Quick Answer
Yes, in most cases it is safe to put breast milk back in the fridge after your baby has drank from it, as long as a few guidelines are followed:
- Breast milk should not be left out of the fridge for longer than 4 hours before being put back in.
- Only milk that came into contact with your baby’s mouth should be discarded – unused milk can go back in the fridge.
- Previously frozen milk that was thawed but not fully consumed can be refrigerated for up to 24 hours.
- Refrigerated breast milk is good for up to 4 days from the time it was pumped.
The key is limiting the time breast milk spends at room temperature to prevent bacterial growth. As long as breast milk is properly stored and handled, it is generally safe for baby to consume at multiple feedings.
Storing Unused Breast Milk
If your baby does not finish all the breast milk you provided during a feeding, the unused portion can safely be returned to the refrigerator for use within 4 days, provided it was never brought to room temperature. Here are some guidelines for storing unused breast milk:
- Seal the bottle or storage container properly after your baby is done feeding.
- Immediately store the unused milk in the back of the fridge, where it is coldest.
- Label the milk with the date it was expressed.
- Use the refrigerated milk within 4 days.
As long as unused breast milk was properly stored in the refrigerator and kept chilled, it poses very low risk to your baby if consumed at a later feeding.
Handling Used Breast Milk
Breast milk that came into contact with your baby’s mouth but was not fully consumed may contain small amounts of bacteria from your baby’s saliva. However, it is generally safe to return used breast milk to the refrigerator under the following conditions:
- It has been sitting out at room temperature for no more than 4 hours.
- Only the quantity consumed is discarded – unused milk can go back in the fridge.
- The milk is immediately chilled in the refrigerator.
- It is used within 4 days of being pumped.
Bacteria grow rapidly in breast milk left out at room temperature. Limiting used breast milk’s time at room temperature prevents substantial bacterial growth. Refrigerating used breast milk after feeding slows further bacteria production.
Thawing and Re-Refrigerating Breast Milk
Previously frozen breast milk that has been thawed but not fully consumed by baby can safely be re-refrigerated and used for the next feeding under the following guidelines:
- Thawed milk can be refrigerated for up to 24 hours until the next feeding.
- After 24 hours, any unused thawed milk must be discarded.
- Thawed milk should not be refrozen.
- Mark the time that the thawed milk was first refrigerated.
Thawed breast milk contains some bacteria, but refrigerating it prevents substantial bacterial growth. By limiting refrigerated thawed milk to 24 hours, you reduce the chance of dangerous bacteria accumulation. Thawed milk should never be refrozen, as this further increases infection risk.
Room Temperature Guidelines
The main factor determining the safety of consumed breast milk is the length of time it sits out at room temperature. Here are some general guidelines:
- Store fresh breast milk in the fridge or freezer immediately after pumping.
- Once refrigerated, limit milk’s time at room temperature to 4 hours max.
- Thawed frozen milk should not sit out for more than 2 hours.
- Discard any unused milk left sitting out longer.
Bacteria grow fastest in the “danger zone” between 40°F and 140°F. By limiting room temperature duration, you reduce the chances of dangerous bacteria accumulation in breast milk.
Signs of Spoiled Breast Milk
Occasionally breast milk can spoil before the recommended 4 day refrigerator storage time. Watch for these signs of spoiled breast milk:
- Smell: Spoiled milk will have a rancid or sour odor.
- Color: Milk may change to a yellow, grey, or orange tint.
- Texture: Milk may appear chunky, clumpy, or separated.
- Taste: Spoiled milk will have a bitter, metallic taste.
If your breast milk exhibits any of these signs, it is safest to discard it. Always do a sight and smell check before feeding your baby spoiled milk.
Storing Leftover Breast Milk
To store and reuse leftover breast milk after your baby has started drinking it:
- Discard any milk from the bottle that touched baby’s mouth.
- Cap the bottle and immediately refrigerate.
- Use refrigerated leftover milk within 4 days.
- Discard any leftover milk not consumed after 4 days.
- If milk was previously frozen, use within 24 hours.
By following safe refrigeration and storage practices, leftover breast milk retains its nutritional value and remains safe for your baby to drink at multiple feedings.
Freezing Leftover Milk
Some mothers prefer to freeze excess leftover milk for later use rather than re-refrigerating. Here are some tips:
- Only freeze leftover milk that has been chilled right after feeding.
