Skip Navigation
New Jersey Agricultural
Experiment Station
Menu
Home Food and Nutrition Publications
Photo: Pump/expressed milk. Photo: A baby drinking mother's milk. Photo: Milk in the front and baby in the back.

Cooperative Extension Fact Sheet FS949

Handle with Care: Guidelines for Safe Storage and Use of Human Milk

  • Luanne Hughes, Family and Community Health Sciences Educator, Gloucester County
  • Michelle Brill, Family and Community Health Sciences Educator Emerita

Breastmilk fully supports a baby's nutritional needs beginning at birth and for the first six months of life. It is easy for your baby to digest and contains immunological properties that cannot be duplicated in infant formula. The American Academy of Pediatrics, the World Health Organization, and other medical authorities recommend exclusive breastfeeding for the first six months of life, and continued breastfeeding, after solid foods are introduced, for one year or more until weaning is mutually decided upon by the parent and baby.

In addition to the well-known benefits to the baby, which include fewer illnesses, sick visits and hospitalizations, exclusive breastfeeding can reduce the child's risk of becoming overweight or obese later in life. Breastfeeding also lowers the risk of developing Type 2 diabetes and certain types of cancer for both mothers and babies. These benefits increase the longer you breastfeed. When you need to be away from your baby, for example when you return to work or school, you can continue to breastfeed if you have a supply of your properly expressed (pumped) and stored breastmilk. Expressed breastmilk must be handled appropriately to retain its nutritional value and natural antibacterial properties, which help it to stay fresh longer.

Getting Started

Before expressing or pumping your milk, wash your hands with soap and water for 20 seconds and dry with a paper towel. Alternatively, use an alcohol-based hand sanitizer containing at least 60% alcohol. Sanitize your counter or tabletop with a disinfectant wipe. Your breasts and nipples do not need to be washed prior to milk expression. Read and follow the breast pump use and cleaning directions provided by the manufacturer and always clean the pump after each use.

Storage Containers

Breastmilk must be stored in clean, food-grade glass or BPA-free plastic containers or bottles with tight fitting lids, or single use storage bags designed specifically for breastmilk. Ordinary plastic storage bags, disposable bottle liners, or formula bottle bags are not intended for storing breastmilk. Containers for breastmilk storage can be washed in hot soapy water, then rinsed and air-dried, or washed in a dishwasher. The containers do not need to be sterilized.

Storage Guidelines

Freshly expressed milk can be stored for up to 4 hours at room temperature; up to 4 days in the refrigerator; and up to 12 months in the freezer. If you do not plan to use the milk within 4 hours or 4 days, freeze it to preserve the most nutrients. Store expressed milk in 2-to-4- ounce portions to limit waste. Leave an inch of airspace at the top of the container to allow milk to expand when frozen.

The Centers for Disease Control and Prevention and the Occupational Safety and Health Administration have determined that human milk is not among the body fluids that require special handling such as universal precautions or storage in a separate refrigerator. It can be stored in a workplace refrigerator where other workers store food. The containers should be placed in the back of the freezer or refrigerator where it is coldest, rather than in the door. Refrigerator temperature should be maintained at 40 degrees Fahrenheit (or 4 degrees Celsius) and freezer temperature at 0 degrees Fahrenheit (or -18 degrees Celsius).

Store newly expressed milk behind older milk so that the older milk is more easily used first. When transporting expressed milk, keep it in an insulated cooler bag with frozen ice packs for up to 24 hours. Containers should be clearly labeled with your name and date when the milk was expressed, or the child's name and the date if the milk will be used in a childcare setting. Talk to your childcare provider about any other requirements they may have for labeling and storing breastmilk.

Using Stored Breastmilk

Always use the oldest milk first. Leave refrigerated bottles of expressed milk in the refrigerator until just before feeding. Thaw frozen breastmilk in the refrigerator overnight, or gradually warm it under lukewarm running water. Breastmilk thawed in the refrigerator must be used within 24 hours or within 2 hours of bringing it to room temperature or warming it. After that, it should be discarded.

Depending on the baby's preference, milk can be served cold, at room temperature, or warmed by immersing the sealed bottle or bag in a bowl of warm water or holding it under warm running water. Avoid heating milk directly on the stove* (see exception below) or in a microwave oven. Microwaves do not heat evenly, and bottles can explode if overheated. Hot spots can burn the baby's mouth. Microwaves also significantly decrease the anti-infective quality of human milk and excess heat can reduce its nutrient quality.

Before feeding, test the milk's temperature by putting a few drops on your wrist. It should feel warm, not hot. Breastmilk separates into layers when frozen as the fat rises to the top. This is normal. Gently swirl the bottle to evenly distribute the temperature and mix in the fat before feeding it to the baby. If the baby does not finish the bottle, leftover milk should be used within 2 hours or discarded.

NEVER refreeze thawed milk. Avoid adding warm milk to already cooled or frozen milk in order to prevent rewarming. Additional milk can be chilled or refrigerated before adding it to previously expressed milk.

Figure 1.

*Occasionally, some mother's stored milk may develop a soapy smell and altered taste due to the action of lipase, an enzyme that breaks down fat into fatty acids. This breakdown of fats aids the infant in digestion and is not harmful, although some babies may refuse to drink the milk if they dislike the taste. To avoid having to discard large amounts of frozen milk, plan to freeze 1 or 2 ounces for pretesting to see if your milk's smell or taste has changed. Do this by thawing the milk after having been frozen for a week and smell it. If it has changed, check to see if your baby will take it. If so, then you may continue to freeze milk, as planned. If the baby will not accept it, you can prevent this change in smell or taste from occurring by scalding (i.e. heat till bubbling around the edges but not boiling) the milk for no longer than 15 seconds to deactivate the lipase before quickly cooling and storing it.

Cleaning Equipment

After feeding, wash the bottle and its parts with soap and hot water before reusing. If you use a breast pump, disassemble the parts after each session and place them in a clean basin with soap and water. Do not wash them directly in the sink to avoid contamination by contact with germs that may be in the sink. Rinse all parts thoroughly under running water and let them air-dry on a clean dishtowel or paper towel. Using clean hands, store dry parts in a clean, protected area.

Returning to Work or School

Following the guidelines above will make it easier to continue to breastfeed when you are separated from your baby or when you return to work or school. Once you become comfortable with the process, you, your baby, and your employer will reap the benefits.

Resources for Breastfeeding Mothers

References

October 2025