How to Store Breast Milk

A Comprehensive Guide to That Liquid Gold

There’s a reason parents call breast milk “liquid gold” for babies: it’s chock-full of nutrients, immune-boosting antibodies, good-for-the-gut bacteria, and enzymes that aid in digestion. For new Moms, safe storage guidelines for breast milk can be confusing—but knowing how to store breast milk properly is important. We’ve rounded up everything you need to know to ensure not a single drop of that liquid gold goes to waste.

Beyond the basic guidelines, understanding why certain storage methods are recommended can provide greater confidence in your choices. Breast milk is a dynamic living substance, and its composition can subtly change over time, even during storage. Proper handling minimizes the degradation of its beneficial components and reduces the risk of bacterial contamination.

How Long Should You Breastfeed?

The American Academy of Pediatrics (AAP) has historically recommended exclusive breastfeeding for the first six months of your baby’s life. In 2022, the AAP updated its breastfeeding recommendations to include extended breastfeeding beyond the first year:

“Updated AAP guidance continues to recommend exclusive breastfeeding for six months, with complementary foods introduced around six months. Under the new policy, the AAP now supports continued breastfeeding until two years or beyond, as mutually desired by mother and child.”

The World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF) also recommend extended breastfeeding up to age two and beyond as the optimal feeding practice. Research has consistently demonstrated that extended breastfeeding benefits your toddler’s general health, nutrition, and cognitive and social development.

Extended breastfeeding offers ongoing immunological support, adapting to the child's needs as they grow. It can also provide comfort and security during times of illness or stress. Remember that the duration of breastfeeding is a personal decision, and these recommendations serve as a guide based on scientific evidence.

Will You Need a Breast Pump?

Not every new mom will need a breast pump, but most use one eventually, if only to take a (well-deserved) break from breastfeeding. You may need a breast pump if:

• Your baby is having trouble nursing—or isn’t nursing at all—and you need to maintain your milk supply. Pumping regularly signals your body to continue producing milk, which is crucial if your baby is unable to nurse directly due to prematurity, latch difficulties, or illness.
• You plan to return to work part- or full-time and would like to continue feeding your baby breast milk. Pumping allows you to provide your baby with the benefits of breast milk even when you are physically apart.
• You’d like your baby to be fed breast milk exclusively but would want other caregivers to be able to participate in feedings. Expressed milk allows partners, grandparents, or other caregivers to bond with and feed the baby, offering you flexibility and support.
• You’d like to be able to go out without your baby for more than a few hours at a time. Having a stash of stored breast milk provides freedom and peace of mind when you need some time away.
• You are experiencing (sometimes painful) engorgement and need relief without necessarily wanting to feed the baby immediately.
• You want to increase your milk supply.
• Your baby has a cleft palate or other condition that makes direct breastfeeding challenging.

If you are staying home with your baby, are breastfeeding on demand, and your baby is gaining the appropriate amount of weight, you may not need an electric breast pump. A manual breast pump may be adequate for managing engorgement or increasing your supply. Manual pumps can be particularly useful for occasional pumping or travel due to their portability and lack of need for a power source.

Breast Milk Storage Guidelines

The Centers for Disease Control (CDC) has created guidelines for the safe storage of breast milk, but also note—significantly—that various factors, like milk volume, the room temperature where you’re pumping, temperature fluctuations in your fridge or freezer, and cleanliness of the pumping environment can affect how long you can safely store breast milk. Maintaining a clean pumping environment, washing your hands thoroughly before pumping, and using properly sterilized equipment are fundamental to safe milk storage.

These guidelines are intended for mothers of full-term infants with no health complications. Use more conservative guidelines if your baby is preterm, in the NICU, or is otherwise ill. Preterm and immunocompromised babies are at higher risk of infection, so stricter storage protocols are necessary. Consult with your pediatrician or a lactation consultant for specific guidance in these situations. 

If your pregnant or postpartum brain is reeling, the AAP has a handy tip for remembering safe storage rules. Just follow their “rule of fours”: Breast milk can be safely stored at room temperature for four hours and in the fridge for four days. While the "rule of fours" is a helpful mnemonic, it's crucial to understand the nuances and exceptions to these guidelines, which we will explore further.

