Info from www.childrens.com:
Dawn Schindler, RN, BSN, IBCLC, is a lactation consultant at the Level IV Neonatal Intensive Care Unit (NICU) at Children’s Health℠. She answers commonly asked questions about how to store expressed (pumped) breast milk.
Breastmilk Storage Guide: Everything You Need to Know
Reviewed by Dawn Schindler, RN, BSN, IBCLC — Lactation Consultant, Children’s Health℠ Level IV NICU
Storing expressed breast milk doesn’t have to be complicated. Whether you’re a first-time mom or building up a freezer stash, understanding the basics of breastmilk storage will give you confidence and help you avoid wasting a single drop. Below, we answer the most common questions parents have about pumping, storing, and using breast milk safely.
What Is the Best Way to Store Breast Milk?
Breast milk can be stored in any clean, tightly sealed container. Always label every container clearly with the date and time it was pumped. Good options for breastmilk storage include:
- Breast milk storage bags (preferred over regular sandwich bags)
- Glass or plastic bottles with secure caps
“Don’t rely on the bags to measure the volume of your milk accurately,” says Dawn Schindler, RN, BSN, IBCLC, a lactation consultant at the Children’s Health℠ NICU. “Measure it in the bottle first, then write the amount — along with the date and time — on the bag so you know exactly how much is in each one.”
If your baby is in a NICU or hospital setting, ask about specific labeling requirements. These often include:
- Baby’s full name and date of birth
- Mother’s name and date of birth
- Time and date the milk was pumped
- Any prescription or over-the-counter medications the mother is taking
How Long Does Breast Milk Last?
At Room Temperature
How long does breast milk last at room temperature? Freshly pumped breast milk can safely sit out at room temperature for about four hours. After that, it should either be fed to the baby or moved to the refrigerator or freezer. Jot down the time you pumped and keep it somewhere visible so you don’t lose track.
In the Refrigerator or Freezer
The Centers for Disease Control and Prevention (CDC) recommends:
- Refrigerator: Up to 4 days (store toward the back where it’s coldest)
- Deep freezer: 6–12 months
To stay organized, keep the oldest milk at the front so it gets used first. In the freezer, group all your breast milk together so it’s easy to find.
One smart tip from Schindler: freeze milk in the volume your baby drinks at each feeding. “Don’t put 8 ounces in a bag if your baby is only drinking 4 ounces at a time,” she explains. “This helps you thaw the right amount and avoid wasting milk.”
Can You Mix Breast Milk from Different Days?
Yes — mixing milk from different pumping sessions is completely safe. Schindler recommends combining cold milk with cold milk. Store your pumped sessions separately in the fridge, and once everything has cooled to the same temperature, you can combine them into one bottle or bag.
When you do mix, label the combined milk with the date and time of the first pumping session — that’s what determines when it expires.
Can Warmed Breast Milk Be Refrigerated Again?
According to the CDC, breast milk that has been offered during a feeding can be saved for up to two hours afterward. After that window, it should be discarded. Bacteria from the nipple of the bottle can contaminate the remaining milk, so it’s not safe to keep it longer than two hours.
How Do I Safely Defrost Frozen Breast Milk?
Start by moving frozen milk to the refrigerator or freezer transfer — placing it in the fridge to thaw slowly and safely. Once there are no ice crystals remaining, the milk is fully thawed and can be kept in the refrigerator for up to 24 hours.
If you’re short on time, you can place the bag or bottle in a bowl of lukewarm water to speed up thawing. Once it’s fully liquid, warm the amount your baby needs for that feeding. Any remaining milk can go back in the fridge for up to 24 hours.
Important: Once breast milk has been thawed, never refreeze it.
What If My Breast Milk Smells Funny After Defrosting?
The food you eat and natural enzymes in your body can change the smell of breast milk — this is normal. “Most of the time, babies don’t notice a small change in taste or smell,” Schindler says. “If your baby refuses defrosted milk, try mixing it with freshly expressed milk.”
One thing to know: the enzyme lipase breaks down the fat in breast milk, which can cause a soapy or sour smell after freezing. This is harmless, but some babies don’t like the taste. If the smell continues, even in fresh milk, talk to your baby’s pediatrician or a lactation consultant.
Does Breast Milk Need to Be Warmed Before Feeding?
Not necessarily. Newborns tend to prefer warm milk, but older babies often accept cooler or room-temperature milk just fine. If your baby prefers it warm, heat the milk in a cup or bowl of warm water. Never use a microwave — it heats unevenly and can create hot spots that may burn your baby’s mouth.
How Do I Transport Breast Milk Safely?
Whether you’re heading to daycare, a family member’s home, or the NICU, follow these simple steps:
- Place all expressed milk in an insulated cooler packed tightly with ice packs.
- Resist the urge to open the cooler to check on it — temperature stability matters.
- Breast milk stays safe in a cooler with ice packs for up to 24 hours.
Final Thoughts on Breastmilk Storage
Breastmilk storage can feel like a lot to remember at first, but once the routine clicks, it becomes second nature. The key rules are: label everything, keep track of time, freeze in feeding-size portions, and never refreeze thawed milk.
If you have questions or run into challenges, don’t hesitate to reach out to a lactation consultant or your baby’s pediatrician — they’re there to help.
Sources: Centers for Disease Control and Prevention (CDC); Dawn Schindler, RN, BSN, IBCLC, Children’s Health℠
