Here’s everything you need to know about safely storing, warming, and serving your breast milk to baby. 

Whether you’ve got a baby that will only drink their milk warm (if you know, you know…) or just need to thaw that milk that’s been on ice, there are a few things to keep in mind when it comes to reheating your liquid gold. We’re sharing all of that below, as well as recapping our guidelines for safe milk storage and thawing. 

Keep reading for tips on:

• Safely storing your freshly expressed milk
• Storing and using thawed breast milk
• Reheating breast milk and potential risks
• Safely handling warmed milk 
• And more! 

Remember that these guidelines are recommended for freshly expressed breast milk for healthy, full-term babies only. Always check with your pediatrician if you’re unsure about what’s best for your baby! 

Storing Breast Milk: Freshly Expressed Milk vs. Thawed Breast Milk

When storing your breast milk, there’s a lot to consider. Do you have access to a fridge? What’s the temperature? How long until you plan on feeding it to your baby? This is why it’s so important to have a plan and follow the guidelines set by the Centers for Disease Control (CDC) and the Academy of Breastfeeding Medicine (ABM).

In addition to paying close attention to the temperature and duration of time, it’s important to make sure that your storage conditions are clean, since this will minimize the risk of bacteria growth. That means clean hands and countertops, and no open food containers getting close to your milk in the fridge or freezer! 

Thawing Breast Milk: You’ve Got Options! 

When it’s time to thaw your frozen milk, you have a few options: 

1. Fridge: Thawing breast milk in the refrigerator can take between 4 and 12 hours, so it’s important to plan in advance! Place your milk storage bag in the fridge standing upright. Make sure that it’s not squished between any containers that could puncture or damage the bag. 
2. Warm running water:  You can also thaw your breast milk by covering it with a stream of warm running water. Just make sure that the temperature is no higher than 99 degrees! If it’s boiling, you could end up damaging the milk’s nutritional properties, or create “hot spots” that burn your baby’s mouth once the milk has been transferred to a bottle. 
3. Water bath: You can also place the bag in a bowl of warm water, swirling gently to speed defrosting and to make sure that the fatty parts of the milk (which may separate when frozen) are incorporated.

No matter what, you never want to thaw breast milk in the microwave or by using boiling water. 

Learn more about different ways to thaw breast milk here. 

Safety Considerations for Reheated Breast Milk

You’ve stored your milk, you’ve thawed your milk, and now you want to warm it up. You might be wondering: do I need to warm my milk before I feed it to my baby? 

The answer is no! Many babies are happy to drink milk straight from the refrigerator or at room temperature. Plus, sometimes reheating your milk simply isn’t an option — for example, you might be traveling and offering a bottle that’s been in an insulated cooler. 

Safe Methods for Reheating Breast Milk

1. Using a Bottle Warmer

A bottle warmer is one of the easiest and safest ways to reheat breast milk. Most models follow a similar process:

1. Fill your bottle with refrigerated or thawed breast milk.
2. Add warm (not boiling) water to the warmer’s reservoir.
3. Place the bottle in the warming chamber and ensure the cap is tightly sealed.
4. Choose your preferred temperature setting and warm until lukewarm.
5. Before feeding, test a drop on your wrist to confirm it’s not too hot.

Always follow the manufacturer’s cleaning instructions between uses and avoid leaving milk in the warmer longer than recommended. Overheating can damage nutrients and alter milk composition.

2. Using a Warm Water Bath

To gently reheat milk, submerge the sealed bottle or storage bag in a bowl of warm water until it reaches body temperature. You can also hold it under warm running water, though it may take longer. Ensure your container is tightly sealed to prevent leaks and never use boiling water, which can overheat the milk. As always, test the temperature on your wrist before feeding your baby.

3. Avoiding Microwaves

Never reheat breast milk in the microwave. Microwaves can cause uneven heating, creating dangerous hot spots that may burn your baby’s mouth and destroy important nutrients and antibodies. Instead, stick to gentle warming methods, such as a bottle warmer or a warm water bath, to preserve both safety and quality.

How Long is Reheated Breast Milk Good For & Signs It’s Gone Bad

Once breast milk is reheated, the clock starts ticking. Unlike freshly pumped milk, it must be used within 2 hours and cannot be refrigerated, refrozen, or reheated again. Warming milk more than once can encourage bacterial growth and reduce its nutritional quality.

Storage and Safety Guidelines

• Use within two hours of reheating, then discard any leftovers.
• Never return reheated milk to the fridge or freezer.
• Do not reheat milk more than once—fresh portions are always safer.

How to Spot Spoiled Breast Milk

Reheated or thawed milk can spoil, especially if stored too long or handled improperly. Check for these warning signs:

• Texture: Clumpy, stringy, or scummy consistency
• Smell: Fishy, rancid, or sour odor (a sign of oxidation)
• Mixing: Fat does not re-incorporate when swirled

 If you notice any of these, it’s time to discard the milk.

A slight color change—yellow, blue, or green—is perfectly normal, and gentle separation is expected. However, if the milk looks or smells off, trust your instincts and toss it.

Quick Tips for Reheating and Handling Breast Milk Safely

1. Label Every Bottle or Bag: Always label stored breast milk with the date, time, and number of ounces pumped. Use the oldest milk first to ensure freshness and safety. Organized labeling helps you track supply and prevents waste when reheating or feeding later.
2. Keep Portions Small: Because breast milk should only be reheated once, start with smaller portions and warm more if your baby is still hungry. This simple habit reduces waste and helps you make the most of every ounce of expressed milk.
3. Warm It the Safe Way: You don’t have to warm breast milk before feeding—room temperature or cold milk is perfectly safe. If your baby prefers it warm, consider a warm-water bath or a bottle warmer.
4. Follow Safe Thawing Guidelines: If your milk was frozen, thaw it gradually in the fridge or in a bowl of warm water before reheating. Never refreeze thawed milk, and always swirl (don’t shake) to mix separated fat evenly.
5. Practice Clean Handling: Wash your hands and keep all bottles, pump parts, and surfaces clean before touching stored milk. Limit how long milk sits out at room temperature to reduce bacterial growth.

For more tips about safe milk storage, check out the Pumping and Breastfeeding section on our blog, and explore milk storage options such as our Portable Breast Milk Cooler. 

Reheating Breast Milk FAQs  

• Can you reheat breast milk more than once?
  No. Reheating breast milk more than once can cause nutrient loss and increase the risk of bacteria growth. Warm only what your baby will drink in one feeding.
• How long can reheated breast milk sit out at room temperature?
  Reheated breast milk should be used within two hours and then discarded. After that, bacteria can grow and make the milk unsafe.
• What is the best way to reheat breast milk?
  Gently warm milk in a bottle warmer or a bowl of warm (not boiling) water until it reaches body temperature. Avoid microwaves or boiling water to preserve nutrients.
• Can you serve breast milk cold or at room temperature?
  Yes. Many babies are comfortable drinking milk cold or at room temperature, and it’s completely safe if the milk has been properly stored.
• How can you tell if reheated breast milk has gone bad?
  Spoiled milk may smell sour or rancid, look clumpy or stringy, or fail to mix when swirled. If it doesn’t smell or look right, it’s safest to discard it.