To thaw frozen milk, hold the bag or bottle under warm water until it’s at a comfortable temperature or let it defrost in the refrigerator overnight. Don’t use the microwave for defrosting or warming, because it kills the nutrients in breast milk and hot spots can develop.

Once you’ve thawed frozen milk, you can keep it in the refrigerator for up to 24 hours. If it’s at room temperature, use it within 1 hour. (If you haven’t used it in that time, you’ll have to throw it away, since you can’t refreeze it.) If you need to transport milk, keep it cold until just before using.