Baby formulas come in two types: mixed or ready-to-feed. Refrigeration depends on a few factors, including whether you have used the formula or if it is a freshly mixed batch. Keeping the formula refrigerated for only the amount of time recommended, if recommended at all, keeps your baby safe from illness caused by bacterial contamination.
Leftover From a Feeding
The Nemours Foundation, which specializes in pediatric health, does not recommend refrigerating formula leftover after a feeding. Bacteria forms rapidly in a bottle left at room temperature, but it can still grow -- at a slower rate -- when the bottle is stored in the refrigerator. The University of Nebraska Extension explains that foodborne illness is transmitted by organisms you can't smell, see or even taste. These bacteria are troublesome for anyone, but especially dangerous for those with weaker immune systems such as babies. Throw away any leftover formula after feeding your baby.
Mixed or Ready-To-Feed
For future feedings, mix formula or use a ready-to-feed formula and pour it into bottles. This offers a convenient way to store the bottles before heating them so that they are readily available when your baby is ready to eat. Storing the premade bottles in the refrigerator prevents bacterial growth to prevent your baby from becoming sick. The University of Nebraska Extension recommends placing the bottles of formula in the coldest area of your refrigerator, ideally where it maintains temperatures below 40 degrees.
Keep prepared bottles at room temperature no longer than 2 hours, or 1 hour if the bottle is warmed. Dispose of mixed formula bottles within 24 hours after you prepare them and store them in the refrigerator. If using a ready-to-feed formula, store the bottles in the refrigerator for no longer than 48 hours. Some formulas have longer storage times; check the label for the storage recommendation.
To reduce the risk of bacterial contamination, sterilize bottles and nipple before you first use them. Thereafter wash the bottles and nipples in hot, soapy water. Boil water from your municipal water supply in case the supply becomes contaminated. Bottled water is safe to use without boiling if it specifies it is sterilized. Wash the top of the formula container under warm running water before opening it to clean away any dirt or other residue. Wash and dry your hands thoroughly before preparing the formula to clean away germs.