Questions about infant milk safety

Powdered infant milks are not sterile and they may contain harmful bacteria. However, if milks are made up appropriately for infants, they should be safe. Salmonellaand Cronobacter sakazakii(previously known as Enterobacter sakazakii)are the organisms of greatest concern in infant formula and a range of Cronobacterspecies can be present in powdered infant milks. Powdered infant milks contaminated with Cronobacter sakazakii orSalmonellahave been the cause of infection in infants. Cronobacter sakazakiiis regarded as an emerging opportunistic human pathogen. It can be found ubiquitously in the environment, in the human and animal gut, and in foods. The widespread distribution of the bacterium suggests that, in healthy infants, consuming small numbers of the bacteria in powdered infant milks does not lead to illness. However, younger infants are more susceptible to infection than older infants, and the neonates at greatest risk are pre-term or low-birthweight infants and those who are immunocompromised. Whilst the occurrence of infections with Cronobacter sakazakiiis rare, the prognosis for those infected is poor and infection can cause meningitis, necrotising enterocolitis and bacteraemia. There are nearly 2,000 strains of the Salmonellabacteria that can cause illness in humans. Symptoms include diarrhoea, fever and vomiting, and infection can cause serious illness in infants. There have been recent widespread contamination of infant formula with Salmonella in Europe leading to the hospitalisation of infants and a global recall of products.

For a full discussion of the bacterial contamination of powdered infant formula see the resource ‘Bacterial contamination of powdered infant formula: what are the risks and do we need to review current instructions on safe preparation?’ which can be accessed here

Food Standards Agency (2005). Guidance for Health Professionals on Safe Preparation, Storage and Handling of Powdered Infant Formula. Available at:

Food Standards Agency, (2013)


Guidelines for parents and carers on making up milks safely can be found at

Unicef UK Baby Friendly and Start4life guidance at Guide to bottle feeding leaflet – Baby Friendly Initiative (

The NCT also has a factsheet for parents – Using infant formula: Your questions answered – available from

The Department of Health recommend that the safest way to make up feeds from powdered infant formula (PIF) when away from home is to make the feed up freshly using previously boiled water stored in a vacuum flask. The boiling water should kill any bacteria present in the flask. The feed can then be made up in a sterilised feeding bottle when needed, using PIF pre-measured into a small, clean, dry container and the correct amount of boiled water from the vacuum flask. The Department of Health state that vacuum flasks, if full and securely sealed, will keep the water temperature above 70˚C for several hours (Formula milk: common questions – NHS (

We have tested a 17.5oz (500ml) vaccum flask and a 33oz (1000ml/1 litre) vacuum flask filled with boiling water. Both were stainless steel flasks. The flasks were tested filled with boiling water, and the smaller flask was also tested when smaller volumes of water were used. This is because it has been reported that some families take just the amount of water they need for one feed in a flask, and it is important to note how quickly smaller volumes of water cool.

The thermos flasks were both warmed for 1 minute with boiling water before use and the flasks were stored at an ambient temperature of about 19oC. The tests were conducted three times, with each time test completed on a freshly stored batch of boiling water.

The table shows the results for a 500ml flask and a 1litre flask. Please note these are just estimates made by us in a domestic kitchen, and others may find they get different readings depending on types of flasks and thermometers used.

The 10oz flask of water was also tested at 2 hours and 30 minutes and the temperature had dropped to an average 68oC. This suggests that if smaller volumes are used, a minimum of 10oz of water should be carried in a flask, and that water should be used within 2 hours.

Smaller amounts of 5oz will only remain at the correct temperature for about an hour.

A full flask of water securely sealed as suggested by The Department of Health remains at >70OC for at least 3 hours, and in our tests was still above 70°C after 4 hours.If a 1 litre flask is filled with boiling water, it is likely that the water remains at above 70°C for at least 7 hours. This provides an option for parents who want to make up bottles of milk on longer outings, or during the night.


Care must be taken to avoid scalds when handling hot water, especially when a full litre flask of water is being used. Great care must be taken that the milk given to the infant is at the correct temperature. Run the prepared bottle of formula under a cold tap to cool, shake vigorously and always test the milk temperature on the inside of the wrist before offering to a baby.


