How Long Can Breast Milk Sit Out? Tips For Safe Storage

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Breastfeeding holds great health benefits for both the baby and the mother. Hence, most mothers use expressed breast milk as an alternative to feeding directly from the breast. But how long can breast milk sit out?

The benefits of breast milk greatly depend on the milk’s storage, handling, and expression. Breast milk can serve its purpose the best only if these attributes are managed correctly.

Read on to know how long breast milk can sit out and tips for safe storage of breast milk.

How Long Can Breast Milk Stay Outside?

Breast milk is a perishable food. Whether hand expressed or pumped, it needs to be stored properly. Freshly expressed breast milk stored in glass bottles, BPA-free containers, or specialized breast milk storage bags with tight-fitting lids/caps can stay outside for up to (1) (2):

  • Four hours at a room temperature of 77°F (25°C). However, one can store very cleanly expressed and stored breast milk for six to eight hours.
  • Four days when refrigerated at 40°F (4°C). The time frame can go up to eight days for very cleanly expressed breast milk.
  • Nine months when frozen at 0°F (−18°C) in a freezer with a separate door.
  • 12 months when frozen at -4°F (−20°C) in a deep freezer.

Thawed frozen milk can stay at room temperature (77°F or 25°C) for one to two hours. If you need to refrigerate thawed milk, use it within 24 hours. Don’t refreeze thawed breast milk. Consult a pediatrician to know the proper guidelines for breast milk storage for babies with specialized needs, such as babies with health conditions or those born prematurely.

What Happens If You Leave Breast Milk Outside For Long?

Proper breast milk storage helps maintain its nutritional, immunological, and antioxidant properties (3). Additionally, it helps sustain breast milk’s antibacterial properties. Any deviations from the recommended storage temperature and time can change these properties.

Incorrectly stored breast milk may also be harmful to the baby’s health. The risk escalates multi-folds for babies born prematurely or those with a weak immune system. Therefore, avoid storing expressed breast milk beyond the recommended duration.

Tips To Store Expressed Breast Milk

Below are the points and steps to keep in mind if you intend to store expressed breast milk.

  1. Thoroughly wash your hands with soap and water before and after pumping or expressing the breast milk.  Unclean hands could transfer harmful pathogens to the milk.
  1. Properly wash pumping accessories and all storage containers in hot, soapy water before and after use. Follow the manufacturer’s instructions for effective cleaning. Sterilization of the bottle and pump parts is recommended.
  1. Store the breast milk in small amounts. Two to four ounces is recommended to prevent wastage. Use clean and sterilized bottles to feed breast milk to babies at all times.
  1. Tightly close the container or milk bag’s lid or cap immediately after storing the milk in them. Doing so ensures that the milk doesn’t come in contact with air for long.
  1. Ensure the room temperature is at or below 77°F (25°C) to let the breast milk stay outside the refrigerator.
  1. Use insulated cooler bags with ice packs for a shorter duration. Otherwise, it is best to immediately refrigerate breast milk, especially when the room temperature isn’t conducive for safe storage. Most insulated cooler bags can keep milk good for up to 24 hours.
  1. Place the storage container or bag in a cool towel until you put it in the refrigerator. But ensure that it is only for a few minutes, especially if the room temperature is higher than 77°F (25°C).
  1. Store the breast milk away from direct sunlight in a cool and dry place even when stored at the recommended room temperature.
  1. Store breast milk in the refrigerator if you intend to use it within four days. Otherwise, store it in the freezer to keep it consumable for longer.
  1. Clearly label the milk expression date before you store the milk in the refrigerator or freezer so that you remember to use the milk in order of its expression or pumping date.
  1. Thaw frozen breast milk in the refrigerator gradually. If that’s not possible, place the frozen milk in lukewarm water. Never heat breast milk directly with a flame or microwave. Heating milk can destroy its proteins and antioxidants content.
  1. Never mix freshly expressed warm breast milk with already cooled or frozen milk. It is always best to feed them separately.

Frequently Asked Questions

1. How will I know if breast milk is spoiled?

Spoiled breast milk tastes and smells like spoiled milk (4). Thus, before giving stored milk to your baby, check its taste and smell. If it does not smell right, don’t feed it to your baby. When stored, human milk naturally separates into two layers–a milk layer and a cream top. This separation of layers is normal, and shaking/swirling of the milk recombines the layer. However, if this doesn’t happen, the chances are high that the milk has spoiled.

2. Does thawed breast milk smell or look different from fresh breast milk?

Thawed breast milk may taste different than fresh breast milk. According to experts, thawed breast milk may taste or smell soapy due to fat breakdown in the milk (5).

3. Can you rewarm breast milk twice?

You can reheat milk that has not been used by the baby only once (6). Discard any unused milk that has been reheated.

4. Can I add freshly expressed breast milk to already stored milk?

According to the CDC, “mixing freshly expressed breast milk with already cooled or frozen milk is not advised because it can rewarm the older stored milk. It is best to cool freshly expressed milk before combining it with older, previously cooled, or frozen milk. It is also important to consider storage duration guidelines for breast milk. For example, if combining cooled milk pumped on different days, the duration of storage should be based on when the older milk was first stored (7).”

When breastfeeding isn’t possible, expressed breast milk is a healthy choice for babies. However, its proper storage is essential to ensure the breast milk’s quality. Thus, you should take the necessary measures while storing breast milk. Usually, you can safely store hygienically expressed or pumped breast milk at the recommended room temperature for a short duration. However, refrigeration and freezing are the ideal options if you need to store breast milk for a longer duration. These storage methods help retain breast milk quality and ensure its safety for the baby.

Key Pointers

  • Breastmilk can be stored at room temperature for four hours but longer when refrigerated or frozen.
  • If not stored properly, the expressed breastmilk can be harmful to the baby.
  • Breastmilk storage tips such as hand hygiene and storing it in small amounts are discussed below.


MomJunction's articles are written after analyzing the research works of expert authors and institutions. Our references consist of resources established by authorities in their respective fields. You can learn more about the authenticity of the information we present in our editorial policy.
6. Caregiver’s guide to the breastfed baby; Australian Breastfeeding Association
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Simran Sandhu

Simran Sandhu is a lactation consultant, breastfeeding speaker, and a nurse by profession. She worked in a private hospital at Subang Jaya that prompted her to pursue lactation certification by The International Board of Certified Lactation Consultants (IBCLC). She built a lactation consultation service, ‘Newborn Home Visit’ that provides services for breastfeeding mothers and pregnant mothers.  Simran also offers monthly,... more

Swati Patwal

Swati Patwal is a clinical nutritionist and toddler mom with over eight years of experience in diverse fields of nutrition. She started her career as a CSR project coordinator for a healthy eating and active lifestyle project catering to school children. Then she worked as a nutrition faculty and clinical nutrition coach in different organizations. Her interest in scientific writing... more