- Discard any milk that touched baby’s mouth before freezing.
- Store frozen milk towards the back of the freezer where temperature is most consistent.
- Clearly label milk with the date pumped and quantity.
- Use frozen leftover milk within 6 months.
Freezing inhibits bacteria growth in stored breast milk. Clearly labeling milk prevents confusion and ensures older milk is used first.
Cleaning Bottles and Pump Parts
Properly washing any bottles, nipple, or pump parts that contact expressed breast milk helps prevent bacterial contamination:
- Clean all parts that touched milk thoroughly with hot soapy water after each use.
- Consider using a bottle brush to fully clean bottle and nipple interior.
- Air dry all parts fully before re-assembling and storing.
- Periodically sterilize parts by boiling, steaming, or using a UV sterilizer.
Regular cleaning and occasional sterilizing kills lingering bacteria on pump and bottle parts. This prevents contamination of pumped breast milk.
Avoiding Bacterial Growth
You can inhibit bacteria growth when reusing breast milk by:
- Storing milk in the back of the fridge immediately after pumping.
- Limiting milk’s exposure to room temperature.
- Using clean bottles and pump parts for every use.
- Discarding any milk with separation, clumping, odor, or discoloration.
Adhering to time limits, temperature control, and sanitation practices helps keep bacteria levels low in pumped breast milk. Always inspect milk for signs of spoilage before feeding.
Safety Precautions
Take the following precautions when storing breast milk for multiple feedings:
- Wash your hands before handling pumped milk.
- Avoid adding fresh milk to already frozen or refrigerated milk.
- Throw away any milk from a bottle with backwash in it.
- Use smallest bottle size needed for each feeding.
These basic safety steps reduce the chance of contaminating expressed milk. Combining fresh and stored milk can shorten shelf life. Discarding backwash milk prevents sharing excess bacteria.
Risks of Reusing Breast Milk
There are some potential risks associated with reusing breast milk:
- Bacterial contamination if milk is left out too long.
- Viruses can spread if milk containing backwash is reused.
- Medications in milk may accumulate to higher doses.
- Vitamin content may degrade over prolonged storage.
However, practising good refrigeration, storage, and bottle hygiene substantially reduces these risks. Many health organizations still recommend breast milk as the best infant feeding choice, even when reused.
Alternatives to Reusing Milk
If you have concerns about reused breast milk, some alternatives include:
- Feeding smaller volumes of fresh milk per feeding.
- Donating excess milk to a human milk bank.
- Using fresh pumped milk more frequently than refrigerated.
- Supplementing with an occasional bottle of formula.
Reusing breast milk helps reduce milk waste. But for babies with compromised immunity, medical conditions, or special needs, alternatives may be preferable. Talk to your pediatrician if you have any concerns.
Frequently Asked Questions
For how long can breast milk sit out at room temperature?
Breast milk is safe at room temperature for up to 4 hours. Limiting room temperature duration helps prevent substantial bacterial growth.
Does a baby’s saliva change the composition of breast milk?
A baby’s saliva does not significantly alter breast milk left in the bottle. However, it can introduce some bacteria, so milk with backwash should be discarded.
Can I combine refrigerated fresh and used breast milk in one bottle?
It is not recommended to mix fresh breast milk with any quantity that has entered baby’s mouth, even if refrigerated. Always discard milk that has come into contact with baby’s saliva.
How long can refrigerated leftover breast milk be stored?
Refrigerated leftover milk is generally safe for 4 days after being pumped, provided it has been chilled right away after feeding.
Is it safe to freeze and re-freeze leftover milk multiple times?
Previously frozen milk should not be refrozen after thawing. Multiple freeze-thaw cycles can damage milk components and increase bacterial contamination risk.
Summary
In most cases, it is safe to refrigerate or freeze leftover breast milk after baby has drank from the bottle, as long as proper guidelines are followed. Time limits for room temperature duration and refrigerated storage are key to prevent bacterial overgrowth. With safe handling techniques, leftover breast milk retains its nutritional value for multiple feedings. Checking for signs of spoilage and practising good bottle hygiene minimizes risks. Many health agencies endorse reuse with appropriate precautions. Storing small quantities and discarding backwash milk provides extra safety assurance.
