New Guidelines for Preparing Formula

I've been educating parents for years on how to properly prepare baby bottles using powdered formula. It's a lot more complex than most people realize! Almost everyone I encounter is unknowingly doing it wrong. I know I was, back when I was a new parent!

But a new study in July of 2025 revealed that the guidelines we've been using aren't sufficient to kill the Cronobacter spp bacteria. There's an excellent article from the Cornell Chronicle, in which they summarize the issue and go over the new recommended formula prep guidelines. I highly recommend that you check it out!

Let me catch you up to speed; essentially, powdered infant formula is not sterile. It can often be contaminated with E. sakazakii, Salmonella, and lead, among other pathogens and harmful bacteria. Milk products also provide an excellent breeding ground for bacterial proliferation.

In order to safely feed it to our babies, we first need to mix it with boiling water. When I was a new mom, I thought these boiling guidelines were only to ensure that the water was clean, so I, like most other parents, disregarded this step. Nope! The purpose is to kill the bacteria in. the. formula.

How Common is it?

This 2025 review found that 1 out of 82 formula samples in the US contained unacceptable levels of Enterobacteriaceae. A study included in this review by Iversen & Forsythe found that 2 out of 82 cans of formula in the US qualified as "defective quality" in the Total Viable Count (TVC) criteria that defines the microbiological quality of infant formula.

It's common enough. We should go ahead and employ safe preparation practices just in case.

Why is This A Big Deal?

Cronobacter contamination can cause septicemia, meningitis and death. Fortunately, cases are rare, with only about 18 cases occurring annually in the U.S.

E. sakazakii is much more common, though exact, recent rates in the US are hard to identify. "Multiplication of E. sakazakii can cause devastating sepsis, particularly in the first 2 months of life. There are high rates of meningitis, brain abscesses, and necrotizing enterocolitis, with an overall mortality from 33% to 80%," according to the aforementioned study.

Who Does This Affect?

High-risk babies have been identified as:

• babies under 2 months of age

• babies who were born premature

• those who are immunocompromised

So What are the New Guidelines?

What we're learning with these recent findings is that just instructing to use "boiling water" isn't enough. The exact temperature of the water is very important, in order to ensure that the bacteria are killed. We need a minimum temperature of 158ºF  (70ºC) to kill Cronobacter and E. sakazakii. Since water can cool so rapidly, and variables in the environment can affect these temperatures, the new guidelines are to heat water to 165ºF (73.8 °C), and then mix it with the powdered formula for a full minute. They recommend stirring or swirling to mix, but you can also shake it if you prefer (please take care not to burn yourself, as this water is very hot to the touch, and pressure quickly builds inside the bottles).

Pro Tip: Using the right tools makes all of this SO much easier! You can get a digital thermometer for a few dollars, which will accurately and instantly tell you the temperature of the water in your bottles. Alternatively, you can get one of those tea kettles with the pre-determined temperature buttons on them, so your water will heat exactly to the temperature you program it to. The benefit of having a digital thermometer is that you can also use it to ensure that the bottle has cooled down to a safe enough temperature to give to your baby, preferably between 98ºF-100ºF (36ºC-37ºC).

Cooling the Bottles

You can choose active or passive cooling. Passive cooling is more effective at killing bacteria, but active cooling takes less time and is more convenient. Active cooling can include running the bottles under cold running water, or placing the bottles in an ice bath. This can take a few minutes, which is preferable if you have a hungry baby waiting for their bottle.

Passive cooling can include leaving the bottle(s) out at room temp until they cool down to a safe temperature to feed Baby, preferably between 98ºF-100ºF (36ºC-37ºC). This can take between 30-60 minutes, depending on the material and size of your bottles, so you may want to confirm with a thermometer before either feeding your baby, or storing the bottle(s) in the fridge for later.

Discard

You want to use the freshly prepared formula within 2 hours of preparing it. But that time cuts down to just an hour once it touches your baby's lips. Any formula remaining in the bottle should be discarded once you're done.

Storage

Formula that hasn't touched your baby's mouth can be stored in the refrigerator for up 24 hours. Be sure to label any bottles that you store, so that anyone encountering them can gauge their freshness and expiration.

Bulk Prep

Since this is such a tedious process and it can take such a long time for the water to get sufficiently hot enough to kill the bacteria, then cool enough to safely feed your baby, it really does make things easier if you can batch prep a whole day's worth of formula in advance. You can prep multiple bottles simultaneously, then store them all in the fridge until it's time for feeding. This is what I recommend, and often what I help families do as a Postpartum Doula.

The Usual Disclaimers

Pathogenic bacteria is not exclusive to formula cans; it's also been found to originate from households, whether from dirty surfaces, utensils, or from care providers skipping hand washing. Please use good common sense and take all the usual precautions to keep the preparation area, bottles, and accessories as clean as possible. Wash your hands before and after. If possible, keep the formula scoop in a clean, accessible place to avoid having to dig for it in the powder.

Alternative Options

• Purchase liquid formula - this is a more expensive option, but this ready-to-use version is sterile and safe to feed directly to Baby, no boiling required.

• Breastmilk is an excellent sterile feeding option! If mother's milk is not an option for your family, consider donor milk. You might check with your local hospitals to see if they have a donor bank. There are also local chapters of organizations like Eats on Feets and Human Milk 4 Human Babies.

  • Remember that breastmilk has entirely different handling and storage rules than formula, because it's a live, antibacterial substance. KellyMom has a great printable guide to reference, but it's a good rule of thumb to just never throw out breastmilk. It's often still safe for consumption, and if it's not, there are lots of great topical uses for breastmilk!

Simple Directions, Please!

I've created a handy infographic with all the details in one place. This would be great for you to put on your fridge, or keep saved to your phone for quick reference. It would also be good for you to share with any friends and family who bottle-feed!

Updated Guidelines for Safe Formula Preparation (2).pdf

Download PDF • 1.91MB

I hope this helps! Happy parenting!

Angel Mattes

Birth & Postpartum Doula

Lactation Educator

Child Passenger Safety Technician (CPST)