Guide To Safely Reheating Baby Formula - And Why It Matters

Understanding how to safely reheat baby formula is knowledge every parent should have. In between navigating daycare drop-offs, nap schedules and your baby’s hunger and temperament, there’s bound to come a time when bottles need to be prepared on the go.

In Australia, guidelines from trusted bodies like the National Health and Medical Research Council (NHMRC) and the Australian Breastfeeding Association (ABA) are clear: formula should be prepared fresh for each feed whenever possible. But what happens when life gets busy, your baby doesn’t finish a bottle, or you’ve prepared a feed in advance? Can you reheat formula? And if so, how can you do it safely?

From bacterial growth risks to temperature control and safe warming methods, below we cover everything you need to know about reheating baby formula while ensuring each feed is nutritionally sound.


Baby Formula Basics

Baby formula is packed with the essential nutrients that babies need for their growth and development. But it's not just about what's in the formula – how you handle and prepare it is just as important. Proper handling and preparation of baby formula is crucial to ensure your baby's health and safety. This includes understanding how to heat, reheat, and store formula correctly. Let's dive into the basics of heating baby formula.


Baby Formula Safety Basics in Australia  

Australia is known for its warm and sunny weather, which is great for beach days but can also create an environment for bacterial growth to thrive, particularly when it comes to perishable liquids like baby formula. This is why we have clear guidelines for ensuring infant formula is prepared, stored, and transported correctly.

The NHMRC’s infant feeding guidelines emphasise that formula should be prepared fresh for each feed, whenever possible, and that hygiene is key. Here are the top safety tips to remember.

When preparing baby formula:

  • Always wash hands before preparing formula and ensure that formula is prepared in a clean area.

  • Clean and sterilise bottles, including teats, lids, and all accessories before every use. Even small amounts of leftover milk can harbour harmful bacteria.

  • Follow the formula tin’s instructions precisely. Add cooled boiled water to the bottle first, followed by the correct ratio of powder.

  • Always test the formula temperature on your wrist before feeding. It should be lukewarm, not hot.

  • If not feeding straight away, store it in the fridge at 5°C or below.

When transporting baby formula:

Ideally, infant formula should be prepared at the destination to avoid risks during travel. However, if this isn’t possible:

  • Leave the feed in the fridge until immediately before transporting.

  • Keep prepared formula cold (below 5°C) using an insulated cool bag with ice packs.

  • Use within two hours once the feed is taken out of refrigeration.

  • Rewarm formula at destination (no more than 15 minutes).

No matter when or where you’re feeding your baby, all equipment should be carefully sterilised before use. Sterilisation is crucial for babies under 12 months, as their immune system is still developing. NHMRC guidelines recommend these methods of sterilisation:

  • Boiling: Fully submerge all cleaned items in boiling water for at least 5 minutes, ensuring no air bubbles are trapped. Turn off the heat and allow it to cool before removing equipment from the water. Air dry on a clean surface.

  • Steam sterilisation: Use an automatic electric steam steriliser or microwave steam system, following the manufacturer’s instructions carefully.

  • Chemical sterilisation: Use food-grade sterilising tablets or solutions, ensuring all items are cleaned thoroughly beforehand and fully immersed for the specified time.


Can You Reheat Baby Formula?

Now, to the main question: can you reheat formula? The simple answer is yes, but it comes with a caveat. You can rewarm formula if it has been properly stored, but you should never reheat formula that your baby has already started drinking from. The reason for this is that bacteria from your baby's mouth can get into the bottle and multiply, even if the bottle is stored in the fridge. Reheating won't kill the bacteria, and it could potentially make your baby sick. So, if your baby doesn't finish a bottle, it's best to discard the leftover formula.

If the formula bottle has been carefully prepared following the direction on the pack, properly stored and untouched by your baby, the best method for reheating is a warm water bath. Place your filled bottle in a bowl of warm water or run it under a warm water tap. Test the temperature on your wrist, ensuring it is lukewarm to the touch and not hot. Bottle warmers are another option, which can be handy when you’re out and about or unable to access hot water – just be sure to follow the usage directions carefully. We recommend to consult a paediatrician for any questions or concerns.

Warning: Never use a microwave to reheat baby formula. Microwaves can create hot spots that may burn your baby’s mouth or throat. Uneven heating makes it an unsafe method for reheating, even if the bottle feels cool on the outside.


How Long Does Formula Last Once Made?  

In general, if baby formula is made and left at room temperature, it should be used within 30-60 minutes. This includes once your baby begins feeding. If your baby doesn't finish the feed within one hour, you should discard the leftovers. This is because bacteria from your baby's mouth can multiply rapidly at room temperature. However, the time limit may vary depending on the product you’re using, so always check the label or ask your paediatrician if you’re unsure. You should discard any formula that smells sour, looks curdled or discoloured, or has a strange texture. When in doubt, it’s safest to throw it out.


How Long Can Formula Stay in the Fridge?

If you've prepared a bottle of formula but your baby isn't ready to eat yet, you can store the formula in the fridge for up to 24 hours. Ensure the bottle is properly sealed with a lid protecting the teat, and store it at the back of the fridge where it is coldest. Fridge temperatures should be set below 5°C. When transporting formula, keep it cold (below 5°C) using an insulated cool bag with ice packs. Different guidelines may apply for different types of baby formula, so be sure to always check the label or seek advice from your paediatrician.


Quick Tips for Safe Formula Handling & Feeding  

Now that we’ve answered the burning question: can you reheat formula? Let’s recap the top safety tips.

  • Always wash your hands when preparing formula.

  • Use sterilised equipment.

  • Adhere to time guidelines (1 hour at room temp, 24 hours stored in fridge).

  • Store below 5°C.

  • Use a warm water bath to reheat.

  • Never use a microwave for heating baby formula.

  • If formula appears ‘off’, your baby has drunk from the bottle, or you’ve lost track of time, discard and start fresh.


Where to Find More Resources 

If you’re ever in doubt when it comes to formula preparation and storage (or any parenting questions for that matter!), trusted online sources in Australia include the Raising Children Network and Government sites linked to the Department of Health. In regard to Bubs baby formula products, you can see our FAQs here. We also recommend to consult a healthcare professional if you have any questions or concerns about feeding your baby.