A person who is lactating may want to express and store breast milk for many practical reasons, including for babies who go to day care or who do not latch or suck well. It is safe to store breast milk as long as parents or caregivers follow established safety guidelines.

A person can store fresh and frozen breast milk as long as they follow the safety guidelines regarding temperature and storing duration.

This article outlines how to store fresh and leftover breast milk, and how to thaw and store frozen breast milk.

We also provide information on how long breast milk will safely keep, and provide tips on how to prepare stored breast milk.

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A person who is lactating can express breast milk by hand or with a breast pump.

Freshly expressed milk can last up to 4 hours at room temperature (77°F).

It is then possible to store remaining fresh milk in a special breast milk storage bag or sterilized container using one of the following methods:


People can store the milk in a refrigerator at a temperature of 40°F or lower for up to 4 days. If the temperature is higher inside the fridge, or a person does not know the temperature, they should use the milk within 3 days.


People can store the milk in a freezer at a temperature of 0°F or lower. While it is optimal to use frozen breast milk within 6 months, a person can store fresh breast milk in a freezer for up to 12 months.

It is important to express and store fresh breast milk in safe and sterile conditions. Some tips for this include:

  • washing the hands thoroughly before expressing milk
  • ensuring that breast pump kits are clean and discarding any tubing immediately if it shows signs of mold
  • cleaning and sterilizing anything required for storing the milk, including milk storage containers, the refrigerator, and the freezer
  • only storing breast milk in glass or food-grade plastic containers with airtight lids
  • avoiding storing milk in bottles with the recycling symbol number 7, which indicates that the bottle contains toxic BPA plastic
  • clearly labeling breast milk with the date the lactating person expressed it
  • avoiding storing breast milk in the door of the refrigerator, as doing so can expose the milk to temperature changes when the door opens and closes

After a baby has finished feeding, people should use any leftover breast milk within 2 hours. Beyond this period, it is advisable for people to discard any leftover milk.

A person can store breast milk in a freezer for up to 12 months, though 6 months is preferable as an upper limit.

Individuals should not thaw breast milk in a microwave, as this causes hot spots that can burn a baby’s mouth. Microwaving can also destroy nutrients.

Tips for safely thawing breast milk include:

  • thawing the oldest milk first, as the quality of breast milk can decrease over time
  • thawing the milk in a container of warm or lukewarm water or under running lukewarm water
  • thawing the milk by placing it in the refrigerator overnight
  • using the milk within 24 hours of thawing in the refrigerator

A parent or caregiver should never refreeze breast milk once it has thawed. Harmful bacteria can grow in the milk after thawing.

To prepare stored breast milk for feeding, a person may wish to keep it at the refrigerated temperature as a baby can consume it cold, or they can warm it.

Tips for warming breast milk include:

  • placing the sealed milk container into a container of warm water or holding it under warm running water
  • testing the temperature of the milk by pouring some onto their wrist to ensure it is not hot
  • swirling the milk to ensure the fats are mixed, as they may have separated
  • transferring the milk to a bottle
  • using any leftover milk within 2 hours of feeding and discarding any that the baby does not consume

It is safe for a person to store breast milk as long as they follow the appropriate safety guidelines.

People can store freshly expressed milk in a sterile food-grade container for 4 hours at room temperature, up to 4 days in the refrigerator, or up to 12 months in the freezer. However, depending on the fridge temperature, people may need to use the milk within 3 days. Additionally, while it is acceptable to store fresh milk for up to 12 months in the freezer, up to 6 months is the optimal duration for the best quality.

A person should never thaw frozen milk in a microwave, as this reduces the nutrient content and can burn a baby’s mouth. Instead, slowly warm the milk in a container of warm water or leave it to thaw in the refrigerator overnight.

It is important that people use leftover milk from feeding within 2 hours and then discard the remainder. Parents or caregivers should never reuse milk from a past feeding and should never refreeze thawed milk. Doing either can expose the baby to potentially harmful bacteria.