We have been asked whether it is possible to make up powder with smaller volumes of hot water to kill any bacteria present and then top up the bottle with cool, boiled water. There is however no evidence to suggest how much hot water is needed to mix with the powder to ensure that the powder has sufficient exposure to water at 70°C, and therefore standard advice remains to add the powder to the full volume of hot water, shake thoroughly, and then cool.

Formula preparation machines are marketed as being a sterile and convenient method of preparing formula feeds at the correct temperature for consumption, within minutes. Whilst the scale of use of these is not known, recent research at Swansea University suggests that just over 50% of families are using preparation machines (personal communication, Amy Brown).

In the UK, the most popular formula preparation machine available at high street retailers is the Tommee Tippee Perfect PrepTM Machine. This machine claims to “prepare a fresh bottle at just the right serving temperature within 2 minutes”. The machine uses a two-step process to prepare the feed. In the first step the machine dispenses a ‘hot shot’ of water directly into the bottle. The user then has two minutes to add the PIF, place the holding cap on the bottle, shake to mix and return the bottle to the machine. In step two, cold water is added by the machine to make up the selected feed volume to a comfortable temperature to feed immediately.

Whilst research into the safety and efficacy of the Perfect PrepTM Machine has been carried out by the manufacturer, this is not currently in the public domain and the manufacturer has declined to release it citing business competition reasons. Mayborn Group Ltd, who produce Tommy Tippee brand products, have said:

“Our Perfect Prep product has been tested by an independent laboratory that validated that the ‘hot shot’ of water addressed the (E.Sakazakii) species of concern. The laboratory used was Intertek Testing Services (UK) Limited. The filter we use is not a standard water filter, such as the ones you might find in a Britta system – it’s an antibacterial filter. We have independently validated the removal of bacteria that may be present in water, and we have done this test in extreme circumstances, dosing the water with significantly higher levels of bacteria than typically found in water supplies, so we can be truly confident of the filter efficiency. Validation was carried out by Intertek Testing Services (UK) Limited.”

 However, unpublished university-based research which investigated the efficacy and temperature profile of the Tommee Tippee Perfect PrepTM Machine using PIF inoculated with known amounts of Cronobacter sakazakii has suggested that, whilst the machine’s hot shot of water dispensed onto a small volume of powder was able to eradicate more than 95% of the bacteria, it failed to reduce their numbers to an undetectable level. Whilst the machine produced water for the ‘hot shot’ at a temperature higher than the 70ºC stipulated in current guidelines, the temperature fell to around 60ºC after two minutes. Furthermore, when PIF was added at 30, 60 and 90 seconds after the ‘hot shot’, the temperatures in the bottle were only maintained for around five seconds before they fell again to between 52.5ºC and 55.5ºC.

This research showed that, depending on when the PIF is added, the water temperature may be too low to effectively eradicate all bacteria present. The volume of the initial hot shot of water used for a 4oz feed is about one fluid ounce, and it is questionable whether this small volume of water can adequately make contact at the right temperature with the amount of PIF added. The research suggests that this volume of water is insufficient to maintain a temperature of greater than 70ºC for the duration of the two-minute window recommended for the addition of PIF. This data has not been published in a peer-reviewed journal and therefore can only be considered as contributory evidence at the present time (First Steps Nutrition Trust, personal communication).

The Food Standards Agency made the following comment when asked about the safety of these formula machines in 2014:

“The issues we have with it are, although it states it dispenses a ‘hot shot’ at 70ºC to kill bacteria that potentially could be in the powder, the reality (if you watch the TT advert) is that the amount of hot water used is very small, and once this is dispensed into a cold bottle/cold powder the heat will be quickly lost (more so than when preparing a full bottle with cooled, boiled water to >70ºC), so we would be interested to see whether TT have done any validation to see what temperatures the hot shot/powder combo actually reaches (and whether this is enough to destroy any bacteria).The other issue, is that the rest of the bottle is then topped up with cold water, which TT state is filtered to remove impurities. Again we would be interested to know whether it has been validated that the TT filter removes potential bacteria in the tap water (as this won’t previously have been boiled). At present the Food Standards Agency would still advocate the use of our Best Practice Guidance, to use cooled, boiled water at >70ºC to make up infant formula.

