Prepare powdered formula with sufficiently hot water, cool before feeding and discard leftovers
Powdered formula is not sterile and can contain Cronobacter. Reported fatality among infected newborns is 40%–80%. In the cited laboratory study, adding powder when hot water in the bottle had cooled to about 73.8°C usually left the mixture above 70°C and reduced the organism by more than 100,000-fold. Cool to feeding temperature afterward and discard unfinished milk.
What it takes
No extra cost, but allow cooling time. Follow temperature precautions even when the baby is crying with hunger.
What you may gain
Powder can contain Cronobacter sakazakii, with reported neonatal infection fatality of 40%–80%. A laboratory study found that pouring hot water first and adding powder at about 73.8°C kept the mixture at least 70°C in most conditions, producing a reduction greater than 5 log units, over 100,000-fold.
Context & considerations
The 70°C (158°F) threshold comes from public-health guidance, particularly guidance for high-risk infants described by Beary and colleagues. Premature, low-birthweight and under-2-month infants are at highest risk. Do not use water kept all day in a flask or leave prepared formula at room temperature for the next feed.
Research & references
Beary MA, Daly SE, Baker J, Snyder AB (2025). Assessing Hot Water Reconstitution Instructions and Labeling of Powdered Infant Formula to Ensure Cronobacter spp. Reduction. Journal of Food Protection, 88(9), 100571. https://doi.org/10.1016/j.jfp.2025.100571; Sima WG, Legesse T, Girma S, et al. (2025). Emerging microbial risks: Cronobacter sakazakii in powdered infant formula for infants under six months of age in Ethiopia. BMC Microbiology, 26, 307. https://doi.org/10.1186/s12866-025-04380-y; World Health Organization & FAO (2007). Safe preparation, storage and handling of powdered infant formula: guidelines. https://www.who.int/publications/i/item/9789241595414