Can Formula be Reheated? Dangers You Must Know

September 13, 2023
Writen by:  
Cydney Willoughby
Unravel the truths about reheating baby formula: the risks, the myths, and best practices. Ensure your child's health with our comprehensive guide on formula safety and handling.

One common question from parents is whether or not they can reheat formula for their baby. Reaching for and reheating a prepared bottle can be tempting when you’ve got a hungry baby crying to be fed.

Likewise, throwing away baby formula can seem wasteful, especially given the high price we pay for it. Americans in 2022 were paying between $821 and $2,920 a month for formula. So understandably, discarding the leftovers can seem like tossing away liquid gold!

However, once you understand the potential dangers of reheating your baby’s bottle, it becomes clear that it’s not worth the risk. Keep reading to learn how best to plan out your feedings to save yourself from wasting formula and how to keep your baby safe when preparing formula!

Can formula be reheated, or is that dangerous?

The simple answer is no; you cannot reheat formula. Reheating baby formula, even once, can be dangerous because it can create a breeding ground for harmful bacteria, particularly if the formula has been left out at room temperature for an extended period.

This bacterial growth can cause illness or infection in infants, particularly those with weakened immune systems. Therefore, handling and storing baby formula carefully and following the manufacturer’s instructions for preparation and storage is important.

Suppose you’ve made up a fresh batch of formula and don’t feed it to your baby immediately. In that case, it should be stored in the refrigerator and used within the given time frame, according to the manufactures instructions. It is safe to heat formula for this first time that has been safely stored in the refrigerator after preparation, so long as your baby hasn’t begun drinking from it.

It’s worth noting that babies do not need warm milk; it’s just that many prefer it since it makes the formula more similar to the temperature of breast milk. Many parents find that a warmed bottle soothes their baby, especially if they have trouble falling asleep. But it’s also safe to feed your baby room temperature or even cold formula!

What happens if I reheat baby formula?

The number of times you can reheat formula is 0. Whether it’s a liquid or powdered formula, reheating is simply unsafe. As we touched on already, reheated infant formula can contain dangerous bacteria. Moreover, repeatedly warming formulas can degrade essential nutrients your baby depends on for their growth and development.

When babies feed from a bottle, bacteria from your baby’s mouth can enter the liquid. That bacteria, though natural in their mouths, can grow and multiply in reheated formula and be dangerous to your baby’s health. Infant immune systems are delicate and underdeveloped. Even a tiny amount of bacteria can lead to foodborne illness, resulting in diarrhea and vomiting, which can lead to severe dehydration and other complications.

As such, the Food and Drug Administration recommends that parents make as much formula as their baby needs and discard any unused formula after 2 hours.

What is the best way to warm formula?

If you choose to warm your baby’s bottle, it is vital to do so carefully, so here are some best practices for safe formula feeding:

Reheat milk indirectly: A bottle warmer can be very useful, ensuring the formula heats evenly. But no worries if you do not have one; you can also place the bottle in a mug or bowl of hot water to warm it uniformly.

If using a bottle warmer, ensure not to warm the bottle for too long. After more than 15 minutes, bacteria can start to multiply. A good practice is to place the bottle in a bottle warmer on the lowest setting for just a few minutes.

Test the temperature before feeding: Using a thermometer to check the temperature is best. Alternatively, you can place a few drops on your hand or wrist to ensure the formula is not too hot. Your baby’s milk should be served at body temperature, which is 98.6 degrees Fahrenheit (37 degrees Celsius).

Finally, make sure that you don’t microwave formula. It may seem like a quick fix to heat formula in a flash, but it can be dangerous for your baby. In case you weren’t aware, microwaves do not heat liquids equally. Even if you shake or stir the warmed formula, it may still have hot spots within the bottle that can burn your baby’s mouth, throat, or esophagus.

What is the safe way to prepare powdered formula?

Keep your baby healthy by following these preparation steps:

  1. Prepare your space: Clean your preparation surfaces with soapy water.
  2. Wash your equipment: Ensure all your bottles, lids, and containers are completely sterilized. Bacteria can live at high temperatures, so you must boil thoroughly for at least 2 minutes.
  3. Dry your equipment: If you can, air dry your bottle parts on clean towels on your sterilized countertops. If you are not going to use equipment directly, it’s best to cover it with clean towels so that bacteria from the open air don’t contaminate them.
  4. Prepare yourself: Before mixing the formula, scrub your hands with hot water and good soap.

