How Long Can Breast Milk Sit Out

“Breast milk is the best milk.” This is an assertion that is repeated often by healthcare professionals, pediatricians, and parents alike. It is no secret that breast milk is rich in antibodies that are essential to protect your loved one until their immune system can combat infections. Colostrum and breast milk have the best composition to sustain an infant and promote their growth and development. As WHO advocates it, babies should be exclusively breastfed for 6 months and continued with solids up to 2 years. This recommendation is difficult to meet when mothers decide to return to a full-time job.

Thankfully, breast pumps have revolutionized the breastfeeding world and made it a smidgen easier for mothers to step away from their babies without having to wean them early. The question that arises now is- how long can you leave breast milk out after warming it up? Pumping, storage, and heating of breast milk is an important subject because of the highly perishable nature of the milk. In this article, we discuss the right technique to store, thaw, and heat milk. More importantly, we emphasize how long your breast milk with stay good if left out.

How to Store and Thaw Breast Milk

Breast milk that has been expressed is the best nutrition that your baby can get if you are unavailable to feed them. Proper storage and heating techniques need to be used so that your baby’s nourishment is healthy and safe for consumption. Once your milk has been expressed in a hygienic way, it can be stored at room temperature, under refrigeration, or in the freezer.

How to Store and Thaw Breast Milk

It is important that you label your containers when you refrigerate or freeze the milk so that you can follow FIFO (First in First Out) and manage your supply well. The best way to avoid wastage is to store smaller quantities and use it as required.

Freshly expressed breast milk keeps well at room temperature between 16°C to 25°C (60°F to 77°F) for 4 to 8 hours depending upon the prevalent room temperature. You can safely store the breast milk in the refrigerator at 4°C/ 39°F for three days. Frozen breast milk is good for up to 6 months if stored at -18°C (0°F). Once you thaw milk from the refrigerator or freezer, it can sit out for a maximum of two hours. It should not be refrozen under any circumstance.

Storing Expressed Milk for Preemies and Babies With Health Issues

Normal storage and thawing guidelines do not apply to infants with health risks or babies who are in the NICU. Bacterial growth in breast milk when left out poses a threat to premature babies who are fragile and high-risk babies. Breast milk that is pumped for premature babies or infants under medical supervision should be consumed within one hour of expressing or it should be refrigerated.

Storing Breast Milk in The Refrigerator or Freezer

It is essential to understand how long can breast milk be out once it is removed from refrigeration. However, it is equally important for parents to understand the right storage techniques as mentioned below:

Storing Breast Milk in The Refrigerator or Freezer

  • Breast milk should be refrigerated or frozen immediately after expressing.
  • You should always use sterilized and clean milk bottles to store the milk. You can even make use of storage bags that are manufactured especially for breast milk. These are BPA free bags.
  • A refrigerated or frozen container with milk can be used to add small amounts of newly expressed milk. For this, the fresh milk should be cooled separately and then added. Do not mix fresh milk with refrigerated or frozen milk.
  • Place the breast milk in the coldest portion of the refrigerator which is mostly at the back where the vents are. Do not use the door for storage because the temperature is inconsistent on this side.
  • To reduce wastage, store your milk in portion sizes of no greater than 60ml.
  • Do not fill the container when you freeze breast milk because the milk expands upon freezing.
  • Store milk in BPA free plastic containers or glass bottles which are refrigerator safe.
  • It is also good to place milk containers away from direct sunlight, heat sources, and windows when leaving out to thaw.

Using and Warming Refrigerated or Frozen Milk

Frozen breast milk will naturally defrost within 12 hours once it is moved inside the refrigerator. Another way to defrost milk is to run it under warm water. If you allow frozen milk to sit at room temperature to defrost, it will spoil and become unsafe for the baby to consume. Do not ever thaw or heat breast milk in a microwave. The radiation kills any nutritional value that breast milk holds. Only fully thawed, breast milk will stay good for 24 hours inside the fridge or 2 hours at room temperature. Any unused milk should be disposed of and not refrozen.

For warming breast milk, place the bottle in a bowl of warm water and allow the temperature to rise. Do not heat it directly and never allow the temperature to cross 40°C. Frozen or stored milk tends to separate with fatty acids and milk fat rising to the top. Gently shake or swirl the bottle around to mix it up adequately.

If you intend to transport expressed breast milk between your workplace and home or daycare, use a cooling box with ice pack.


Remember that bacteria are everywhere. Breast milk is the most potent antibacterial that you can give to your infant provided that it is hygienic and uncontaminated. Once you feed the baby with milk from a cup or a bottle, their saliva mixes with the remaining milk, and it fills with bacteria. This is an important reason why you should dispose of milk that has been partially consumed. The guidelines mentioned above are recommendations made by the CDC, WHO, and FDA to ensure that every infant gets the best nutrition from breast milk, whether it is direct feeding or expressed breast milk. Remember that a healthy and happy baby is a consequence of a mindful parent who knows what they are doing.

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