Infant formula is a medical marvel. It is safe and nutritious for babies who are unable to drink breastmilk (also known as human milk). Some infant formulas come as powders that are mixed with water for the baby to drink. So, is powdered infant formula sterile?
Some parents are surprised to find that the powdered formulas are actually not sterile. Because they can potentially carry harmful bacteria that can make a baby sick, care needs to be taken when preparing the formula.
Many families boil water when preparing infant formula. This helps kill harmful bacteria that can be present in the formula powder itself.
Today’s post reviews some basic information about infant formulas. It also includes why some experts may recommend that water be boiled when preparing the formula. This is especially important for babies under age 3 months, premature infants, or those with otherwise vulnerable immune systems.
I also have a quick note at the end about why homemade infant formula is not a safe option.
When is powdered infant formula needed?
Both the World Health Organization (WHO) and the American Academy of Pediatrics (AAP) recommend babies drink only breast milk for the first six months of life. If this is not possible, then infant formulas are an alternative.
For their entire first year of life, babies need to drink either breastmilk or infant formula. They’re too young for pure cow’s milk or other plant-based milk products. Breast milk is the ideal nutrition, so many formulas strive to have similar nutritional value.
Infant formula at the store is sold in a few different forms. A common type of formula is a powdered formula. In this case, a caregiver adds water and mixes it before feeding their baby.
Another option is called “ready to feed.” This is a premade liquid formula. Nothing needs to be added or mixed into the baby bottles prior to feeding the infant. (A liquid concentrate is also available, but less common, in my experience).
The ready to feed formula is considered sterile. As a sterile product, this means there are no germs or bacteria in the container before it is opened.
However, powdered infant formula is not sterile. As it is being processed, there are many steps where bacteria can enter. (As it is made from several ingredients, any one of them could contaminate the formula itself). It can also happen during processing and packaging.
This is rare! Most infant formula is not contaminated. However, it is possible, and this is why safe preparation of powdered formula may include a few extra steps.
May 2022 update: This article in the New York Times describes more detail about one of the manufacturers of infant formulas and the many possible opportunities for bacteria to grow. Here, federal investigators did find unsanitary conditions that could lead to bacterial contamination.
Since powdered infant formula is not sterile, there are a few steps to take.
I consider these steps extra important for:
- newborn infants and those younger than 3 months of age
- babies born prematurely
- babies who have another medical reason to be extra vulnerable
These babies are more susceptible to infection. A baby’s pediatrician will let the family know if their child is considered more vulnerable. They can tell you if extra precautions are needed. In these situations and at these young ages, choosing the sterile liquid infant formula (the “ready to feed” formula) is very reasonable!
If powdered formula is needed, there are a few extra steps.
The WHO recommends boiling water before adding the powdered formula. They advise bringing the water to a rolling boil. While the water is still hotter than 70°C (158°F) pour it into the baby’s bottle. Then add the formula powder. This hot water will kill many bacteria and viruses if they’re present in the powder itself.
Standard recommendations for preparing questionable water for drinking include having the water at a rolling boil for an entire minute before using. (At elevations above 6500 feet, this needs to be three minutes). This will make the water itself safer. It still needs to be more than 70°C before adding to the powder. Usually, it takes less than 30 minutes for it to cool below 70°C.
The detailed instructions for formula preparation from the WHO are here. See a summarized approach below. Please discuss your specific situation with your child’s health care professional. They can help you come up with the safest way to prepare your baby’s formula.
Summary of Steps for Powdered Infant Formula Preparation
- Boil water.
- Add the boiled water to a clean bottle before it has cooled below 70°C (158°F). The product label on the formula container will tell you how much water to add for the amount of formula you want to make.
- Add the correct amount of powdered formula to the bottle. (See formula can label for directions and the manufacturer’s instructions on amount. Be sure to check the expiration date).
- Close the bottle with a clean lid and nipple.
- Shake the bottle to mix.
- Wait for the bottle to cool. It may be placed in a cup of ice water or cold tap water to speed up the process. Just be sure that the (nonsterile) cold water does not touch the nipple or parts of the bottle that the baby may have in their mouth.
- Check the temperature of the formula. Some families put a few drops onto the inside of their wrist.
- Feed the baby.
Ensure hands, surfaces, and supplies are clean.
