woman labeling bottles of breast milk for storage

Breast Milk Storage Guide: How to Keep Baby Safe

By Stacey Feintuch
Reviewed by Terri Major-Kincade, M.D.
March 19, 2024

Pumping or expressing breast milk allows you to have milk easily at your fingertips for your baby’s next feeding. But pumping in advance means you’ll need to store breast milk properly for it to stay safe and fresh.

Here are some tips and tricks for safe breast milk storage.

Choose the Right Gear for Safe Storage of Expressed Milk

When you’re looking to store breast milk, choose clean, sterilized food-grade glass or plastic containers. They should have tight-fitting lids or seals. You have a few different options:

Breast milk storage bags. Specially designed storage bags have a zip top and can be used in the refrigerator or freezer, says Melissa Kotlen, a registered nurse, private lactation consultant (IBCLC), and manager at Boram Postnatal Retreat in New York City. They take up less space in the freezer and are portable.

However, the bags can potentially rip. Help avoid damage by placing filled bags in plastic containers or by double bagging them. Never use disposable bottle liners or plastic bags not intended for storing breast milk.

Glass bottles. Glass bottles made for breast milk are safe and easy to clean but can break easily, Kotlen says.

Plastic bottles. Because of their greater durability, some people may choose plastic bottles. Look for hard-sided, BPA-free plastic that is opaque or clear. Avoid plastic bottles or containers with recycle symbol number 7—that means it may have been made with harmful chemicals.

Measure and Label the Milk Properly

labeled breast milk storage bags

To keep track of how fresh stored milk is, label each container with the date the milk was expressed. Use a smudge-proof marker. Some parents like to use color-coded labels to categorize the milk from oldest to youngest, in case the ink markings fade.

You should also label the amount of breast milk stored. To do this with the best accuracy, note the amount pumped in the bottle before storing it in the bag or container, and then indicate that amount. That’s because if you’re using breast milk bags, it’s easy to read an incorrect measurement after it’s poured into the bag because of how they fill up, Kotlen says.

When freezing milk, store it in units of 2 or 4 ounces, or the amount you give at a feeding. Smaller amounts are good for snacks or when your baby is younger and eats less. The smaller amount you store, the quicker it can be warmed, and the less risk you’ll need to dispose of leftovers.

Also, aim to fill the container three-quarters full at the maximum when freezing, Kotlen says. You’ll save yourself trouble by leaving that extra space. “When your breast milk freezes, the volume will expand,” says Jarret Patton, M.D., a pediatrician and author in Pennsylvania. “Leave that extra space at the top of your storage container so the package doesn’t burst or make a big mess.”

Keep Milk Stored at a Stable Temperature

To help prevent exposure to temperature changes, it’s best to keep your supply in the back of the fridge or freezer. “The back of the fridge or freezer tends to keep the most stable temperature to keep your breast milk fresh,” Patton says. And it’s coldest there, adds Kotlen.

Avoid storing milk in the door of the refrigerator or freezer. That way, you’ll protect milk from being affected by greater temperature changes when the door opens or closes.

Follow Breast Milk Storage Guidelines

breast milk storage guidelines chart

How long breast milk is good for depends on how you’re storing it—whether it’s at room temperature, in a fridge, or in a freezer.

Breast milk can be stored and stay safe and fresh for:

  • Up to 4 hours at room temperature on the countertop (77 F or cooler)
  • Up to 4 days in the refrigerator
  • About 4 months in a regular freezer
  • About 12 months in a deep freezer

Keep Track of Dates and Toss What’s Not Fresh

Be sure to periodically check the back of your fridge or freezer, too. “Always make sure you’re aware of what you have,” Kotlen says. “I’ve had too many moms find old bags of milk back there after the baby was weaned because it got covered by other frozen items.”

And to keep your supply fresh and help prevent waste, use the oldest milk first.

Thaw and Warm Breast Milk Safely

To thaw frozen breast milk safely, you have three options:

  • Place the container in a bowl of lukewarm water until thawed.
  • Set the container under running lukewarm water until thawed.
  • Put the frozen container in the refrigerator until thawed.

Then, use the milk within two hours of it fully thawing. Do not refreeze it.

You may choose to feed your baby cold, room-temperature, or warm milk. To warm refrigerated or thawed milk, place the container of milk in a bowl of warm water or under warm running water.

Do not put breast milk in the microwave or on the stove. Heating breast milk like this destroys nutrients and can make the milk too hot to be safe for your baby.

Safe Breast Milk Storage While Traveling

If you’re traveling, you can store breast milk with frozen ice packs in a cooler for up to 24 hours, Patton says. Then, use it right away, store it in the refrigerator, or freeze it.

If the milk was previously frozen and it stays frozen for the trip, you can put it in the freezer once you’re at your destination. Don’t refreeze it if it’s thawed, however. “If it has [thawed], then it needs to be put in the refrigerator and used in the next 24 hours,” says Kotlen.

If you’re traveling without the baby (such as for a business trip) and sending milk home, ship it on dry ice, Kotlen says.