Can You Reheat Formula?


Formula can at times be difficult to get your hands on, and purchasing it often can add up to quite an expensive purchase, so you may be wondering if you can save the milk that your little one doesn’t guzzle down and reheat it later. 

While this might seem like a convenient idea. It is not a safe one. You should not reheat baby formula under any circumstances.

Why exactly this is, will be revealed throughout this article, along with many other safety tips and information regarding formula. 

How To Safely Prepare Formula

Clean The Prep Area

Make sure that you always thoroughly clean the preparation area and always wash and dry your hands before touching any of the equipment. 

Clean The Bottles

Can You Reheat Formula

Next, ensure that all the bottles you will use are clean, wash them with hot soapy water or in a dishwasher.

If they are new bottles, ensure you thoroughly sterilize them. 


If you have a premixed formula you won’t need to mix it with water.

If you are using liquid concentrate formula or powdered formula then you will require water.

Follow the instructions on the container for the desired quantities of formula and water. 

Use Safe Water

When preparing formula, it is vital that you use safe water. If you have any reservations about the water from the faucet, boil it first.

If you are boiling water, you’ll want to use cold water and gently bring it to a boil.

Once it is boiling you can then let the water cool until it reaches room temperature – you need to use this within 30 minutes. 

Water Then Formula

When you make a bottle, always add the water to the bottle first and then the formula second.

Once you’ve attached the bottle lid, shake vigorously. 

How Long Can Formula Sit Out?

Any formula that has not been kept in a fridge must be used within two hours of it being made.

This is because bacteria will start to grow at room temperature and this will make your baby sick, which nobody wants.

Discard all bottles that have been sat out for longer than 120 minutes. 

If your baby leaves half a bottle, the rest needs to be thrown out after an hour from when they first started drinking.

Bacteria in your baby’s mouth can penetrate through the bottle and contaminate the milk.

If you feed this to your baby later, they will become very sick. 

If you’ve warmed a bottle of milk, you have about an hour where it’s okay to use.

If you surpass this time, the milk will need to be discarded.

Do not put previously warmed formula back into the fridge. 

How Long Will Mixed Formula Last?

You can batch prepare a fair amount of formula as long as it is either used or refrigerated immediately once made, but how long will the refrigerated milk last? 

When you put formula in the fridge you need to transfer it to a closed, tightly covered bottle or container.

You can keep this in the fridge for no more than 24 hours, if you haven’t used it by then, you’ll need to toss it. 

If you have a ready-to-feed formula that you’ve opened, you can store it in tightly closed bottles or containers and refrigerate it.

You’ll want to check the instructions on the bottle as to how long this can be open for, and what to do with leftover milk.

Usually, RTF formulas have around 48 hours of life once opened. 

If you are batch-making formula regularly, it may be worthwhile labeling your bottles with the date and time so you know exactly when each bottle needs to be discarded.

This ensures that you don’t feed your baby unsafe milk. 

Can You Reheat Formula (1)

Can You Reheat Formula?

This is a big no. Once you warm up a bottle it should be used within the hour and if it is not, then it should be discarded.

If you reheat the formula you are really highly increasing the likelihood of bacteria growth in the bottle. 

If you are heating up a refrigerated bottle, you’ll want to run it under hot water.

Swirl this for a couple of minutes. Alternatively, you can also submerge the bottle in hot water until it reaches the correct temperature.

Always check the temperature of the milk before feeding your little one. 

You can also purchase bottle warmers that will do most of the work for you.

However you do decide to warm up your formula just make sure that under no circumstances that you microwave the formula.

Much like it tends to with food, it will heat the formula unevenly, creating hot spots within the milk which will scold your little one. 

If Your Baby Doesn’t Finish Milk Can You Reuse It? 

No. Reusing baby milk will cause your baby to get sick.

The bacteria that grows within the milk is harmful to your little one, so if they don’t finish a feed within the hour, you’ll need to bin any leftovers. 

Once a bottle has been left out at room temperature, once you’ve discarded the milk, it is essential that you thoroughly clean and sterilize the bottle as bacteria can linger in the bottle.  

Traveling With Formula

Since milk quite clearly has a short life, it can be difficult to know what to do if you’re traveling a fair distance because your baby won’t wait to feed until it's convenient for you. 

You have a few options in this instance:

Ready-To-Feed Formula

This formula is super easy, as you can simply take an unopened container and clean baby bottles. When it’s time, just pour and serve instantly. This is a more expensive option though, and your baby isn’t likely to enjoy it if they are used to a different type of formula. 

Powdered Formula

Take clean bottles that are already filled with water with you. When it’s time for a feed you can scoop some powdered formula into the water and then shake and serve

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