All of the above steps need to be done with clean hands. Hands need to be washed well. The surface upon which the bottles are prepared needs to be cleaned thoroughly. And, the bottles, lids, and nipples all need to be cleaned. This means that an empty bottle from a previous feed cannot be reused until it has been washed.
Use a glass bottle if possible.
Ideally, the bottle should be made of glass. Hot water added to plastic is not recommended due to possible toxins in the plastic. This isn’t always possible, of course. And, I don’t want to scare anyone who has used plastic bottles. But I do think it’s better to share this information so that you’re empowered to choose what’s best for your family. Convenience matters too.
If boiling water is not possible:
If boiling water is not possible, clean water from a reliable source is another option. Many use bottled water (or contact their health department if tap water is unreliable). In the U.S., the Centers for Disease Control advises following the manufacturer’s instructions on a can of formula, indicating boiling is not always necessary for older and less vulnerable babies. The prepared bottle should be consumed right away and not stored (see below).
Can powdered infant formula be prepared in advance?
With all those steps, it may be tempting to prepare a large batch of formula at once. Or, if a baby takes only a few sips then refuses the rest of the bottle, it’s tempting to just keep the bottle ready until the baby feeds again. It’s hard to throw out an entire bottle of formula just because a baby didn’t finish eating it.
However, it’s best to prepare each feed as the baby needs it. Because powdered infant formula is not sterile, bacteria can grow if left out for too long. So, using leftover formula is not a good idea. As mentioned, some bacteria can make babies very sick or even cause fatal infections.
Serving and Storage of Infant Formula
A bottle of prepared infant formula can be stored in a refrigerator for up to 24 hours. After that, bacteria are more likely to grow.
It’s okay to serve it cold, but some babies prefer warm formula. The bottle can be placed in warm water to heat. (Do not use a microwave oven to reheat the formula. Because of uneven heating, there can be surprising “hot spots” in the bottle that can burn a baby’s mouth).
Once a baby has started a feed, the formula should be finished within an hour. Otherwise the bacteria from the baby’s mouth combined with the formula can cause the formula to spoil.
If a prepared room temperature feed has not been started within two hours, it should be thrown away. Again, this is because bacteria may start to grow in prepared formula at room temperature.
Prepared formula should not be frozen and then thawed/rewarmed later. As a reminder, it’s safest to prepare each feed as needed.
Are all these steps practical?
All of the above are official recommendations in an ideal setting. I know it’s a lot and not always easy. My goal here is to share that ideal so that you can make the best choices for your baby. Especially for babies over age 3 months, families can discuss formula preparation options with their physician. For example, they can decide together if using clean tap water is sufficiently safe.
Thoughts on Homemade Infant Formulas
A quick Google or Pinterest search reveals the popularity of homemade infant formulas. Some parents have developed their own recipes. They describe ingredients that they feel align with their family’s values. However, I need to be very clear here. Homemade infant formula is not safe. Contamination is a very real risk. Nutrition may be inadequate as well. And, because a baby’s entire diet may be formula, this is incredibly significant. Growth, weight gain, brain development, and overall health are dependent on the formula. Store bought formulas are highly regulated. They’re also extensively studied to optimize nutrition for young infants.
Homemade formulas, even “custom homemade formulas” are not regulated and should not be used.
If a family worries about specific ingredients in store bought formula, I suggest they chat with their pediatrician. There are many varieties of formula for many different dietary preferences. Most families can find one that suits them.
Perfect does not need to be the enemy of “okay.”
I think guidelines can feel overwhelming for some families. Parents may feel like ignoring all guidelines just because a few are too difficult. It does not need to be this way. There are many safe and healthy ways to feed our babies. For example, just because breastmilk is “ideal,” it doesn’t mean formula is bad. Just because we should avoid plastic bottles doesn’t mean you shouldn’t feed your baby if plastic is all that’s available. Infant feeding isn’t black and white.
This applies to many things in parenting and children’s health. Again, I share here so that families are empowered with complete information in order to make informed decisions.
Maya Mahmood, D.O., FAAP is a board-certified pediatrician and mom. She is passionate about parents having evidence-based information to help their families be healthier.
Content on this site and from MayaPeds LLC is for information only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding your baby’s health. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
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