(Email communication between Francesca Entwhistle (Unicef UK Baby Friendly) and Lorna Rowswell at FSA. February 2014)

The Food Standards Agency have not issued further information, but the Food Safety Authority in Ireland recently made the following statement on its website:

‘The FSAI does not recommend the use of automatic machines to prepare bottles of powdered infant formula because there is insufficient data available to verify the safety and efficacy of these machines. The FSAI continues to recommend the use of cold tap water that has been boiled once and then cooled for no longer than 30 minutes to >70°C to prepare feeds from powdered infant formula’


Some instant hot water taps are marketed as a convenient way to make up infant formula milk. When instant hot taps are used to make up infant formula, boiling water will be dispensed directly into a bottle. Current advice to leave boiled water to cool for no more than 30 minutes when making up formula milks is based on 1 litre of water being boiled in a kettle and left to cool in the kettle, with the aim that the water is still at a temperature of 70˚C or above when the powdered infant formula is added.

In order to achieve the required temperature of 70°C or above when using a hot tap, we have tested temperatures using one type of hot tap in a domestic kitchen as a guide. We tested the water temperature after it had been added to the bottle and after 5, 10 or 15 minutes. An 8oz (240ml) baby bottle was used and water added in ounces as recommended for making up feeds for different ages of babies. We put the lid on the bottle after adding the water.

Our conclusions from this are that if using a hot tap to fill the bottle, the powdered infant formula should probably be added:

  • Immediately if volumes of 2-3oz (60-90ml) are being made up
  • After no more than 5 minutes for volumes of 4oz-5oz (120ml-180ml)
  • After no more than 10 minutes for volumes 6oz-8oz (210ml-240ml)

These times are just a guide and it is likely that other hot taps might provide water at different temperatures.

Whichever tap is used, care is needed when filling the bottles not to scald, particularly if you bend down to the right level to see the bottle markings to add the correct amount of water.

All of the results from our temperature testing can be found in our statement ‘Making up bottles of infant formula from hot taps and baby kettles’ available on the infant milk safety section of our website:

Baby kettles are marketed as being a safe and convenient method of keeping boiled water at ‘the perfect temperature’ for preparing powdered infant formula.

Baby kettles boil water like a standard kettle, and some may then ‘speed-cool’ the boiled water to 70 or 40˚C, or keep it heated at a set temperature for making formula later. The manufacturer’s instructions on at least one brand of baby kettle that we know of are to use water at 70˚C when preparing infant formula.

The NHS advises that water should be at least 70˚C when used to prepare powdered infant formula to kill any bacteria present in the formula. Water maintained at 70˚C is likely to cool below 70⁰C being poured into a bottle and is therefore likely to be less than 70⁰C when the powder is added to the bottle. Using water at a lower temperature increases the likelihood that the water temperature may be too low to effectively eradicate any bacteria that may be present in the powder.

The NHS also advises that fresh water should always be used when preparing powdered infant formula. Repeatedly boiling water may increase the concentration of elements in the water to undesirably high levels. Baby kettles which are designed to keep water hot for long periods of time may repeatedly boil the water to maintain the temperature, thereby concentrating elements in the water.

The convenience of this type of kettle is questionable, as users are still required to sterilise all feeding equipment and wash surfaces and hands before preparation and accurately measure and add the powdered formula to the feeds. The only benefit to parents appears to be the time-saving associated with not having to wait for water to boil and cool before the powdered formula can be added. There is no publicly available research to confirm that baby kettles are safe to use for the preparation of powdered infant formula so applying the precautionary principle, we would not recommend their use. Instead, we recommend that all infant formula is made up according to NHS guidance.

Guidelines for parents and carers on making up infant milks safely can be found at:

 NHS Bottle feeding Advice

Guide to Bottle Feeding (

The NCT also has a factsheet for parents –

NCT Using infant formula: your questions answered

One popular rapid cooling device is the Nuby Rapid Cool flask, which the manufacturers state is designed to cool freshly prepared infant formula to a temperature suitable for feeding in minutes. The manufacturer recommends adding water to the flask at a temperature of around 100⁰C, before adding the appropriate amount of powdered infant formula. The manufacturer’s advice to use water at a temperature of around 100⁰C is acceptable from the perspective of killing bacteria in the powdered formula, although it may also modify some proteins which could impact on how the infant formula tastes. While it will kill any probiotic bacteria in formula containing these as an added ingredient, probiotics have no proven benefits for infants when added to infant formula and the priority when reconstituting powdered infant formula should always be optimising microbiological safety rather than maintaining any live bacteria.

