Especially for premature, low-birth-weight and under-2-month-old infants: Use water at least 70 °C to prepare formula, then let it cool before feeding; discard any leftovers

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.

Powdered formula is not sterile. It can carry Cronobacter sakazakii. The reported death rate after a newborn is infected is 40% to 80%. Experimental work shows: pour the hot water into the bottle first, wait until the water falls to about 73.8 °C, then add the powder, and in the great majority of cases the milk is still above 70 °C. That can cut this bacterium by 5 or more orders of magnitude, down to below 1/100000 of what it was. The price of hot water shows up in vitamin C. The World Health Organization and the UN Food and Agriculture Organization held an expert meeting in 2006. The figures seen at that meeting were: when formula is mixed with boiling water, only vitamin C falls clearly, by 5.6% to 65.6% across 4 formulas. Formula leaves the factory with extra vitamin C already added. The formula that lost the most still had 9.0 milligrams per 100 kilocalories after mixing, above the Codex Alimentarius floor of 8 milligrams. The meeting saw only this 1 study, so it drew no conclusion on it. Who is at highest risk? Silano and colleagues report that infants aged 2 months or younger are most susceptible to meningitis after infection; premature and immunocompromised infants also have higher risk. They advocate preparing formula with 70 °C water, especially for premature and low-birth-weight infants.

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；Bundesinstitut für Risikobewertung (2022). Recommendations for the hygienic preparation of powdered infant formula. Updated BfR Opinion No. 009/2022. https://doi.org/10.17590/20220510-104706；Agostoni C, Axelsson I, Goulet O, et al. (2004). Preparation and handling of powdered infant formula: a commentary by the ESPGHAN Committee on Nutrition. Journal of Pediatric Gastroenterology and Nutrition, 39(4), 320-322. https://doi.org/10.1097/00005176-200410000-00002；Silano M, Paganin P, Davanzo R (2016). Time for the 70 °C water precautionary option in the home dilution of powdered infant formula. Italian Journal of Pediatrics, 42, 17. https://doi.org/10.1186/s13052-016-0228-9；Losio MN, Pavoni E, Finazzi G, et al. (2018). Preparation of Powdered Infant Formula: Could Product's Safety Be Improved? Journal of Pediatric Gastroenterology and Nutrition, 67(4), 543-546. https://doi.org/10.1097/MPG.0000000000002100

There is disagreement. Germany’s Federal Institute for Risk Assessment (BfR) advised in 2022 that water at 20–50 °C is suitable for healthy, full-term infants; it noted that most manufacturers recommend 40–50 °C. Its reasoning is that water starting at 70 °C cools quickly in the bottle, so actual bacterial killing may fall short of estimates. Hot water may also reduce nutrients, and feeding without cooling risks scalding. The ESPGHAN Committee on Nutrition also opposed boiling water in 2004 over possible damage to vitamins and added probiotics. WHO and FAO still recommend water at least 70 °C. Premature infants, those with a birth weight below 2,500 g, those younger than 2 months and immunocompromised infants are at highest risk; use the 70 °C approach or ask a doctor. For healthy, full-term infants prepared according to the temperature on the tin, the German opinion considers infection risk extremely low. The 70 °C threshold comes from public-health guidance. Beary and colleagues describe guidance for caregivers of high-risk infants recommending water heated to at least 70 °C (158 °F) to inactivate microorganisms. Do not use water left in a thermos all day, or leave prepared formula at room temperature for the next feed.