It is always best to refrigerate or freeze breast milk right away, but sometimes situations arise that leave you with expressed breast milk sitting out. If this happens, many mothers worry that they have wasted a lot of hard work and could be at risk for their baby contracting an illness. But don't stress! The good news is that human milk has some very protective properties that allow it to stay safe and wholesome for longer than other foods.
According to CDC guidelines, freshly pumped milk can remain at room temperature (77 degrees Fahrenheit) for 6-8 hours, if it is in a clean, sealed container. However, if the room is warmer than that, it is best to keep it in the fridge within 4 hours.
While these guidelines are generally true for a breastfed infant, it's important to talk to your pediatrician about your specific situation and baby's needs as every child is unique. Also, these guidelines are for a mother who is not experiencing engorgement and has a healthy immune system.
Another thing to remember is that breastmilk can only be thawed and used once before it should be discarded. Reheating thawed breastmilk can cause it to re-freeze, which will break down the milk components and further degrade its antibacterial properties. If you are storing your thawed breastmilk in the refrigerator, be sure to move it to the back of the fridge where the temperatures are coldest, so that it stays chilled.