Theoretically, milk powder should not be given to children after 30 days of opening the package. Powdered milk that has been opened for just 40 days is not suitable to be fed to children again. To avoid waste, adults can continue to drink it. There are also some milk powder package instructions that indicate the shelf life of the milk powder after opening, if the time indicated is 60 days after opening, it is still drinkable at 40 days. In order to extend the shelf life of milk powder, ease the loss of nutrients and preserve the nutritional value as much as possible, milk powder should be stored in a relatively dry, cool and ventilated environment to avoid sunlight and moisture, and should be fed to the child in the shortest possible time.