How to Prepare Formula Safely: A Step-by-Step Guide

Key takeaways: Follow the label exactly, every time. Never dilute or concentrate formula. For babies under 2 months, preterm, or with weakened immune systems, take extra precautions with powdered formula or use ready-to-feed. Use prepared formula within 2 hours, and within 1 hour once your baby starts drinking.

Infant formula is carefully designed to give babies the right balance of nutrients. Preparing it correctly is just as important as choosing it. Small mistakes, like an extra scoop or too much water, can make babies sick. Here’s how to do it safely.

Types of Formula

• Powdered: the least expensive. Mixed with water. Powdered formula isn’t sterile, which matters for very young or vulnerable babies.
• Liquid concentrate: mixed with an equal amount of water (always check the label).
• Ready-to-feed: no mixing needed. Sterile until opened and the safest choice for newborns, premature babies, and babies with weakened immune systems, though it costs more.

All infant formulas sold in the U.S. must meet FDA nutrient requirements. Store brands meet the same standards as name brands.

Step-by-Step: Powdered Formula

1. Wash your hands with soap and water. Clean the counter where you’ll prepare the bottle.
2. Check the formula. Look at the expiration date and make sure the container isn’t dented, bulging, or damaged.
3. Use safe water. Tap water from a safe public supply or bottled water both work. If you use well water, have it tested, and boil it before use.
4. Add the water to the bottle first. Measure the exact amount the label says.
5. Add the formula powder. Use only the scoop that came with that container. Fill it loosely and level it off with a clean, dry knife or the leveler built into the container. Don’t pack it down.
6. Close the bottle and shake well.
7. Check the temperature. Babies can drink formula at room temperature, warm, or cool. If you warm it, set the bottle in a bowl of warm water. Never microwave formula; it heats unevenly and can create hot spots that burn your baby’s mouth. Test a few drops on the inside of your wrist; it should feel lukewarm, not hot.

Extra Precautions for Young and Vulnerable Babies

Powdered formula isn’t sterile and can rarely contain germs, including Cronobacter, which can cause serious infections in young babies. For babies under 2 months old, born prematurely, OR with weakened immune systems, the CDC suggests extra precautions:

• Use ready-to-feed or liquid concentrate formula when possible, or
• Prepare powdered formula with hot water: bring safe water to a rolling boil, let it cool for no more than 5 minutes so it’s still at least 158°F (70°C), add the powder, and mix. Then cool the bottle quickly under cold running water or in an ice bath, and test the temperature before feeding.

Liquid Concentrate

Shake the can, then mix equal parts concentrate and water unless the label says otherwise. Refrigerate an opened can, covered, and use within the time on the label (usually 48 hours).

Ready-to-Feed

Shake the container and pour into a clean bottle, or attach a nipple directly if it’s a single-serve bottle. Don’t add water. Refrigerate opened containers and use within the time on the label.

Never Dilute or Concentrate Formula

• Too much water can cause dangerously low sodium levels (water intoxication), leading to seizures, and can lead to poor growth.
• Too little water (too much powder) can cause dehydration and strain your baby’s kidneys.

If you’re struggling to afford formula, don’t stretch it with water. Talk to your baby’s doctor, contact your local WIC office, or ask about community resources and food banks.

Never make homemade formula, and don’t give babies under 12 months cow’s milk, goat’s milk, plant-based milks, or toddler formulas instead of infant formula.

Storage and Timing

• Use prepared formula within 2 hours if left at room temperature.
• Once your baby starts drinking, use within 1 hour, then throw away what’s left. Saliva introduces bacteria.
• Prepared bottles you won’t use right away go in the refrigerator immediately and should be used within 24 hours.
• Opened containers of powder: close tightly, store in a cool, dry place (not the refrigerator), and use within the time on the label, usually about 1 month.

Night Feeds and Outings

• Keep pre-measured powder in a clean, dry container and a separate bottle of water; mix right before feeding.
• Or use ready-to-feed formula for convenience.
• Use an insulated bag with ice packs for refrigerated bottles.

Formula Recalls

Check the FDA’s recall list occasionally, or sign up for alerts. If your formula is recalled, call your baby’s doctor for advice on a substitute.

Call your baby’s doctor if your baby: has fever, vomiting, diarrhea, poor feeding, unusual sleepiness, or fewer wet diapers, especially if you think the formula may have been prepared incorrectly or was recalled. Call 911 if your baby has a seizure.

The Bottom Line

Wash your hands, follow the label exactly, and never water down formula. Take extra care with powdered formula for young or vulnerable babies, and toss leftovers on time.

For more on newborn health and when to call the doctor, see my book From First Breath to First Birthday.

Sources

1. Centers for Disease Control and Prevention. How to prepare and store powdered infant formula. https://www.cdc.gov/infant-toddler-nutrition
2. Centers for Disease Control and Prevention. About Cronobacter infection. https://www.cdc.gov/cronobacter
3. World Health Organization. Safe Preparation, Storage and Handling of Powdered Infant Formula: Guidelines. Geneva: WHO; 2007.
4. US Food and Drug Administration. Questions & answers for consumers concerning infant formula. https://www.fda.gov
5. Abrams SA, Daniels SR. Protecting vulnerable infants by ensuring safe infant formula use. J Pediatr. 2022;249:10-13.
6. American Academy of Pediatrics. How to safely prepare formula with water. HealthyChildren.org. https://www.healthychildren.org

This article is for general education and is not a substitute for individualized medical advice. Always talk with your baby’s health care provider or your own provider about your specific situation. If you think your baby or you may have a medical emergency, call 911.