Baby bottle warming: tips for keeping bugs at bay

With the busy lifestyles led by most new parents, providing warm expressed breast milk or infant formula quickly, and often while you’re not at home, can be a bit of a challenge.

There is a range of options for warming your baby’s bottled milk – whether it’s the tried and true sitting the bottle in a container of boiling water, commercial bottle warmers, or microwave ovens (not recommended, particularly for breast milk).

Whichever method you choose, it’s important to do it safely so you don’t burn baby’s mouth or allow the transfer and growth of bugs that cause tummy upsets. Some bugs can make your baby extremely sick. Signs of foodborne illness to watch out for include: vomiting, fever, irritability and crying, not wanting to feed, or frequent dirty, runny nappies. Powdered infant formula is not sterile, so you should take particular care and follow label preparation instructions closely.

Babies who are pre-term, low birth weight, or who have an illness or condition that means their immune system is weaker than normal are most at risk from harmful bacteria. You should talk to your doctor or lead maternity carer about specific feeding advice.

For all babies, but especially those under 3 months of age, it is very important that caregivers are scrupulous about hygiene when making, storing and feeding infant formula or expressed breast milk.

Health professionals, our Ministry of Health and the World Health Organization all agree that babies should be fed breast milk wherever possible. Breast milk contains all the nutrition newborn babies need, and breastfeeding benefits both mother and baby. There are times when bottle feeding with either expressed breast milk or infant formula is necessary. Here are some tips for keeping baby’s feed safe:

• Before you touch any of your baby’s feeding equipment or food always wash your hands properly. This means scrubbing with soap and water then drying thoroughly with a clean towel reserved for hands only. Don’t use a tea towel or baby’s feeding cloth. This is such a basic step, but it’s so important.

• Clean and sterilise feeding, expressing and preparation equipment for every feed, until your baby is at least three months old. A dishwasher will clean, but not sterilise.

• Store infant formula powder in its container, sealed, in a cool dry place. Remember, infant formula is not a sterile product. Take care not to transfer harmful bugs by allowing hands or dirty spoons to dip into the powder.

• It’s best to mix powdered infant formula with cooled, boiled water just before you give it to your baby (once your baby is older than three months you can use town-supply tap water, otherwise keep using boiled water until the baby is 18 months old). Use it straight away and throw out any unused formula that's more than two hours old.

• Made up formula can be stored at room temperature for up to two hours, or in the fridge for four hours. Expressed breast milk can sit at room temperature for up to four hours or in the fridge for 48 hours.

• Never reheat already-warmed or partly-used feeds. While it’s tempting to re-use expensive uneaten formula or precious expressed breast milk, bugs may have been transferred by you, or your baby’s lips or hands and it’s easy to lose track of how long the milk has been left at an unsafe temperature.

• If you’re travelling with bottles of breast milk or made up formula, keep them cold in a chilly bag with ice packs and warm only as needed.

• Expressed breast milk or made up formula can be warmed by placing the bottle in a container of boiling water.

• Electronic baby bottle warmers are safe to use as long as you follow the manufacturer’s instructions. Ideally, choose a warmer that sounds an alarm when the right temperature is reached and then automatically switches off. Remove the bottle from the warmer and feed your baby within two hours.

• Some travel models use the car battery as an energy source to heat the milk. Other products have a re-usable warmer pouch which can be activated by bending a metal disc attached. Both of these products are safe to use as long as the formula is made up by mixing the water and powder together just before warming. Remove the formula from the bottle warmer and finish feeding your baby within two hours. Throw out any unused formula.

• Microwaves are not recommended for warming baby’s milk because they can overheat the milk or heat it unevenly. This can cause nasty burns to the baby’s mouth and throat. If you need to use a microwave stop halfway through and shake the bottle, then after heating shake the bottle again and let it stand for two to three minutes. Breast milk should not be warmed in a microwave as this may destroy some of the milk’s immunological properties.

• Whichever method you choose, always shake the bottle once warmed and check the temperature of the milk by shaking some drops onto the inside of your wrist before giving it to your baby.

The New Zealand Food Safety Authority and Ministry of Health have developed guidelines for warming infant formula. NZFSA also has general advice for feeding your baby safely . For more advice on preparing and using infant formula, ask your lead maternity carer or your Plunket nurse.

Published in Bounty’s e-newsletter, December 2009