Caution is always required when using boiling water, particularly where bottles or flasks are narrow at the top to avoid any risk of scalding.

One concern with the Nuby Rapid Cool is that it adds an extra step/container to the preparation process which represents an additional risk of microbial contamination. However, sterilising the flask (using NHS recommended sterilisation techniques) after every use would minimise this risk.

It should be noted that the manufacturer’s website states that the device requires at least 3 hours to cool down before the next use. As many young infants will demand a feed more frequently than this, if the device is to be used for every feed it would be necessary to buy multiple products.

It is important that powdered infant milk is made up according to NHS guidance. Guidelines for parents and carers on making up infant milks safely can be found at:

NHS Bottlefeeding Advice

Guide to Bottle Feeding (

The NCT also has a factsheet for parents –

NCT Using infant formula: your questions answered

Self-sterilising bottles are designed to be sterilised in a microwave without the need for any further equipment. MAM self-sterilising bottles have a screw off base which is used for sterilisation. The manufacturers instructions are to wash the bottles then to put tap water in the screw off base, assemble the bottle without screwing together, in a specific order on top of the base. The assembled bottle should then be placed in the microwave for 3 minutes and must be left to cool after sterilisation for at least 10 minutes before being used to make up a feed. There is no specific national guidance on the use of self-sterilising bottles. We have asked the manufacturer for information on the safety of their self-sterilisation method but have not received a response. We cannot therefore confirm that they are safe to use and recommend that parents/carers who want to use these feeding bottles sterilise them using any of the three sterilisation methods recommended by the NHS (cold-water, steam and boiling), placing all 6 parts of the bottles in the steriliser separately.

Guidelines for parents and carers on making up infant milks safely can be found at:

NHS Bottle feeding Advice

Guide to Bottle Feeding (

The NCT also has a factsheet for parents –

NCT Using infant formula: your questions answered

There are a number of UV sterilising devices on the market, some of which are marketed specifically for use with infant feeding equipment. However, we have not been able to find any evidence which demonstrates that UV sterilisers are effective for use in this way. We have been in communication with the FSA about this and their response was:

‘We have had a look for specific research for UV sterilizers for infant feeding and their safety and effectiveness and we were unable to find any scientific reports about this.

 UV radiation has a germicidal effect and it is used in water treatment as well as in air vents. UV-C is an effective surface disinfectant, however it does not penetrate surfaces and cannot disinfect soiled surfaces. The inability of the UV radiant energy to reach shadowed recesses of surfaces or to penetrate coverings like dust and other matter may negatively affect disinfection.

 There is an FAQ IES Committee Report, where you can find useful information about UV-C, produced in response to the use of UV light to inactivate Covid-19 particles (page 10 section 4.1 answers questions on surface disinfection). FAQ from the IES Committee Report

Given the lack of publicly available evidence that UV sterilisation devices is effective for infant feeding equipment, we would not recommend their use. Instead, we recommend that parents/carers use any three of the sterilisation methods recommended by the NHS, i.e.cold-water, steam and boiling.

Guidelines for parents and carers on making up infant milks safely can be found at:

NHS Bottlefeeding Advice

Guide to Bottle Feeding (

The NCT also has a factsheet for parents –

NCT Using infant formula: your questions answered

Water filters used domestically work in a variety of ways to remove contaminants such as chlorine from drinking water, improve taste and odour and prevent limescale formation.

Whilst there are a variety of different types of water filters on the market including whole house water supply systems and single tap drinking water systems, filter jugs are the most afforable and widely used methods to filter tap water for domestic consumption. Filter jugs rely on filtration media like charcoal and/or ion exchange resins that remove the mineral ions resposible for water hardness and contaminants that affect the taste and odour of water without adding sodium. Whilst theoretically there are no safety concerns around making up infant formula using water from this type of filter jug (where it is regularly cleaned and maintained according to the manufacturers instructions), current advice from the NHS is to use boiled drinking water from the tap to prepare infant formula.

