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Why does baby formula need to be thrown out after one hour?


Any parent who formula feeds their infant has likely heard that unused prepared formula should be thrown out after 1 hour. But the formula label and most articles you find on the topic don’t usually get down to why this is the case. So, if you’ve ever wondered why infant formula needs to be thrown out after 1 hour, we’ve got answers.

How to make infant formula

First, let’s review a little about exactly how to mix and store infant formula. Especially if you’re a first time parent or are switching from breastfeeding to formula feeding, it’s helpful to review this information a few times to make sure you’re getting each step right. Remember, measuring infant formula wrong can cause health problems for babies, so it’s always better to double check yourself.

  1. Make sure to sterilize bottles and nipples before using them for the first time. This can be done by putting them in water at a rolling boil for 5 minutes or using a bottle sterilizer. After you’ve done this once you can just wash bottles in the dishwasher or in hot water with soap after each use.1
  2. Wash your hands well and clean and sterilize the area where you will be preparing the bottle.2
  3. Mix formula with water according to the directions on the formula container.2,3,4
  4. It’s safe for babies to have cold, room temperature or warm formula- whichever they prefer is best! Just remember, if you’re going to warm the bottle, use a bottle warmer or place the cold bottle in a bowl of warm water or run the bottle under warm water from the tap. Never use a microwave and be sure to test the formula before giving it to your baby to make sure it’s not too hot.1,2

How long can baby formula sit out?

It’s important to know that if you’re switching from breastfeeding to infant formula feeding that some of the storage recommendations are different between the two. Here are the basics before we jump into the “why”.

  1. After you prepare formula, any formula that is left over in the bottle your baby drank from needs to be thrown away. This is because that bottle now has bacteria from your baby’s mouth in it, which means it might be contaminated with germs.2
  2. There are different recommendations for how long formula you’ve made (that’s not in the bottle your baby drank from) can be left out at room temperature before it needs to be thrown away. The American Academy of Pediatrics (AAP) says that formula out for longer than 1 hour at room temperature should be thrown away. They also state that formula that has been out for 1 hour or less can safely be stored in the refrigerator.3 The Centers for Disease Control and Prevention (CDC) says formula does not need to be thrown away until it’s been out at room temperature for more than 2 hours. According to them, if it’s been out for 2 hours or less, it can safely be moved to the refrigerator for storage.2 Be sure to check the instructions on your specific formula container and when in doubt, be cautious and stick to the 1 hour rule.
  3. Both the AAP and the CDC agree that formula made from powder can be safely stored in the refrigerator for up to 24 hours. After that it should be thrown away.2,3
  4. Unlike breast milk, formula cannot be frozen.5
  5. If the formula has been heated, it has to be thrown out and cannot be refrigerated.5

So why does formula need to be thrown out if it’s not used?

Although US infant formula meets strict criteria set by the Food and Drug Administration (FDA) for safety and quality, just like any food that us adults eat, it is not sterile. That means that there is a risk it could have some bacteria in it.6

This is why it’s so important to follow all the cleaning and sterilizing instructions when making formula and washing bottles. As you know, germs can come from anywhere, so you don’t want to add any risk by not washing your hands or the bottles, where germs can also live.

Right now you might be thinking, what is it about one hour if any type of formula could already have bacteria in it from the start? Well, bacteria can really thrive and multiply in certain conditions. And for formula this condition is being kept at or above room temperature for too long. So it’s best to get rid of the formula or refrigerate it before this has a chance to happen.6

Taking all the recommended precautions when preparing formula is similar to how you carefully handle chicken— making sure it’s cooked all the way through— or wash your greens before making a salad.

One important way to help reduce any risks in preparing formula is to make each bottle right before you give it to your baby.4

Storing baby formula containers

There are a few other important things to know about storing infant formula to keep it fresh and safe. Once a formula container is opened, make sure to store it in a cool dry place, but not in the refrigerator. It should never be kept somewhere outdoors, like in a car where the container can get hot.

Baby formula expiration date

Most formula containers need to be used within one month of opening, so write the date you open it on the lid to keep track of this. And check the “use by” date on the container- never use a formula after this date has passed.2

Certain babies are at higher risk for getting sick from bacteria in formula, so it’s especially important to carefully follow instructions for making and storing formula for these infants. This includes babies who are less than 3 months old, have a problem with their immune system, or were born prematurely.2,6

Take-home message on why baby formula needs to be discarded

While infant formula is highly regulated and monitored, just like other food products, it is not sterile. This means there is a risk that bacteria may be in the container, which can cause health problems if the container is not stored, prepared, and handled the right way. By following instructions for cleaning your hands, sterilizing and cleaning bottles, not keeping formula at room temperature or stored in the refrigerator for longer than recommended, and always following the manufacturer’s directions on the label, you can reduce the chances of your baby being exposed to bacteria.


1- Formula feeding FAQs: preparation and storage | KidsHealth

2- Infant formula preparation and storage | Centers for Disease Control and Prevention

3- Are you preparing your baby’s bottles correctly? | American Academy of Pediatrics

4- Feeding your infant: how to prepare and store baby formula | Cleveland Clinic

5- How long is formula good once mixed? And other questions about formula | Healthline

6- Preparation and handling of powdered infant formula: a commentary by the ESPGHAN committee on nutrition | Journal of Pediatric Gastroenterology and Nutrition

The content on this site is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment. Discuss any health or feeding concerns with your infant's pediatrician. Never disregard professional medical advice or delay it based on the content on this page.

Meet the Author

Morgan Leafe

Morgan Leafe, MD, MHA, is a medical writer and editor who is double board certified in Pediatrics and Clinical Informatics with 14 years of clinical experience caring for pediatric patients and their families. She specializes in writing both patient-facing and clinician-facing material.

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