How to Thaw Frozen Breast Milk (and Why Not to Refreeze It)

A freezer stash is a safety net, whether you’re heading back to work, planning a night out or just want backup. Thawing that milk the right way keeps it safe and avoids waste. The process is easy once you know the rules: thaw gently, use thawed milk within set times, and never put fully thawed milk back in the freezer.

This guide walks you through how to thaw frozen breast milk, how long it lasts afterward, and what to do in tricky situations like a power outage. It follows CDC guidance for healthy, full-term babies; if your baby is premature or in the hospital, check with the care team.

Before you thaw: oldest first

The CDC recommends thawing the oldest milk first. The CDC says frozen milk is best used within 6 months and acceptable up to 12 months (the AAP gives up to 9 months for a freezer with a separate door and up to 12 for a deep freezer, and the NHS gives up to 6 months), so rotating your stash helps you use milk while its quality is best. Check the date on the label before you pick a bag.

Also thaw only what you need. Milk frozen in small portions of about 2 to 4 ounces (60 to 120 ml) is easier to match to your baby’s appetite.

3 safe ways to thaw frozen breast milk

1. In the fridge overnight

Move the bag or bottle from the freezer to the fridge the night before you need it. This is the slowest method but the most hands-off. The CDC says milk thawed in the fridge should be used within 24 hours, counted from when the milk is completely thawed, not from when you took it out of the freezer. The ABM adds that slow thawing in the fridge causes less fat loss than thawing in warm water, and the NHS also suggests defrosting slowly in the fridge when you can.

Tip: put the bag in a clean bowl or container in case it leaks as it thaws.

2. In a bowl of lukewarm water

Place the sealed bag or bottle in a bowl of warm or lukewarm water. Warm or lukewarm is enough; the ABM suggests lukewarm water at most 104°F (40°C) for warming. Thin, flat-frozen portions should thaw faster than thick blocks, though the guidelines we read don’t test this.

3. Under lukewarm running water

Hold the sealed container under lukewarm running tap water until it thaws. This uses more water, so it works best for small portions when you need milk soon.

In each case, keep the container sealed so water can’t get in, then swirl gently to mix the fat back in.

What not to do

• Don’t use the microwave. The CDC says never to thaw or heat breast milk in a microwave, because microwaving can destroy nutrients and create hot spots that can burn a baby’s mouth. The ABM adds that microwaving significantly decreases the activity of immune factors in milk.
• Don’t use the stove or boiling water. The CDC says not to heat breast milk directly on the stove, and La Leche League says to avoid boiling. The ABM notes that overheating denatures milk’s protective proteins and lowers its fat content. Warm or lukewarm is enough.

How long does thawed breast milk last?

Where thawed milk is kept	How long it’s good for
Room temperature or warmed	Within 2 hours (the CDC’s printable chart says 1–2 hours)
Fridge	Up to 24 hours from when it is fully thawed
Freezer	Never refreeze milk that has fully thawed
Leftover after a feed	Use within 2 hours after your baby finishes feeding, then discard

These times come from the CDC’s storage guidance. For a quick use-by time, try our breast milk storage calculator, and see the full chart in our breast milk storage guide.

Other sources differ. The AAP’s HealthyChildren.org says thawed milk stored in the fridge is best used within 24 hours but may be used within 48 to 72 hours. The NHS says to use defrosted milk straight away. The ABM protocol doesn’t give a fridge time for thawed milk and notes that milk thawed for 24 hours shouldn’t be left out at room temperature for more than 2 hours. For leftovers, the CDC says 2 hours after the feed, the AAP says 2 hours (or, if quickly refrigerated, the next feeding), and the NHS says 1 hour. We follow the CDC’s 24-hour limit here because it’s the more cautious of the CDC and AAP times.

Can you refreeze thawed breast milk?

No, not once it has completely thawed. The CDC is clear: never refreeze breast milk after it has thawed, and the NHS says the same. The ABM protocol says there is too little information to make a recommendation, and La Leche League notes that research on refreezing is limited, but refreezing may break down nutrients and increase bacterial growth, so the accepted practice is not to refreeze thawed milk.

There is one exception worth knowing. According to the CDC, frozen milk that has started to thaw but still contains ice crystals can be refrozen. That might happen if a bag slips out of the freezer briefly, or during a short power outage.

If your power goes out

• Milk that still has ice crystals can go back into the freezer once power returns.
• Milk that has completely thawed but still feels cold should go in the fridge and be used within the next day, or thrown away.

Warming thawed milk

Thawed milk can be fed cold, at room temperature or warmed. If your baby prefers it warm, set the sealed container in warm water for a few minutes and test a few drops on your wrist before feeding. Our guide on how to warm breast milk covers bottle warmers and reheating questions.

Why thawed milk may look or smell different

Thawed milk often separates into layers. That’s just fat rising to the top; swirl it to mix. Some people notice a soapy, metallic or even rancid smell after freezing. La Leche League says the reasons are not well understood but it may be due to the breakdown of milk fats over time, and that if milk was stored properly it is safe and most babies will drink it. The ABM protocol likewise says there is no evidence that infants often reject milk because of this odor. See our guide to high lipase milk if your baby refuses it.

If your baby consistently refuses thawed milk, talk with a lactation consultant before building a large stash. They can help you figure out what’s going on and whether anything in your storage routine should change.

Planning your stash

A little planning makes thawing smoother:

• Label each bag with the date, and the amount if it helps.
• Freeze in feed-sized portions.
• Store milk at the back of the freezer, not in the door.
• If you’re pumping to build a stash, a realistic pumping schedule helps you avoid pumping much more than you can use.

When to call a doctor or lactation consultant

Call your baby’s doctor if your baby has vomiting, diarrhea, a fever, or seems unwell after a feed, especially if you’re unsure how the milk was stored or thawed.

A lactation consultant (IBCLC) can help if your baby won’t take thawed milk, if you’re storing milk for a premature or sick baby, or if you’re unsure how much to keep in the freezer. Find help on our breastfeeding support page.