Whether you've decided to formula feed your baby from the start, are supplementing your breast milk with formula, or are switching from breast milk to formula, you're bound to have questions. Here are answers to some common queries about formula feeding. Do I need to sterilize my baby's bottles? Before the first use, you'll need to sterilize nipples and bottles in a rolling boil for 5 minutes. You can also sterilize them with a store-bought countertop or microwaveable sterilizer, but boiling works just as well and costs nothing. After that, it's not necessary to sterilize your baby's bottles and supplies each time you feed your baby. You will need to wash bottles and nipples in hot, soapy water (or run them through the dishwasher) after every use. They can transmit bacteria if not cleaned properly. How do I prepare my baby's bottles? Prepare your baby's formula by mixing water and the appropriate amount of powdered infant formula. The packaging on the side of the formula container will tell you how much to use. Carefully follow the directions. You can use tepid (room temperature) tap water, as long as your local or state health departments have labeled it as safe to drink. If you're concerned about your water, you may sterilize it to kill germs. Here's how: pour cold tap water into a teapot or saucepan place pot on the stove over medium heat bring water to a rolling boil, and let boil for about a minute let the water cool until it's at room temperature Test to see if the water is cool enough for your baby to drink by shaking a few drops of water on the inside of your wrist. If it stings, it's still too hot. Once water has cooled, don't let it sit longer than 30 minutes before adding it to the formula. Once prepared, the formula is ready to feed to your baby immediately without additional refrigeration or warming. Formula that's been prepared should be consumed or stored in the refrigerator within 1 hour. If it has been at room temperature for more than 1 hour, throw it away. And if your baby doesn't drink all the formula in the bottle, throw away the unused portion — do not save it for later. Formula may be prepared ahead of time (for up to 24 hours) if you store it in the refrigerator to prevent the formation of bacteria. Open containers of ready-made formula, concentrated formula, and formula prepared from concentrate also can be stored safely in the refrigerator for up to 48 hours. How do I warm my baby's bottles? Some babies may actually prefer cold or room-temperature bottles to warm, especially if you start serving them that way from the get-go (which can make things easier for you in the long run). But if your baby does prefer a warm bottle, remember that the microwave can create dangerous "hot spots" in bottles, so you should never microwave formula. Instead, you can: Run the bottle under very warm or hot water for a few minutes. Put your baby's bottles in a pan of hot water. Just be sure to remove the pan from the heat source before placing the bottle in it. Use bottle warmers that either sit on your countertop at home or plug into your car's lighter. Whichever way you choose to heat your baby's bottles, be sure to shake the bottle vigorously. Then test the temperature of the formula by squirting a drop or two on the inside or your wrist before feeding your baby. It should be lukewarm (barely warm) not hot. When should I prepare the bottles? Some parents opt to make a bottle just before each feeding, but many others choose to pre-make and refrigerate enough to use for the day. If you know your baby eats every 3-4 hours, for instance, you can make six to eight bottles to last you all day. If your baby is staying with a caregiver for a long period of time, you may want to prepare just one or two bottles and leave instructions and supplies (bottles, nipples, formula, and water, if necessary) so the caregiver can prepare bottles as needed and not waste any formula. After all, you'll need to throw away any mixed formula that is not used after 24 hours. How long can mixed formula keep in the fridge? You should always refrigerate any bottles you fill for later feedings to prevent bacteria from growing, as well as any open containers of ready-to-feed or concentrate formula. Throw away any mixed formula after 24 hours and any open ready-to-feed or concentrate formula after 48 hours. How long can a bottle keep at room temperature? Discard any prepared or ready-to-feed formula that's been sitting out after 1 hour. If formula is left over, can I offer it again? No, throw away any leftover formula. 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Read More How to Bottle-Feed Your Baby (Video) With a little preparation and practice, you can bottle-feed your baby. Learn how in this step-by-step video. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.