How Long Can Breast Milk Sit Out? What About in the Fridge? All of Your Questions Answered

For many moms, breast milk is like liquid gold—a single drop can be too valuable to waste. So knowing how to properly store, refrigerate and freeze your breast milk is priceless info when you’re breastfeeding. And what if you leave breast milk sitting out? When should you toss it? Here’s the lowdown so you (and your baby) won’t be crying over spoiled breast milk.

“If it will be used within four days, breast milk should be stored in the refrigerator,” explains Lisa Paladino, certified lactation consultant and midwife. “If it won’t be used within four days, it can be frozen for six to 12 months, but it’s best used within six months.” Julie Cunningham, registered dietitian and certified lactation consultant, offers slightly modified guidelines, suggesting parents follow the “Rule of Fives” when storing breast milk: “It can stay at room temperature for five hours, stay in the refrigerator for five days, or stay in the freezer for five months.”

Ideally, breast milk should be used or refrigerated immediately after it’s expressed, but according to the Centers for Disease Control and Prevention, it can sit at room temperature (77°F) for up to four hours. When storing it in the fridge or freezer, Paladino warns against combining breast milk of different temperatures in the same container. “For example, freshly pumped milk shouldn’t be poured into a bottle in the refrigerator that is already cold or a bottle in the freezer that is already frozen,” she says. Instead, cool down the newly expressed milk before adding it to a half-full container. Also, don’t combine breast milk that was expressed on different days.

When it comes to containers, use covered glass or hard plastic ones that are free of BPA or storage bags specially designed for breast milk (don’t use basic sandwich bags). Keep in mind, though, that the bags could tear or leak, so it’s best to place them in a hard plastic container with a sealed lid when storing in the fridge or freezer.

Paladino also suggests trying silicone molds that are similar to ice cube trays, which “are designed to freeze breast milk in small quantities that can be popped out and individually defrosted. These are eco-friendly and convenient.” Storing breast milk in small amounts is a good idea if you have a young baby, Cunningham adds, since “it's no fun to see your milk go down the drain when the baby doesn't drink it all.”

To help cut down on wasted breast milk, fill up each storage container with the amount your baby will need for one feeding, starting with two to four ounces, then adjust as needed.

Label each container with the date you expressed the breast milk, and if you're planning to store the milk at a daycare facility, add your baby's name to the label to avoid confusion. Store it in the back of the fridge or freezer, away from the door, where it’s coldest.

To thaw out frozen milk, place the container in the fridge the night before you’ll need it or gently warm the milk by placing it under warm running water or in a bowl of warm water. Do not defrost the breast milk at room temperature.

Once it’s thawed properly, it can be left at room temperature for one to two hours, according to the CDC. If it’s sitting in the fridge, be sure to use within 24 hours, and don’t refreeze it.

Also never defrost or heat up breast milk in a microwave, Paladino says. Cunningham adds that, as with infant formula, breast milk should never be microwaved since it can scald a baby's mouth, “but also because microwaving kills the live antibodies in the breast milk that are so good for the baby.”

Because of this, fresh is always best, according to Cunningham. If available, freshly pumped milk should be given to a baby before refrigerated or frozen milk. “A mom makes antibodies to germs that a baby gets exposed to in real time, so breast milk is best for fighting germs when fresh.”

Plus, your breast milk’s properties develop and change as your baby grows; the milk you expressed when your baby was eight months old is not the same as when your baby was four months old. So keep that in mind when freezing and thawing your breast milk.

Breast milk can sit out at room temperature for up to four hours before you need to toss it, Paladino says, while some sources say up to six hours. But this also depends on the temperature of the room. The higher the temp, the faster bacteria can grow. To be safe, aim to use room temperature breast milk within four hours. Discard any leftover milk from a used bottle after two hours, the CDC advises. That’s because the milk may have potential contamination from your baby’s mouth.

“In general, I instruct parents to use guidelines for breast milk that they would use for any other liquid food, for example, soup,” Paladino says. “After cooking soup, you wouldn’t leave it out for more than four hours at room temperature and you wouldn’t keep it in the freezer for more than six to 12 months.” 

These breast milk storage guidelines apply to full-term babies with healthy immune systems. Check with your doctor if your baby has any health complications or is premature, and may be at a higher risk of infection.