Guidelines for parents and carers on making up infant milks safely can be found at:

NHS Bottlefeeding Advice

Guide to Bottle Feeding (

The NCT also has a factsheet for parents –

NCT Using infant formula: your questions answered

Current NHS guidance for the preparation of powdered infant formula is to boil at least 1 litre of fresh water from the cold tap in a kettle and then leave it to cool for no longer than 30 minutes. Following these instructions, it is expected that the water temperature should be at least 70˚C when the formula powder is added.

The advice to boil the water is important to ensure that potential bacteria in tap water (which is not sterile) is killed. The advice to use the water when it is still more than 70⁰C is to kill any bacteria in the powder (which is also not sterile). Using water at a temperature lower than 70⁰C increases the likelihood that the water temperature may be too low to effectively eradicate any bacteria that may be present in the powder.

Using hotter water, at a temperature of up to 100⁰C is acceptable from the perspective of killing bacteria in the powder, although it may also modify some proteins which may have an impact on how infant formula tastes. Water used at 100⁰C will also kill probiotic bacteria in formula where it is has been added as an ingredient. However, probiotics have no proven benefits for infants when added to infant formula and the priority when reconstituting powdered infant formula should always be optimising microbiological safety rather than maintaining any live bacteria. Care should be taken to avoid scalding when using very hot and boiling water.

Guidelines for parents and carers on making up infant milks safely can be found at:

NHS Bottle feeding Advice

Guide to Bottle Feeding (

The NCT also has a factsheet for parents –

NCT Using infant formula: your questions answered

You can feed a baby both expressed breastmilk and infant formula from a cup from birth using any clean, open cup with a smooth surface. The NHS state that when infants are developmentally ready for complementary feeding at around 6 months old, they should be encouraged to drink from a cup or beaker themselves. They provide some information on how to choose the right kind of cup or beaker for babies and young children to drink from themselves, recommending one with a free-flow lid (without a non-spill valve) over a bottle or beaker with a teat as it helps the baby to learn how to sip rather than suck.

It is not necessary to sterilise open cups and sippy cups but they should be washed in warm soapy water and rinsed and dried following use. Although this may seem at odds with NHS advice on sterilising feeding bottles and equipment for a baby’s first year, the rationale is that feeding bottles and teats have many hard to reach corners and surfaces and sterilisation is the only reliable method of ensuring an appropriate level of cleanliness.

Guidelines for parents and carers on using feeding cups can be found at:

Drinks and cups for babies and young children – NHS (


Ready to feed infant milks are available in 70ml, 90ml, 200ml and 1L bottles or cartons. The Unicef guide to bottlefeeding states that opened RTF infant formula may be stored for up to 24 hours at the top and back of the fridge but currently this recommendation does not differentiate on the basis of pack volume. Manufacturers instructions consistently recommend that for 200ml pack volumes, the opened product may be stored for 24 hours and the 1L pack volume may be stored for 48 hours in the fridge. We recommend  as additional precautionary measures that when using RTF infant fomula, the outside of the manufacturer’s bottles or cartons are cleaned with warm soapy water prior to storing them in the fridge. And where possible, that the fridge temperature should be checked to ensure it is consistently below 5 degrees centigrade. Where the fridge temperature is inconsistent and rises above 5 degrees centigrade it may be a safer option to use powdered infant formula, made up freshly for each feed according to NHS guidance.

RTF infant formula in 70ml or 90ml bottles marketed as starter packs are for one feed only and should not be stored once opened.



Unused bottles of formula should be discarded if they have been kept at room temperature for over 2 hours. This guidance applies to both RTF and formula made-up from powder.

There is no clear guidance around how long infant milk remaining in the bottle may be stored at room temperature after a feed. Where feeds have been started, NHS guidance recommends that any formula leftover in the bottle should be discarded at the end of the feed. Some manufacturers say to dispose of any formula remaining in the bottle immediatley after a feed whilst others say as soon as possible, but at least within 1 hour. Babies may take some time feeding spending time both on and off the bottle and may take as little as a few minutes  or much longer when feeding responsively. It would therefore seem practical and consistent with manufacturers recommendations to recommend that prepared formula milk, which has been used for a feed, whether from RTF, or from PIF should spend no longer than 1 hour at room temperature before being discarded.

