In short: Powdered infant formula is not sterile – it can contain small amounts of bacteria such as Cronobacter sakazakii and salmonella. That is why the World Health Organization (WHO) and the NHS recommend making it up with water of at least 70°C, cooling it quickly and using the feed within two hours. Some national agencies advise differently, so also follow your paediatrician’s advice.
Author: Eva Birsa, mum and co-founder of Evitas · Updated: 27 September 2026
Is powdered formula sterile?
No. Many parents don’t know that powdered formula is not a sterile product, even in a sealed tin. According to the WHO it may contain small numbers of micro-organisms that multiply quickly in made-up milk at room temperature. This doesn’t mean formula is unsafe – it means making up every bottle correctly is essential.
Which bacteria can be present?
The WHO highlights:
- Cronobacter sakazakii (formerly Enterobacter sakazakii),
- Salmonella.
Infections are rare but can be serious. Those most at risk are newborns, premature and low-birth-weight babies, and babies with weakened immunity.
How to make up a bottle safely: WHO and NHS steps
- Clean the work surface and wash your hands thoroughly.
- Use a cleaned and sterilised bottle, teat and cap.
- Boil fresh tap water and leave it for no more than 30 minutes so it stays at least 70°C.
- Pour the water into the bottle first, then add the exact amount of powder stated on the pack.
- Close the bottle and shake until the powder dissolves.
- Cool it quickly under a cold running tap and test the temperature on the inside of your wrist.
- Use the feed within 2 hours; throw away any leftovers after the feed.
| Recommendation | Value |
|---|---|
| Water temperature when mixing | at least 70°C (WHO, NHS) |
| Time from boiling to use | no more than 30 minutes (NHS) |
| Using a made-up feed | within 2 hours (WHO) |
| Storing a feed made in advance | fridge at 5°C or below, up to 24 hours (WHO) |
| Leftovers after a feed | throw away |
Why do recommendations differ between countries?
All agencies agree that powdered formula is not sterile and that bottles should be made fresh and used quickly. They differ on water temperature: Germany’s Federal Institute for Risk Assessment (BfR) allows a lower temperature for healthy, full-term babies at home, while France’s ANSES advises preparing the bottle just before the feed. For premature or unwell babies, always ask your paediatrician.
Formula recalls: what to do
Manufacturers occasionally recall individual batches of formula, usually as a precaution because of a contamination risk. If you have a product from a recalled batch at home, don’t use it and follow the manufacturer’s or retailer’s instructions. Recall notices are published by your national food safety authority (in the UK, the Food Standards Agency).
- choose trusted brands and buy from reliable retailers,
- follow the preparation instructions exactly,
- keep hygiene standards high.
How to make it easier
The whole process takes time and care, which is especially tiring at night. The Tommee Tippee Perfect Prep® Pro first adds hot water above 70°C, then cooler filtered water, so according to the manufacturer the bottle is ready in under two minutes. It doesn’t replace hygiene – bottles still need washing and sterilising. Read more about how it works, its pros and maintenance in Tommee Tippee Perfect Prep® Pro: how it works.
Read next
- Tommee Tippee Perfect Prep® Pro: a bottle in under 2 minutes
- Weaning your baby: when to start and first foods
- Sterilisers and bottle warmers and baby bottles
Frequently asked questions
Can I use bottled water?
The NHS doesn’t usually recommend it, because bottled water isn’t sterile and may contain too much salt or sulphate. Use fresh tap water that you boil.
Can I make bottles in advance for the night?
Fresh is safest. If you have to prepare ahead, cool quickly and store in the fridge at 5°C or below for up to 24 hours (WHO).
How long can made-up formula stand?
No more than 2 hours at room temperature. Always throw away leftovers after a feed.
Can I warm formula in the microwave?
No. The NHS warns that a microwave heats unevenly and can burn your baby’s mouth.
Is ready-to-feed liquid formula safer?
Ready-to-feed liquid formula is sterile until opened, which makes it a good option for newborns and travel. Once opened, follow the manufacturer’s instructions.
Sources
- WHO/FAO: Safe preparation, storage and handling of powdered infant formula – guidelines
- NHS: How to make up baby formula
- BfR: Recommendations for the hygienic preparation of powdered infant formula (German)
- ANSES: Baby bottles – how to prepare and store them (French)
This content is for information only and does not replace advice from your paediatrician.