How Can You Store Breast Milk?

You have a few options for safe breast milk storage. They recommend storing breast milk in breast milk storage bags or clean food-grade containers with tight-fitting lids. Avoid any plastic marked with the recycle symbols #3 or #7, indicating that the plastic contains BPA. BPA (Bisphenol A) is a chemical that was previously used in some plastics and has raised health concerns. Look for containers specifically labeled "BPA-free." (Polypropylene plastic, marked with the recycle symbol #5, is a safer alternative.) Glass containers are also an excellent option for breast milk storage as they are inert and easy to clean, although they can be less convenient for freezing due to the risk of breakage.

There are three kinds of containers for safe breast milk storage, including breast milk storage bags, bottles, and breast milk storage trays (for freezing):

• Reusable silicone breast milk storage bags are an eco-friendly alternative to plastic storage bags. But they are more expensive and will need to be cleaned and thoroughly dried between uses to prevent bacterial growth. Ensure the silicone bags are food-grade and designed for freezing if you intend to freeze milk in them.
• Pre-sterilized plastic breast milk storage bags are inexpensive, compact, and disposable. They also can be frozen in a flat package, clearing up freezer space and allowing for quicker thawing. But they’re also a less eco-friendly option. When filling plastic storage bags, avoid overfilling and lay them flat to freeze to maximize freezer space and reduce the risk of leakage.
• If you’re using a pump, most come with glass or plastic bottles that you can pump into directly. While eco-friendly and convenient, it can get expensive if you’re pumping frequently and need a large storage capacity. Having a dedicated set of bottles for pumping and feeding can streamline the process.
• Breast milk storage trays are basically ice cube trays for your breast milk, and each portion typically holds around one ounce of milk. They’re a convenient option, allowing you to thaw the exact amount of milk you need, reducing waste, but not the best option for storing a large amount of breast milk long-term due to the increased surface area exposed to air, which can impact quality over extended periods. Once frozen in the trays, transfer the milk cubes to a labeled freezer-safe bag or container for longer-term storage.
• Clean, food-grade containers with tight-fitting lids, such as small glass jars or BPA-free plastic containers, can also be used. Ensure they are thoroughly washed and dried before each use. Choose containers of appropriate sizes to minimize air exposure.

Use waterproof labels to label each container with the date you expressed the milk (the “first in, first out” rule applies here—you’ll want to use the oldest stored milk first). Include the time of expression as well, especially if you are storing milk at room temperature.  If your baby is in daycare, also include your baby’s full name on the label.

General Breast Milk Storage Tips

• Breast milk should be refrigerated or frozen as soon as it’s expressed, preferably within one hour. The sooner you cool or freeze the milk, the better it retains its quality and reduces the risk of bacterial growth. If immediate refrigeration or freezing isn't possible, store it in a clean, sealed container at room temperature for the recommended time limit based on the temperature.
• Storing milk in smaller 2-4 ounce amounts may help reduce waste, especially for newborns who don’t consume more than four ounces at each feeding. Thawed breast milk must be used within 24 hours and cannot be refrozen, so thawing only what you anticipate needing minimizes potential waste.
• Refrigerated milk has less fat loss and more antibacterial protective properties than frozen milk. Prioritize using refrigerated milk within the recommended timeframe whenever possible. Freezing can slightly alter the fat globules and destroy some of the beneficial enzymes and antibodies, although it still provides significant nutritional value.
• Always label your breast milk storage containers clearly and legibly with the date and time you expressed the milk. Consistent and accurate labeling is crucial for safe and efficient use of your stored milk.
• Always use the oldest breast milk first to ensure optimal quality and nutrient content. This "first in, first out" (FIFO) method helps prevent waste. Organize your freezer and refrigerator so that older milk is easily accessible.
• Squeeze any excess air out of breast milk storage bags carefully before sealing them to minimize oxidation and freezer burn. Lay bags flat to freeze for more efficient storage. Ensure the zipper or seal is completely closed to prevent leaks.
• If your baby will attend daycare or other childcare outside your home, include your baby’s full name (along with the date) on the label. This ensures that your baby receives the correct milk at the childcare facility.
• The CDC advises against mixing warm breast milk with milk that has been previously cooled or frozen. Cool freshly expressed milk completely in the refrigerator before combining it with previously stored milk to avoid warming the older milk and potentially encouraging bacterial growth. You can store the freshly expressed milk in a separate container in the refrigerator until it has cooled, then combine it with the older milk in a single storage container.
• Consider keeping a log of your pumping sessions and the amount of milk expressed. This can help you track your supply and plan your storage needs.
• Avoid storing breast milk in areas of the refrigerator or freezer that experience frequent temperature fluctuations, such as the door.

