How Long Can Formula Stay Out at Room Temperature?

If you're feeding your baby formula, you might have some questions about safe storage. Here's what you need to know about keeping formula at room temperature.

By Sarah Cottrell

Updated on July 1, 2024

Medically reviewed by Natalie D. Muth, M.D.

Infant formula is a nutritious and convenient food that supports healthy growth for babies. But when your baby doesn't finish their bottle, or when you're bringing formula somewhere on the go, you might have an important question: How long can formula stay out at room temperature? Along those lines, can you reuse a bottle of formula if your baby didn't finish it? Here, experts weigh in on formula safety standards you need to know.

A Caucasian parent scoops infant formula for feeding their baby into a bottle. — RyanJLane/Getty Images

How Long Can Formula Sit Out?

Baby formula is susceptible to spoilage, just like human's milk or cow's milk. For this reason, it can only remain at room temperature for two hours after mixing, or one hour after a baby has begun to feed. After that, caregivers should discard any leftover formula by pouring it down the sink.

Abrie McCoy, a baby feeding expert and a certified lactation consultant (CLC) with SimpliFed, explains that when a baby drinks from a bottle, the combination of their saliva and a warm temperature introduces the opportunity for bacteria to grow, creating a ripe chance of spoiling the formula and potentially making a baby sick if they drink from it later.

It's important to note there's no real way to know if the formula has begun to grow bacteria that can make a baby sick. For this reason, caregivers should always toss any prepared formula that has been out for two hours at room temperature even when it's been untouched.

Can Prepared Formula Stay in the Fridge?

One popular method of mixing formula is to do batch mixing, which is when a caregiver mixes up a full day's worth of formula and keeps it in the fridge. Batch mixing is convenient for busy families, especially if a baby goes to daycare. But is it safe?

"Formula can be refrigerated for 24 hours after preparation, but before the infant feeds from a bottle containing the formula," says Leslie Sude, M.D., a pediatrician affiliated with Yale Medicine in New Haven, Connecticut. "After the baby drinks from the bottle, if there is any excess formula in the bottle, it should be discarded." Again, explains Dr. Sude, "The germs in baby's mouth can mix with the formula and cause contamination."

Tip for Batch Mixing Baby Formula

Try mixing bottle sizes that best match your baby's different appetites throughout the day. For example, if your baby likes to have a big bottle in the morning and a smaller one in the early afternoon, store bottles with those differing amounts to make sure they get used.

But it's also a good idea to use responsive feeding. That means learning your baby's cues for hunger and being full and responding appropriately. So, even if your baby tends to eat a certain volume of formula with each feed, pay attention to their cues that moment and don't force them to finish the bottle if they don't want to.

How Long Is a Bottle Good for If Your Baby Drinks From It?

If your baby has been drinking from a bottle and there is any formula left, that formula is only considered safe for up to one hour after your baby has started drinking. Always discard any leftover formula.

How Long Is Formula Good for After It's Opened?

Once a container of formula has been opened, it should be used within one month and stored in a cool and dry place. "After this timeframe, the formula should be discarded," says McCoy. "Writing the date on the lid can help you keep track."

Always follow the manufacturer's instructions for properly storing unused, open baby formula to keep it safe. Dr. Sude says the following steps can be used to keep your formula safe from spoilage:

Store unopened infant formula containers in a cool, dry, indoor place—not in vehicles, garages, or outdoors
Once a container of infant formula is opened, store it in a cool, dry place with a tightly closed lid
Do not store unprepared formula in the refrigerator

Also discouraged is freezing mixed formula. Even if you mix a big batch of baby formula that has not been contaminated with your baby's saliva, which could introduce bacteria and other germs, the product is not designed for freezing and can cause components to separate.

Can You Reheat Formula?

Formula doesn't have to be heated, but some parents and babies may prefer it that way. If you'd like to warm it up, never use a stovetop or a microwave, as this could affect the nutrition profile of the formula or get too hot and burn your child.

According to the Food and Drug Administration (FDA), the best way to warm mixed baby formula is to place the bottle under warm running water for a minute or two. Gently swirl the bottle to prevent hot spots, and then test the formula temperature by dabbling some on the inside of your wrist.

Once formula has been heated, experts advise against reheating it.

How Long Does Unopened Baby Formula Last?

Like all food items, unopened formula has an expiration date. That's typically about a year. Make sure to check the "Use By" date when shopping for formula (and before preparing it!) and never use formula after that date.

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