urrent recommendations, including those of the Academy of Breastfeeding Medicine (ABM Clinical Protocol #8, 2017 revision), consistently advise against using the microwave to thaw or heat breast milk, due to uneven heating, the difficulty of controlling temperature, and documented reductions in the activity of immunological factors above approximately 40 °C.

Leftover Milk in the Bottle After a Feeding: Can It Be Kept for More Than 2 Hours?