How to Store Breast Milk in the Refrigerator

CDC guidelines state that freshly expressed breast milk can be stored in the refrigerator for up to four days (though it’s optimal to either use or freeze refrigerated expressed milk within three days). Thawed breast milk should be used within twenty-four hours (start the countdown once the milk is thawed, not when you first take it out of the freezer).  If the thawed milk smells sour or off, discard it.

Milk should be stored in the back of the refrigerator, where it’s the coolest. Never store breast milk in your refrigerator door—the door being opened and shut all day may make the milk too warm. Use a designated area in the back of the fridge for your breast milk to further ensure stable temperature.

Once you’ve thawed breast milk, it should be used within twenty-four hours and should never be refrozen. Make sure your caregiver also understands this.

How to Store Breast Milk in the Freezer

Per the CDC, breast milk can be frozen for up to twelve months, but using frozen milk within six is ideal (the longer your milk is frozen, the more its nutritional qualities diminish). Again, milk should be stored in the back of the freezer, where it’s coolest, and never in the freezer door. A deep freezer maintains a more stable temperature than a refrigerator freezer.

Because breast milk expands when it’s frozen, never fill a storage bag beyond the maximum fill level (generally six ounces). Leave an inch of space at the top if you’re using a different container for storage. Lay storage bags flat in the freezer to freeze quickly and save space. Once frozen solid, you can organize them vertically like books. 

How to Store Breast Milk at Work

Pumping success at work relies on the right equipment, so make sure you pack a breast pump bag properly. Invest in a high-quality insulated cooler bag and reliable ice packs to ensure your milk stays cold during your commute and workday.

Freshly expressed milk can be stored in an insulated cooler with ice packs for up to twenty-four hours. At-work storage options include:

• If you have access to a refrigerator, store your milk as you would at home in labeled storage bags, bottles, or other clean, food-grade containers (it may be helpful to use a small lunch bag or dedicated container to keep your milk together in one space and prevent anything from being accidentally knocked over or mistaken for someone else's food).
• If a refrigerator is not readily available, store your milk in a reliable insulated cooler bag with sufficient ice or freezable gel packs. Consider using a digital thermometer inside the cooler to monitor the temperature and ensure it stays below 40°F (4°C). We love the PackIt for this job—it’s lined on all sides with built-in freezable gel, so you don’t have to worry about adding separate ice cubes or additional ice packs, making it a convenient and efficient option for on-the-go storage. Ensure the PackIt is fully frozen before use.
• Discuss storage options with your employer beforehand to identify the most convenient and safe place to store your milk during the workday.

How to Thaw Breast Milk

Remember, you always want to use your oldest breast milk first to preserve as many nutrients as possible (that’s why labeling is so important). You can safely thaw your breast milk by:

• Leaving it in the refrigerator overnight (remember, once completely thawed, you’ll want to use it within twenty-four hours). This is the safest and most recommended method for thawing breast milk as it helps maintain milk quality and minimizes bacterial growth. Plan ahead and move frozen milk to the refrigerator the night before you intend to use it.
• Placing the sealed storage bag or container in a clean container of lukewarm water. Gently swirl the milk to help it thaw evenly. Avoid using hot water as it can damage the milk's nutrients.
• Holding the sealed storage bag or container under lukewarm (not hot) running water. Gently agitate the milk while thawing. This is a quicker method but requires more attention.

Once breast milk is warmed or comes to room temperature, you’ll want to use it within two hours. Additionally, never thaw or heat breast milk in the microwave. Not only will the heat destroy nutrients, it can also create hot spots that can burn your little one’s mouth.

