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What Happens If My Baby Drank Old Formula? (PEDIATRICIAN ANSWERS)

Looking after a baby can be exhausting, and when we are exhausted, accidents happen quite easily! If you find that you have accidentally fed your baby their old bottle in the middle of the night instead of the new one sat next to it, you might be worried about what might happen.

What happens if your baby drinks old formula?

Most of the time, nothing will happen if your baby drinks old formula, but there is an increased risk of foodborne illnesses that can lead to vomiting, diarrhea, and in severe cases, dehydration. However, this is rare and mostly what happens is that the formula will not be as nutritious as it was when made fresh.

Read on to find out more about what might happen if your baby drinks old formula, and what you can do if this happens.

Accidentally Feeding Your Baby Old Formula

What Happens If My Baby Drank Old Formula?

It can be so easy to panic after realizing that you have accidentally fed your baby old formula, but you need to try to keep it together and understand that it is not the end of the world!

Yes, feeding old formula to your baby does increase their chance of contracting a foodborne illness, but it is not set in stone that they will get sick. There is a very small likelihood that old formula will make your baby sick.

However, it is still a very good idea to avoid feeding them old formula, just in case it is the one time that they do get sick.

If your baby does contract a foodborne illness from old formula, they will become sicker than an adult would, and the illness will be more severe. Their still-developing immune system is not as strong as yours, and this can make food poisoning that much more harmful.

So while accidentally feeding your baby old formula can make them sick, the chances are that they will not become ill, but you should still keep an eye on them to see if they develop any new symptoms.

What Happens If Baby Drinks 2 Hour Old Formula?

There should be no issues if your baby drinks a 2-hour old formula. The World Health Organization (WHO) states that formula needs to be consumed within two hours of being made, or of liquid formula being opened.

As most formulas are made with a dairy base, being left out for more than 2 hours can increase the risk of the formula spoiling and increase bacteria growth, which could cause foodborne illness.

It should be fine if your baby drinks 2-hour old formula, but if they do not finish it, you should discard any leftovers, as it will not be as safe to drink if left out for longer than this.

Can Babies Get Sick From Drinking Old Formula?

Babies can get sick from drinking old formula, but the chances of this happening are fairly low.

If your baby does become sick from drinking old formula, there are a few different symptoms that they might develop.

These include:


Your baby could start vomiting between an hour and 24 hours after drinking the old formula. Once the old formula or the bacteria has passed out their system, the vomiting should stop.


Diarrhea can start quite soon after your baby drinks old formula. This will present as runny stools, and your baby needing a nappy change more than usual. These stools are often more acidic as well and can cause diaper rashes. 

You would need to change your baby’s diaper immediately after each stool to avoid diaper rashes. Diarrhea, if treated, should stop within a day or two.


Your baby’s immune system would be trying to fight against the bad bacteria, and this could cause a fever. If your baby develops a fever after drinking old formula, you should contact your doctor straight away. 


Dehydration can be difficult to spot, but you really need to keep a lookout for signs of dehydration. Your baby’s skin might appear flush and pale, they would not be passing as much urine, and they might be refusing liquids.

Make sure to contact your doctor immediately if you recognize any signs of dehydration. Dehydration can happen very quickly, especially if they are vomiting or have diarrhea.

All of these symptoms are their little body trying to flush out the bad bacteria, but the symptoms can also cause dehydration, and this can be quite serious.

If your baby displays any of these symptoms and they do not get better in a few hours, you should contact your doctor. Dehydration can be very dangerous for a baby, especially if they are not taking in any new liquids.

What Happens If My Baby Drinks Expired Formula?

You may have mixed up a bottle of formula for your baby, given it to them, and only afterward realized that the actual formula has expired.

There is little risk that your baby will get sick from expired formula, especially if it is powered. The biggest concern with this is that the expired formula will not contain the same nutrients and vitamins that fresh formula would, and your baby would not have gotten these from their feed.

This is because the nutrients begin to break down and disappear after the use-by date, and the formula will not be as beneficial to your baby’s health.

There is an increased risk of illness if the formula has expired and has been exposed to bacteria. There might be mold growth, and this could make your baby quite ill.

It is always best to keep track of the best-by or use-by date on the formula tin and check the formula before using it each time.

What To Do If Baby Drinks Old Formula

If your baby drinks old formula, it is important to keep a close eye on them and see whether or not they develop any new symptoms.

Check to see if they become ill, develop any symptoms of vomiting, diarrhea, or fever. If they do develop any of these signs, then you should contact your doctor immediately for treatment.

Other than that, just try to give them small amounts of liquid every half an hour to ensure that they do not become dehydrated, which is the biggest concern with foodborne illnesses.

They might need a top-up of formula sooner than usual if they have had expired formula, as the formula would not have been as nutritious as it was when fresh. If your baby seems hungry, it is fine to top them up with some fresh formula.

How Do I Know Formula Has Gone Bad?

It is really helpful to know the signs to look for to tell whether the baby formula has gone bad. Here is how to tell if baby formula powder has gone bad, and if formula in a bottle has gone bad.

Baby Powder Formula

It is best to look at the use-by date or the best-by date on the tin of the formula. If you have checked this, and are still unsure as to whether or not the formula is fine to use, look for these signs:

  • The powder is clumping or has hard lumps
  • It has an off, musty smell
  • The lid is bulging or the seal is broken
  • There is discoloration or mold present in the powder

If you notice any of these, it is best to buy a new tin of formula to be safe. Sometimes, a formula can go bad before the best-by date if it is not stored properly, so it is always safer to check.

Baby Formula In A Bottle

It is recommended that you do not feed your baby formula from a bottle that is over 2 hours old. However, if you have not kept track of time properly and are unsure when the bottle was made, there are some signs to look for to see if the milk has spoiled:

  • The formula has an off smell
  • The milk seems to be separating
  • There are lumps in the milk

You should always play it safe and rather not feed your baby formula that you are not sure of, as if it is old, there is a chance that they could develop foodborne illnesses which could make them really sick.

What Should You Do With Old Formula?

There is no point holding onto old formula, as you should not feed it to your baby. You should discard the old formula to ensure that you do not accidentally use it later on.

If your baby goes to daycare during the day, make sure to check that the formula you send to school is not expired either. If the formula is kept at school, set reminders for the daycare to check the expiry date often. Best be safe than sorry!

Giving Your Baby Old Formula

As stressful as it might be, realizing you have fed your baby old formula, you should keep in mind that there is little chance that this could cause them to become sick.

However, it is still worth knowing the symptoms to look for in case they do fall ill. Keep a check on your baby and get rid of any old formula so that you don’t accidentally feed it to them again!

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