Use water hotter than 70 °C to prepare formula, then let it cool before feeding; discard any leftovers.

5. Use water hotter than 70 °C to prepare formula, then let it cool before feeding; discard any leftovers.

Cost: No monetary cost. It only requires a few extra minutes of waiting for the milk to cool. The difficulty lies in the fact that even when a baby is crying from hunger, caregivers must still wait for the water temperature to drop before mixing the formula.

In plain terms: Formula milk is not sterile and may contain a bacterium called Cronobacter sakazakii. Once newborns are infected, reported mortality rates range from 40% to 80%. To minimize this risk, first pour hot water into the feeding bottle, then wait until the temperature drops to around 73.8 °C before adding the formula. At this point, the milk remains above 70 °C, which can reduce the amount of this bacterium to less than one ten-thousandth of its original level. After preparation, let the milk cool completely before feeding, and discard any portions that are not consumed.

Benefit: Formula milk is not sterile and may harbor Cronobacter sakazakii. Reported mortality rates among newborns infected with this bacterium fall between 40% and 80%. Experimental studies show that when hot water is first added to the bottle and the temperature is allowed to drop to roughly 73.8 °C prior to adding formula, the milk temperature stays above 70 °C in most cases. This process reduces the concentration of Cronobacter sakazakii by more than 5 logarithmic units, effectively bringing it down to under one ten-thousandth of its original amount.

Evidence grade: A

Sources: 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>

Notes: The 70 °C threshold is specified in public health guidelines. Beary et al. explicitly state: “Public health guidelines for caregivers of high-risk infants recommend using water heated to at least 70 °C (158 °F) to prepare infant formula, in order to inactivate harmful microorganisms.” Premature infants, those with low birth weight, and babies under 2 months of age are at the highest risk of infection. Never use water that has been stored in a thermos for a full day to prepare formula, and do not leave prepared milk at room temperature for later use.