The pharmacy-trained guide to safe formula preparation, the too-concentrated formula risk, follow-on formula myths, and how to read a baby food label — everything the brands do not put on the front of the pack.
Formula preparation is one area where parents are often given contradictory advice — some say make it in advance, some say use the microwave, some say cooled boiled water is fine. The NHS and WHO are unambiguous on this. Here is exactly how to prepare formula safely.
The reason formula must be made with water at 70°C or above is to kill Cronobacter sakazakii — a bacteria found in powdered formula that can cause meningitis and sepsis in newborns. Cooled boiled water does not kill it. Pre-made bottles stored in the fridge and reheated do not maintain the sterility needed at the point of preparation.
The correct method: boil fresh water. Allow it to cool for no more than 30 minutes — it should still be at least 70°C. Add the correct number of scoops (level, not heaped) to the water — not water to powder. Cool rapidly under running cold water or in a bowl of cold water until comfortable temperature. Feed immediately.
All feeding equipment must be sterilised until your baby is 12 months old. This includes bottles, teats, caps, and rings. Three safe methods: electric steam steriliser, microwave steam bag, cold water sterilising solution.
Wash all equipment in hot soapy water before sterilising. Dishwashers clean but do not sterilise — dishwasher-clean bottles still need sterilising.
Breast milk does not require sterilisation — it contains antibodies that inhibit bacterial growth. Expressed breast milk can be stored in the fridge for up to 5 days at 4°C or lower, or frozen for up to 6 months.
Never refreeze thawed breast milk. Do not warm breast milk in a microwave. Defrost in the fridge overnight or by placing the container in warm water.
The NHS recommends introducing an open cup or free-flow cup from around 6 months — alongside weaning. Sippy cups with valves are not recommended as they require the same sucking action as a bottle and do not help the development of mature drinking. Open cups and free-flow cups are better for dental development.
NHS Formula milk · WHO Infant and young child feeding · PHE Safe formula preparation · Reviewed April 2026.