Guidelines for parents and carers on making up and storing infant milks safely can be found at:

NHS Bottle feeding Advice

Guide to Bottle Feeding (

There are no formal recommendations on how to transition a baby from infant formula to cows’ milk once they reach 12 months of age. If a child is struggling to accept cows’ milk when directly switched from infant formula, one practical suggestion would be to mix a little cows’ milk with formula to begin with and gradually increase the amount of cows’ milk in subsequent milk feeds until the child is accepting the cows’ milk alone.

If this approach is taken and powdered infant formula is used it is essential that the formula is made up according to the NHS guidelines to mitigate the risk of any bacterial contamination from the water or powdered milk. Any of the prepared milk and infant formula mix that is left over in the cup should be treated as if it were infant formula only and disposed of immediately after use.



Probiotic powders marketed for use from birth have recently been introduced to the UK market by one of the main infant milk manufacturers. The product is regulated as a food supplement and is marketed to improve symptoms of infantile colic. The powders are designed to be mixed with either infant formula or breastmilk.  Probiotic powders are not sterile and therefore adding them to infant formula according to the manufacturers instructions  i.e. adding them to lukewarm infant formula, increases the risk of bacterial contamination. Furthermore there is no robust evidence for any health benefits for healthy term infants from consumption of probiotics.

There has been a large number of studies and reviews conducted on the efficacy of adding probiotics to infant milk for healthy of full term infants but results are inconsistent. Whilst there is some evidence of favourable outcomes, there is a consensus that variations in types of probiotics used and dosage makes it difficult for recommendations to be made. A recent rapid review looking at evidence for a benefit from the addition of probiotics on infantile colic concluded that there was some limited evidence of benefit in full-term breastfed infants (Karkhaneh et al, 2019). However, it has been concluded elsewhere that there is little evidence to show that  supplementing healthy breastfed term infants in the first six months of life with probiotics provides any health benefits (Quin et al, 2018).

In a systematic review of randomised control trials (RCTs) that compared the use of probiotics and/or prebiotics in infant or follow-on formula milks, the ESPGHAN

Committee on Nutrition noted that, whilst there was some evidence available to suggest an association between the use of specific probiotics in formula milk and a reduction in the incidence of gastrointestinal infections and antibiotic use, there was too much uncertainty to draw reliable conclusions. The routine use of probiotic supplements in formula milk for infants was not recommended. The committee did in fact raise some specific concerns about the use of probiotics in infants as follows:

“First, timing, that is, the administration often begins in early infancy, sometimes at birth

when the gut microbiota is not fully established, and factors that influence microbiota may

permanently affect the development of the ecosystem. Second, duration, that is, the daily

administration of such products is often prolonged (several weeks or months). Last but not

least, delivery is in the form of a specific matrix (infant formula) that could be the only source

of feeding of an infant.” (Braegger et al, 2011)

 We would urge caution in the use of probiotics in infant milks and believe that the known risks posed by bacterial contamination should take precedent over the use of probiotics in infant formula where benefits are debated and long term risks are not known. You can find more information about the use of probiotics in infant formula on pages 26-30 of our report: The bacterial contamination of powdered infant formula



Braegger C, Chmielewska A, Decsi T, et al. Supplementation of infant formula with probiotics and/or prebiotics: a systematic review and comment by the ESPGHAN committee on nutrition. Journal of Pediatric Gastroenterology and Nutrition. 2011 Feb;52(2):238-250. DOI: 10.1097/mpg.0b013e3181fb9e80. PMID: 21150647.

 Karkhaneh, M, Fraser L, Jou H, Vohra S (2019). Effectiveness of probiotics in infantile colic: A rapid review. Pediatrics and Child Health, pxz007,

Quin C Estaki M et al (2018) Probiotic supplementation and associated infant gut microbiome and health: a cautionary retrospective clinical comparison. Sci Rep, 8, 8283, accessed at