Storing breast milk

Because what is in your breast milk changes as your baby develops, it is best to use milk as soon as possible after pumping or expressing it. Also, the antioxidant and other protective properties are most important and beneficial to your baby when breast milk is fresh. The protective components of breast milk decrease with refrigeration and freezing.1 However, stored breast milk is the next best thing to fresh breast milk as a complete and nutritious food source for your baby. Stored breast milk is still better for your baby than formula.

Breast milk can be stored and then used in the following ways:2

  • Kept at room temperature for 6 to 8 hours.
  • Kept fresh in a cooler with blue ice [59°F (15°C)] for 24 hours.
  • Stored fresh in the refrigerator [39°F (3.9°C)] for up to 5 days.
  • Kept in a refrigerator freezer [4°F (-15.6°C)] for about 3 to 6 months.
  • Frozen in a separate deep freezer [4°F (-15.6°C)] for about 6 to 12 months.

Milk from both breasts expressed during the same session can be combined in one container. It is best to use a container that holds enough milk for one feeding. You are less likely to have to discard unused milk. Storage containers should be clean and dry. They do not need to be sterile. Plastic bottle liners or small Ziploc bags can be used for storage, held upright in cups. Store milk at the back of the refrigerator or freezer compartment for the most consistent temperature control.

Do not:

  • Refreeze thawed milk.
  • Use thawed (and then refrigerated) breast milk after 24 hours.
  • Use a microwave oven for warming milk. Microwaves heat unevenly, creating hot spots that can burn your baby's mouth and throat.

There is very little research about how safe it is to refrigerate and reuse breast milk left over from a previous feeding. But many experts say it is best to throw away any breast milk left in the bottle after a feeding.

Frozen breast milk will separate because the fat floats to the top. This separation is normal and does not mean that the milk has spoiled or is otherwise unusable. After thawing breast milk, shake the container gently and the fat will redistribute evenly.

When thawing or warming breast milk, run warm water over the storage container (which may be a bottle or a plastic bag) until the milk becomes slushy. You can then heat the container gently in a pot of warm water on the stove until the milk is slightly warm to the touch.

Some people are concerned about bisphenol A (BPA), a chemical in some plastic (polycarbonate) bottles. Research hasn't shown that small amounts of BPA harm humans, but researchers are doing more studies. If you don't want to use this type of baby bottle (which may be marked with the number 7 or the letters "PC" near the recycle symbol), you can use glass or BPA-free plastic bottles.


  1. Hanna N, et al. (2004). Effect of storage on breast milk antioxidant activity. Archives of Disease in Childhood: Fetal and Neonatal Edition, 89(6): F518–F520.
  2. Academy of Breastfeeding Medicine (2004). Human Milk Storage Information for Home Use for Healthy Full-Term Infants, p. 2. New Rochelle, NY: Academy of Breastfeeding Medicine.

Last Updated: May 4, 2009

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