Formula manufacturers recommend that prepared formula be discarded after 24 hours in the refrigerator. If you are using the powdered formula, a can of dry powder is good for one month once it is opened.
Freeze breastmilk if you do not plan to use it in the first 24 hours. Depending on your choice of freezer the milk can be stored for up to 3-6 months. Do not use the microwave when re-warming breast milk, but instead use warm water so the breast milk is heated evenly.
Formula or breast milk that is left over from a previous feeding should be discarded because bacteria from your baby’s mouth contaminates the nipple which in turn contaminates the milk.
When the milk is left out at room temperature, these bacteria multiply very quickly and you run the risk of making your child ill if fed this contaminated formula. Both formula and breast milk should only be left out of the refrigerator for one hour and then needs to be discarded.