast Pump Pointers: Your Ultimate Pumping Guide

How To Warm Thawed Breast Milk From the Freezer

It's easiest to defrost frozen human milk in the refrigerator before warming it. That can take up to 12 hours. Use defrosted milk within 24 hours, advises Kelly A. Hightower, RN, a certified lactation counselor.

You can also heat frozen human milk with the warm water method outlined above; however, it will take significantly more time.

Do You Need a Bottle Warmer?

A bottle warmer is probably the easiest way to heat up a bottle of human milk, especially for middle-of-the-night feedings when you don't want to wait long. You can buy a bottle warmer online or at a local store, but be sure to follow the directions closely to avoid overheating.

How Long Is hawed Breast Milk Good for After Warming It Up?

Warmed milk from the fridge should be used within two hours. If it's not used, it should be thrown away.

"Once your milk is warmed, the ability of the milk to inhibit bacterial growth is decreased, so it is not recommended to place your milk back in the refrigerator," explains Andria. "The baby’s mouth touching the milk leads to bacterial growth in the milk. If your baby does not finish the feeding it is safest to use that leftover milk within one to two hours."

Also, thawed milk should never be refrozen. Thawed milk can stay at room temperature for up to two hours and in the fridge for up to 24 hours.

Related: Bottle Sterilizers Aren't a Must-Have, But These 10 Get Our Baby Bottles So Satisfyingly Clean

Can You Microwave Breast Milk?

Skip the microwave. This appliance will distribute heat unevenly, increase the chances of burns, and also deplete the nutrients in the breast milk.

What's more, a policy statement from the American Academy of Pediatrics (AAP) published in the August 2018 edition of Pediatric says this practice isn't best. "Since heat can cause plastics to leak BPA and phthalates into food, avoid microwaving food or beverages (including infant formula and pumped human milk) in plastic when possible," says an accompanying report, adding that these chemicals have been linked to health problems.

Related: How Long Can Breast Milk Stay Out?

Should You Use a Stovetop To Heat Breast Milk?

No, you should never use the stovetop. Never place your bottle in boiling water on the stovetop. You can easily overheat the breast milk this way, and it's not safe with plastic bottles, which can melt in the extreme heat. Again, heating plastic bottles at high temperatures can also be harmful to your health.

The Bottom Line

You don't have to warm human milk before giving it to your baby. But if you decide to do that, you can do so using a bottle warmer, a bowl of warm water, or under the tap. Either way, you want to avoid overheating the milk. And make sure to throw it out no more than two hours after it's been warmed.

Additional reporting by Donna Murray, RN, BSN.

Related: Is It Possible to Get Pregnant While Breastfeeding?

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