How do I prepare the water for formula?

To prepare formula safely, it’s important to first boil clean tap or bottled water at a high temperature for at least 2 minutes to kill any potential bacteria. After boiling, allow the water to cool below 70 degrees Celsius before mixing it with the formula powder. It’s worth noting that some formulas containing probiotics may require cooling to under 50 degrees Celsius to preserve the good bacteria.

When prepping water, you’ll want to make sure you plan ahead. It can be difficult to wait for the water to reach the right temperature once your baby is crying and hungry. So, remember that it takes around 30 minutes for boiled water to cool!

What are some more formula safety tips?

Because every formula is different, it’s essential to understand the manufacturer’s instructions for your specific product and to prepare the formula safely according to those instructions.

Finally, always remember to follow your doctor’s advice! Some preterm babies may need formula prepared with special instructions to ensure bacteria is not present.

What are some formula-prepping hacks for busy parents?

The reality is that we are all pressed for time! Here are some tips for streamlining formula feeding:

  • You can take liquid or pre-prepared formula from the refrigerator and give it to your baby. Warming is customary but not necessary.
  • You can buy ready-to-feed formula in bottles. These may be more expensive, but all you have to do is open the container and feed. Throw out any unused formula after two hours of opening. The best part, no prep needed!

Can you mix formula ahead of time?

Yes, you can prepare bottles ahead of time. However, most manufacturers recommend this for emergencies only, not as a first choice. The safest method is to prepare the formula fresh right before feeding. Although storing formula in the fridge is relatively safe so long as you take the necessary precautions, it is never as safe as preparing each bottle fresh.

Always read the instructions from the manufacturer for specifics, but generally, you can make a few bottles in the morning, refrigerate them, and heat them later (within 24 hours). If you are going to travel, for example, you will need to make bottles ahead of time and keep them cool during transit.

Once you begin to feed your baby a bottle of formula, you can continue to feed your baby room-temperature formula up until 2 hours from when you started. After that timeframe, throw out any leftover formula.

The critical points to remember here are that after touching your baby’s mouth, the bottle of formula might have bacteria, so it must be used within that 2-hour window or discarded, and it’s best to prepare your formula on the spot rather than ahead of time.

How long can I store liquid formula in the fridge?

You can usually store unused liquid formula that has not yet been heated in the refrigerator for 24 hours; some manufacturers allow for 48 hours. It can quickly spoil if your refrigerator is not at the proper temperature, so it should be kept below 4 degrees Celsius.

How do I know if baby formula has gone bad?

The best way to find out is to check the formula expiration date provided on the package. Labeling the formula container on the day you open it can also be a good idea so you know exactly how long it will last. Similarly, after you prepare bottles for feeding, it is a good idea to mark them with the time and date.

Beyond the expiration date, the color or texture of the liquid formula can tell you if it’s gone off. It should not be lumpy, and any brown or discolored growth around the lid of liquid formula will tell you that bacteria is present. As for canned formula, it should be thrown away if it has any deep dents (large enough that your finger enters it).

If you’re ever unsure, a straightforward method is to smell or taste a few drops of your baby’s formula. Our noses and tastebuds can alert us if the formula has turned.


If you’re a parent who supplements your child’s diet with formula, you’re not alone – millions of parents do the same! But what do you do if your little one doesn’t finish their bottle? Can you reheat it later? Unfortunately, the answer is a firm no – reheating formula is a big no-no and can be dangerous for your baby’s health.

Luckily, there are ways to help you avoid having leftover formula. One thing you can do is to prepare only as much formula as your little one needs to minimize any waste. Another option is to try out liquid formulas, which can be a big time saver.

And here’s a fun fact – your baby may enjoy cold formula, so there’s no need to warm it up if they don’t mind it! So, whether you’re a first-time parent or a seasoned pro, remember – when it comes to reheating formula, it’s always better to be safe than sorry!

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