Breast milk can be stored for between six hours and 12 months, depending on how it is stored. Store it for up to six hours at room temperature, five to eight days in the refrigerator, one day in an insulated cooler or up to 12 months in a freezer.
If breast milk is stored in the freezer, it needs time to thaw. Always thaw the oldest expressed breast milk first by putting it in the refrigerator the night before using it. It is safe to place the milk in a bowl of warm water or directly under a faucet with warm water for faster thawing. Swirl the bottle before using it, but do not stir or shake the milk. Breast milk should never be thawed at room temperature, as this causes the bacteria level of the milk to increase.