Whether you're exclusively breastfeeding or pumping milk to feed your little one (or any combination of the two), knowing how to safely store your breast milk is key to ensuring it stays fresh, nutritious, and safe.

This guide will walk you through what to do when you put your breast pump away. You'll learn the best ways to store, thaw, and warm your breast milk, so you can give your baby the healthiest start, whether you're at home or on the go.

Why is Proper Storage Important?

Properly storing your breast milk helps make sure your baby gets all the nutrients they need while also preventing the growth of harmful bacteria. Since breast milk is a living substance, it’s important to handle and store it correctly to keep it safe.

Preparing Your Breast Milk for Storage

Use the Right Containers

Breast milk should be stored in clean, airtight food-grade containers.

You can use:

  • Breast milk storage bags, which are made for freezing milk.

  • Hard plastic or glass containers with tight-fitting lids.

  • Baby bottles or breast milk storage containers, as long as they are sealed properly.

  • Make sure whatever container you use is BPA-free (safe for your baby) and has been thoroughly cleaned before use.

Is it Safe to Store Milk in Plastic Bags?

Yes, it is safe to store breast milk in plastic bags made specifically for this purpose. Just make sure the bags are BPA-free and made for freezer storage.

Label Your Milk

Each time you pump, label your milk with the date it was expressed. This will help you keep track of how long your milk has been stored and ensure you use it within the recommended storage times.

Combining Your Milk

If you’ve pumped milk at different pumping sessions, it’s best to cool your fresh, warm milk prior to mixing it with milk that has already cooled in the refrigerator. Once your fresh milk has cooled, you can safely combine milk from multiple pumping sessions and freeze for later use.

Freezing Your Milk

To save space and make storage easier, lay your breast milk storage bags flat to freeze. Just be sure to leave an inch of space, or "headspace", at the top of the bag, as the milk will expand as it freezes. This air gap in the top of the container can be removed once your milk is frozen. Not all glass bottles are freezer safe, so follow manufacturer's guidelines for safe freezing.

Breast Milk Storage Guidelines

This milk storage information is from the U.S. Centers for Disease Control and Protection (CDC) and the Academy of Breastfeeding Medicine ABM Clinical Protocol:

  • At Room Temperature: Freshly expressed breast milk can be stored at room temperature up to 77°F (25°C) for up to 4 hours. 
  • In the Refrigerator: Freshly expressed breast milk can be stored in the refrigerator at 40°F (4°C) for up to 4 days. It’s best to store your milk in the back of the refrigerator (where the temperature is most consistent), not on the door.
  • In the Freezer: If you want to store breast milk for a longer time, freezing it is a good option. Milk stored in a freezer can be stored for up to 12 months, but it’s better to use it within 6 months for the best quality. 

Is it Safe to Store Milk in a Cooler Bag or Ice Chest?

Yes, if you’re away from home, a cooler bag or ice chest with ice packs can be a safe option for up to 24 hours if your ice packs remain frozen. Replace them as needed, so that your milk stays cold (under 40°F or 4°C) until you can get it to the refrigerator or freezer.

What About Using a Breast Milk Chiller?

Portable breast milk chillers—like the Ceres Chill—can be a convenient option for storing freshly expressed milk while you're away from home, at work, or traveling. Unlike a cooler bag, many milk chillers are designed to keep breast milk at a safe temperature (under 40°F or 4°C) for an extended period without requiring loose ice.

Always follow the manufacturer's instructions for proper use, including how long the chiller will safely maintain the recommended storage temperature. Before adding freshly expressed milk, make sure the chiller has been properly pre-chilled if required by the manufacturer. Once you return home, transfer your milk to the refrigerator or freezer as soon as possible.

When You Are Ready to Use Your Stored Breast Milk

Thawing Frozen Milk

When you need to use frozen milk, begin by using the oldest milk first to keep your stored breast milk supply as fresh as possible. It’s best to thaw it in the back of the fridge overnight or under cool running water. 

  • Once thawed in the refrigerator, breast milk should be used within 24 hours. The 24 hour window starts when there are no longer ice crystals present in the milk.
  • Any breast milk that still has ice crystals present is still considered frozen and can be placed back in the freezer. 
  • Never microwave frozen milk, as it can destroy some of the nutrients and create hot spots that could burn your baby.

Warming Milk

If you need to warm milk that’s been refrigerated or thawed, you can:

  • Place the bottle or bag in a bowl of warm water for a few minutes. Lukewarm water trickling into the bowl can speed the process a bit.
  • Use a bottle warmer, but pause throughout the process to gently swirl to mix in the fatty part of the milk.
  • You can also offer your baby cold milk straight out of the fridge - some babies don’t mind! 
  • Make sure to always gently swirl after warming and test the milk temperature on your wrist before feeding your baby to ensure it’s not too hot.
  • If your baby doesn’t finish a bottle, any leftover milk should be used within 2 hours or discarded.

What NOT to Do with Breast Milk

Here are a few important things to remember about handling breast milk:

  • Do not refreeze milk once it has been thawed. Once thawed, it should be used within 24 hours and not refrozen.
  • Do not add freshly pumped warm milk to refrigerated milk, until you cool it in the refrigerator first.
  • Do not leave milk out for more than 4 hours at room temperature, or longer than 4 days in the refrigerator.
  • Never use a microwave to warm breast milk.

If this seems like a lot of detailed information, don't worry—you don't have to memorize it all. Save or print this simple infographic to keep on your refrigerator or share with your baby's caregiver. With a little preparation and the right support, you can safely store your breast milk and feel more confident pumping and feeding your baby, wherever your feeding journey takes you. 

Questions About Storing Your Breast Milk?

Every breastfeeding journey is unique. If you have questions about pumping, milk storage, returning to work, or feeding your baby, our lactation consultants are here to help. Schedule a virtual consultation for personalized guidance and support.

Disclaimer: Our classes and accompanying materials are intended for general education purposes and should not replace medical advice. For personalized recommendations, please consult your healthcare provider and/or lactation consultant.