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Formula Feeding FAQs: Preparation and Storage

Whether you plan to formula feed your baby from the start, want to supplement your breast milk with formula, or are switching from breast milk to formula, you probably have questions.

Here are answers to some common questions about formula feeding.

Do I Need to Sterilize My Baby's Bottles?

Before the first use, sterilize nipples and bottles in boiling water for 5 minutes.

After that, you don’t have to sterilize your baby's bottles and supplies each time you feed your baby. Do wash bottles and nipples in hot, soapy water in a basin that is only used for cleaning baby bottles (or in the dishwasher) after every use. You can get a store-bought countertop or microwaveable sterilizer, but it’s not necessary.

After you clean your baby’s bottles, let them air dry on fresh paper towels or a clean towel. Don’t let them touch the counter or the sink where germs could contaminate them.

How Do I Prepare My Baby's Bottles?

Carefully follow directions on the label when preparing formula. Most store-bought formula comes in three basic forms:

  • powders that you mix with water
  • concentrates, which are liquids that you dilute with water
  • ready-to-use (or ready-to-feed) liquids that can be poured right into bottles without adding water

Do not add more water than directed or use formula past its expiration date.

To make formula from powder or concentrate: 

  • Make sure the counter where you are making the formula is clean.
  • Wash your hands well. 
  • Make sure the bottles and nipples are clean.
  • To mix powders or concentrates, use clean room temperature tap water. If you have a well, test the water to see if it’s safe before using it to mix infant formula.
  • If you are not sure about your tap water, call your local health department. If your tap water is not clean or your baby has a weak immune system, boil the water for at least 1 minute to kill germs. Let the water cool to room temperature before using it to mix formula. You also can use bottled water. Talk to your doctor if you’re concerned that your water is not safe.
  • Once prepared, the formula is ready to feed to your baby right away without refrigeration or warming. Feed your baby or store the prepared formula in the refrigerator within 2 hours.

If your baby is younger than 2 months old, was born early (before 37 weeks), or has a weak immune system, take extra precautions to avoid germs that can cause infection: 

  • If you can, use ready-to feed formula or concentrated liquid formula. They have less risk of being contaminated with germs.
  • If making powdered formula or concentrated liquid formula:
    • Boil the water and let it cool for 5 minutes.
    • Carefully pour the measured amount of hot water into the clean bottle.
    • Add the amount of powdered formula or liquid concentrate indicated on the container.
    • Shake to mix.
    • Cool the bottle so it doesn’t burn the baby. Hold the bottle under cool water. Be sure no water gets into the bottle or on the nipple.
    • Put a few drops of formula on your wrist before feeding your baby. It should feel lukewarm (barely warm) and not hot.

How Long Can a Bottle Keep at Room Temperature?

Throw out any prepared or ready-to-feed formula that's been sitting out for 2 hours or more, or within 1 hour from start of feeding.

Can I Save Leftover Formula to Give to My Baby Later?

No, throw away any leftover formula. Harmful bacteria can multiply since the last feeding, which could make your baby sick.

Can I Prepare Formula Ahead of Time?

Some parents make a fresh bottle just before each feeding. But many parents make and refrigerate enough formula ahead of time to use for the day. If you know your baby eats every 3–4 hours, for instance, you can make 6 to 8 bottles to last you all day.

If you prepare formula ahead of time, store it in the refrigerator. You can use pre-made formula for up to 24 hours. Open containers of ready-made formula, concentrated formula, and formula prepared from concentrate can be stored safely in the refrigerator for up to 48 hours. Do not store unmixed powder in the refrigerator.

How Do I Warm My Baby's Bottles?

You don’t have to warm formula before feeding, but some babies may prefer it. To warm bottles, you can:

  • Run the bottle under very warm or hot water for a few minutes. Be careful not to let the running water get in the bottle or on the nipple.
  • Put your baby's bottles in a pan of hot water. Be sure to remove the pan from the heat source before putting the bottle in it. Don’t let the water get in the bottle or on the nipple.
  • Use bottle warmers that sit on your countertop at home or are portable.

Never use the microwave to warm bottles. It can create dangerous "hot spots" in bottles that can burn your baby’s mouth and throat.

Before feeding your baby a warmed bottle, shake it. 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.

For more on how to safely prepare and store baby formula, visit:

Reviewed by: Melanie L. Pitone, MD
Date Reviewed: Jan 1, 2024

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