Whether you’re going back to work or are on the go, you may want to freeze your breast milk for feeding flexibility. Depending on what type of freezer you use, frozen breast milk may stay good for three months to a year.

Studies have shown that freezing milk doesn’t damage important macronutrients and other benefits, like antibodies, for at least nine months or longer. To feed previously frozen milk to your baby, simply thaw the milk and serve cool or warm to body temperature.

Read on to learn different methods you can use to thaw breast milk, plus other tips for breast milk safety.

You can thaw frozen breast milk by placing it in the refrigerator overnight or for approximately 12 hours. From there, you can store thawed breast milk in your refrigerator for up to 24 hours. After that, the milk might be more apt to grow bacteria.

Any milk used to feed your baby throughout the day should be discarded after the feeding or within one or two hours. Learn more about how long breast milk can safely sit out.

To warm milk that’s been thawed in the refrigerator, place it under warm running water until it reaches body temperature. Be sure to test the milk before offering it to your baby to ensure it won’t burn their mouth. You can also swirl the milk to mix in the cream of the milk that rises during freezing.

You may thaw frozen breast milk directly from the freezer by placing it under warm running water, in a warm water bath, or in a bottle warmer. Doing so can only take a few minutes, but remember to keep the water warm and not hot or boiling to avoid burning your baby.

Once milk has been thawed using this method, it should be used within two hours.

Thawing breast milk at room temperature is not recommended. There are guidelines, however, for how to treat thawed milk once it’s at room temperature:

  • Use thawed breast milk within two hours after it’s been left at room temperature.
  • Discard thawed milk within one or two hours after your baby started feeding to avoid bacterial contamination.
  • Don’t refreeze breast milk that’s already been thawed. There’s little information on this process and how it may change the milk’s bacteria and nutrition.

Thawing breast milk using a microwave isn’t recommended. Doing so may destroy the beneficial nutrients in the milk.

The temperature of the milk can also be inconsistent throughout when you microwave it. This can lead to hot spots to develop in the milk that may burn your baby’s mouth. Instead, thaw in the refrigerator overnight or use warm water.

The differences between how long you can keep frozen breast milk has to do with the temperature inside your freezer compartment.

  • Breast milk stored in a standard refrigerator’s freezer (with its own door) can stay good for up to nine months. Ideally, you should use this milk within three to six months.
  • Milk stored in a dedicated deep freezer or chest freezer can stay frozen for up to one year. Ideally, you should use the milk between six months and a year.

While your milk is safe within these guidelines, studies show that milk quality changes slightly over time. Fat, protein, and calories may decline in milk that’s frozen over 90 days. After three months, the acidity of the milk may increase.

A few smaller studies have shown that vitamin C may decrease after five months of frozen storage.

That said, colostrum stays stable for at least six months when stored in a deep freezer. Other studies share that milk frozen nine months or longer still contains the important macronutrients and immunoactive proteins.

Why does my milk look or smell funny?

You may notice that the color of your breast milk varies from pumping session to pumping session. This has to do with your diet and the time frame in your baby’s life when the milk was expressed. The composition of your breast milk changes over time as your baby gets older.

Thawed breast milk may also smell different than fresh because of a breakdown in fatty acids. This doesn’t mean it’s unsafe to drink or that your baby will reject it.

Freezing breast milk isn’t complicated, but following a few guidelines will ensure your milk is safe:

  1. Wash your hands and all storage bags or containers.
  2. Label the bags or containers with the date and, if necessary for your child care provider, your child’s name.
  3. Express milk. Storing it in 1- to 4-ounce amounts may be best to limit the amount of waste. Store in smaller amounts for younger babies. As your baby gets older and begins to eat more, you can store in larger amounts.
  4. Chill and store. If you can’t freeze your milk immediately, refrigerate and freeze within 24 hours. Remember to leave space at the top of your container to account for any expansion of the milk during freezing.
  5. Don’t combine. Don’t add fresh milk to already frozen milk. Fresh milk can rewarm the frozen milk, which may invite bacteria. If you must add ounces together, cool the fresh milk first. Otherwise, store in a new container.
  6. Use oldest milk first. It may be helpful to store your newly pumped milk in the back of your stash, from newest to oldest. When reaching for frozen milk to give your baby, start with the oldest milk first.

Stock up on breast milk storage bags or containers.

Traveling with frozen milk? Here are some tips that can help make your journey easier.

Know the rules

In the United States, you may travel with a reasonable amount of breast milk per Transportation Security Administration (TSA) rules. You’ll need to disclose your breast pump as a medical device and declare your milk while going through security.

If the milk is totally frozen, agents won’t need to test your milk. If it’s thawed or semisolid, agents may inspect each container of milk for explosives. Ask your agent to put on clean gloves to prevent contamination.

Ask ahead

Request a hotel room with a freezer during your stay. If that’s not an option, try making arrangements to keep your cooler of milk in the hotel’s freezer. While not as convenient, taking your milk to the front desk and asking to have it placed in your personal cooler will still get the job done.

Keep it cool

Consider using dry ice during your travels to keep your milk as cold as possible. If that’s not an option, refill your cooler with ice from different eateries in the airport or rest stop.

Learn more

International travel may involve additional rules and regulations. Read up on your rights before you go. For information on domestic travel in the United States, check out the TSA guidelines for traveling with breast milk.

The Centers for Disease Control and Prevention doesn’t recommend freezing formula. While freezing isn’t necessarily unsafe, it may cause the different components of the formula to separate.

Freezing expressed breast milk is a great way to stock up if you’re returning to work or would like feeding flexibility for date nights or other outings. Feeding thawed milk is safe and provides your baby with the nutrients they need to grow and thrive.

Healthline and our partners may receive a portion of revenues if you make a purchase using a link above.