Can You Reuse an Unfinished Bottle of Breast Milk?

When you're breastfeeding, you know how valuable your pumped milk is. It takes a lot of time and effort to pump the milk, clean your pump, and package the milk for storage—and that's before even preparing a bottle and feeding your baby! So, it's no wonder parents hesitate to throw out leftover breast milk when their baby doesn't finish the bottle.

At the same time, no one wants to reuse leftover breast milk if it isn't safe. But what exactly are the rules when it comes to those times your baby didn't finish their bottle of breast milk? Can you reuse it later? And if so, how much later?

Read on to learn the concerns about leftover breast milk and whether it's safe to reuse a leftover bottle.

The Risks of a Leftover Bottle of Breast Milk

The main risk with a leftover bottle of breast milk is bacterial contamination. When your baby feeds from a bottle, bacteria from their mouth can get into the bottle and continue to grow and multiply. If you reuse the milk from the bottle later, you risk introducing significantly more bacteria to your baby. The longer the used bottle sits, the more the bacteria grow.

Compounding this issue is that contamination can occur at any time in the process, even before you feed your baby. In fact, bacteria are commonly introduced into expressed breast milk as a result of improper hygiene and milk storage.

According to the Centers for Disease Control and Prevention (CDC), you can reduce the risk of breast milk contamination before feeding your baby by doing the following:

• Washing your hands well before pumping or handling breast milk
• Keeping your pump kit and tubing clean
• Using breast milk storage bags or food-grade containers for expressed breast milk
• Following breast milk storage guidelines

While these steps can help avoid contamination before feeding, bacteria can still be introduced during feeding. What then?

Recommendations for Leftover Breast Milk

Most lactation consultants encourage people to use common sense here. Think about the sandwich you had for lunch. If you only ate half, you might refrigerate it and have the rest for dinner, but you probably wouldn't want to eat it for lunch the next day.

The same goes for breast milk. If, after feeding your baby, you're left with half or a quarter of a bottle, you can reuse it, but only if you're going to do so quite soon.

The CDC advises reusing leftover breast milk within two hours of the last feeding. If it's longer than two hours, you should throw it away. Do not freeze and reuse later.

What to Do If Your Baby Routinely Doesn’t Finish Their Bottle of Breast Milk

It can be frustrating to pour hard-pumped breast milk down the drain. But in this case, it may be best for your baby's health.

If your infant consistently leaves milk behind, put a little less in their bottle at the start of each feeding (you can always offer seconds if they want more). This will prevent unnecessary waste and help you conserve uncontaminated milk for later feedings.

To avoid wasting breast milk or discarding unused milk, the Academy of Breastfeeding Medicine (ABM) advises that people store their milk in different amounts. For example, 4 ounces, 2 ounces, and 1 ounce. That way, if your baby finishes their bottle and is still hungry, you can then offer a smaller bottle. If they don't finish the smaller one, there is much less waste.