A: To properly reheat breast milk, warm water on the stove (or use water from the sink faucet) and place the milk container in the warm (but not hot) water for a few minutes; never reheat breast milk in the microwave. According to the Academy of Breastfeeding Medicine (ABM), microwaving milk (including room temperature and frozen breast milk) can heat unevenly and create hot spots within the milk. A bottle warmer can give you more peace of mind for thawing and warming to a proper temperature if you’re unsure, though it’s not required.
Lastly, like regular milk, if breast milk spoils, you’ll know, and it’s always better to err on the side of caution when it comes to the safety of your milk supply. Remember that each time you reheat a bottle of breast milk, it will lose some of its immunologic properties, so whenever possible, try to make a fresh bottle (whether stored or straight from your breast pump) with only the amount your baby can eat.
For more information on reheating and breast milk storage, to connect with lactation experts in your area, and for additional resources, visit La Leche League or The Lactation Network.