How to Feed Your Baby Expressed Breast Milk

Some good news: Warming and feeding your baby breast milk is (thankfully) uncomplicated. In fact, breast milk doesn’t need to be warmed at all—you can feed your baby cold milk if they don’t mind! Offering cold milk can be particularly convenient when you are on the go. If you do want to reheat your breast milk, the CDC has a few tips:

• Keep the milk in its sealed storage container or bag, and place it in a bowl of warm water or run it gently under a lukewarm tap. Avoid submerging the entire bag, especially near the opening, to prevent contamination.
• Check the temperature of the milk carefully before feeding your baby (just dab a few drops on the inside of your wrist; it should feel lukewarm, not hot).
• Do not heat breast milk directly in the microwave or directly on the stove as these methods can cause uneven heating and nutrient damage.
• You can use a bottle warmer with a breast milk setting, which provides a gentle and consistent warming method. Follow the manufacturer's instructions for your specific bottle warmer.
• If your baby doesn’t finish their bottle of warmed or room temperature breast milk, you can use the remaining portion for another feeding within two hours. After that two-hour window, any leftover milk should be discarded to minimize the risk of bacterial growth. It's saliva that introduces bacteria, so once the baby has drunk from the bottle, the clock starts ticking.

Breast Milk Storage FAQs

Why Is Your Milk Separating?

It is completely normal for breast milk to naturally separate into layers while being stored, especially after refrigeration or freezing. You’ll typically see a milky bottom layer and a creamier, fattier layer on top. Just gently shake, mix, or swirl the container gently to combine the layers before you feed your baby. Avoid vigorous shaking, which can damage some of the milk's components.

What If Your Power Goes Out?

Panicking is understandable if you have a freezer full of breast milk and wake up to a blinking clock and zero power. But take a few calming breaths because your milk will remain safe for your baby, probably for longer than you’re imagining.

According to CDC guidelines, breast milk stored in a full, unopened freezer is kept safe for up to forty-eight hours (and about twenty-four hours if half full). Why? A full freezer has more frozen items, keeping items colder for longer.

If left unopened, your fridge will keep breast milk safe for four hours. What’s the main message here? Try to avoid opening your freezer or fridge during a power outage. Once power is restored, check your breast milk. It can be refrozen if it’s thawing but still contains ice crystals. If it’s completely thawed but still cool, you can move it to the fridge—just make sure to use it within the next twenty-four hours (and throw it away if you don’t).

Can You Fly with Breast Milk?

Your breast milk can be safely stored in an insulated cooler for up to twenty-four hours, is considered “medically necessary” by the Transportation Security Administration (TSA), and does not need to fit within a quart-sized bag.

Let your TSA agent know you’re traveling with breast milk, and they can screen your cooler separately from your carry-on. Storing your breast milk in clear storage bags will help speed up the process. 

Why Does Your Milk Smell or Taste Soapy?

Your thawed milk can look, smell, and taste differently than freshly expressed milk, and if you detect a soapy smell or taste, high lipase activity is the likely culprit. Lipases are enzymes found in all breast milk, and they do not indicate the milk is unsafe for your baby to drink.

And while it may be perfectly fine to drink, your baby may have their own opinions. If your baby rejects the milk, the La Leche League recommends mixing the thawed milk with cooled, freshly expressed milk.

Is It Safe to Store Milk in a Shared Refrigerator?

Yes! We recommend keeping your expressed milk in a cooler to prevent spills and ensure proper cooling on the way home. Again, ensure you’re storing your milk in the back of the refrigerator.

Is Your Milk Safe for Your Baby if You Have Thrush?

Thrush is an overgrowth of yeast that can cause an infection in your nipple or breast while nursing. If you’re worried that means you won’t be able to feed your baby while you have thrush, don’t be. It’s safe to continue nursing and feeding expressed milk while you are being treated for thrush. Similarly, using milk that was frozen while you had thrush is safe to feed your baby while you’re still being treated.

However, because freezing milk doesn’t kill the yeast, it’s possible your healthy baby could be reinfected. Avoid using breast milk that was expressed and frozen while you had thrush once you’ve completed treatment.

Finding What’s Right for You

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