Should I Throw Away Unused Thawed Breast Milk?

Hi Emily! I read your breast milk storage article and watched your Instagram stories on breast milk, but neither of those answered my question. Per the CDC, you should not use breast milk that’s been thawed more than 24 hours. Currently all my breast milk is stored in 4-ounce bags, but my daughter is starting to eat more than that, so I’d like to send her to day care with an extra bag. But if it isn’t all used, do I really need to throw it away or can I send it back to day care the following day? Why is freshly pumped milk safe in the fridge for four days but thawed milk is not?

—Wasting Milk Is the Worst

Obviously you do not need to get me started on the fact that we don’t have enough detailed information about breast milk storage. What I argue in the post you reference is that the existing guidelines about storage, including leaving it out and in the fridge, are probably way too conservative. The limited data we do have shows very little bacterial growth after four days in the fridge or much longer periods in the freezer. What we are missing is how much longer this could go — if there is no bacteria after four days, we’d ideally want to know when there is significant growth. Anyway. I have said this before.

Your question is a bit more nuanced but, I think, is answerable. Imagine you have a “budget” of time. Being conservative, we could say this is four days in the fridge plus six months in the freezer. You can imagine combining this budget. If you initially froze the milk after a day, then you have three fridge days left after defrosting. If the milk was sitting in the fridge for four days before freezing, though, you’d want to use it right away.

If you thought we should have more relaxed guidelines about fridge storage (which, generally, I believe we should), then you would factor in more possible fridge time.

My sense is the CDC guidelines are written to be conservative and cover the situation in which you’ve already left the milk in the fridge for a longer period. If that’s not the case, sending the milk multiple days in a row should be fine.