Because formula is more prone to bacterial growth than breast milk, bottles need to be sterilized every time for the first four months. Wash your hands with hot soapy water, then clean all parts using a bottlebrush.
To sterilize, submerge nipples and bottles in boiling water for two minutes. Place sterilized bottles and formula mixing tools on a piece of paper towel to air-dry instead of a dishtowel, which could contain traces of bacteria. Microwavable steam sterilization bags, or an electrical sterilizer, are also convenient options. Water used to prepare formula should also be boiled for two minutes. (If your baby is older than six months, speak with your doctor about whether you can use hot tap water instead).
Have more bottle-feeding questions? Download our chart here and put it on the fridge—it has the answer to all your questions.