Breast Cancer Awareness Month naturally draws attention to breast health, diagnosis, treatment and survivorship. It can also open the door to another conversation involving the breast that receives far less attention from a food safety perspective: The safe handling of expressed breast milk.

Breast milk provides important nutrition and immune protection for infants, and breastfeeding is widely recognised as beneficial for both mother and child. However, once milk is expressed, whether by hand or with a pump, it also becomes a food that must be collected, stored, transported and served safely. However, this does not mean expressed breast milk should be viewed as inherently risky.

A 2026 scoping review examining reported bacterial and fungal infections associated with expressed breast milk found that such infections appear to be rare and occurred predominantly among very premature and very low birth-weight infants. However, the review also identified breast pumps, storage and the handling environment as possible contamination pathways.

For parents expressing milk at home, the message is therefore similar to that applied to other foods: good nutrition and food safety must work together.

Expressing Milk Introduces New Handling Steps

Direct breastfeeding limits many of the handling steps that occur when milk is pumped, stored and later fed to an infant. Expression introduces hands, pump equipment, tubing, bottles, storage bags, refrigerator surfaces and feeding equipment into the process. Each additional contact point creates an opportunity for microorganisms to enter the milk.

A 2025 study examining milk expressed at home by 52 women found that pumping and hygiene practices influenced the bacterial populations present in expressed milk. Handwashing before pumping was practised by only 22 per cent of participants and was associated with lower bacterial counts. Milk expressed using appropriately cleaned collection kits also contained lower bacterial counts than milk collected using less thoroughly cleaned equipment.

Earlier research involving mothers of very low birth-weight infants similarly found higher bacterial contamination rates in milk collected using pumps compared with manually expressed milk in that particular study population, particularly when pumping occurred at home.

These findings do not mean breast pumps are unsafe. They demonstrate that the equipment must be treated as food-contact equipment. Hands should be washed before expressing or handling milk, and pump parts that come into contact with milk should be cleaned properly after use. Pump tubing and equipment should also be inspected regularly, particularly for moisture or mould. Current public-health guidance recommends replacing mouldy tubing rather than attempting to continue using it.

The Storage Clock Starts After Expression

One of the most important questions after milk is expressed is how long it can be safely stored. Current guidance from the United States Centers for Disease Control and Prevention states that freshly expressed milk for healthy full-term infants can generally remain at room temperature of 25°C or colder for up to four hours. It may be refrigerated at approximately 4°C for up to four days. When frozen at approximately -18°C or below, using the milk within six months is considered best for quality, although storage for up to 12 months is considered acceptable.

These numbers should not be interpreted as targets that must always be reached. Earlier refrigeration is preferable when milk will not be used immediately, particularly in hot environments. This is especially relevant in Jamaica. A room that feels comfortable may still be warmer than 25°C, particularly during daytime hours or in spaces without air conditioning. The phrase “room temperature” therefore should not be interpreted as permission to leave expressed milk on a countertop indefinitely.

Where refrigeration is available, milk should be placed into clean, food-grade containers or breast milk storage bags with secure closures. Disposable bags that are not designed for milk storage should not be used as substitutes. Containers should also be labelled with the date the milk was expressed so that the oldest milk can be used first.

Where To Store Inside Refrigerator

Breast milk should not be stored in the refrigerator door. The temperature in the door fluctuates more frequently as the refrigerator is opened and closed. Storing milk farther inside the refrigerator provides more consistent cold storage. Current CDC guidance recommends keeping the refrigerator at 4°C or below and the freezer at -18°C or below.

Parents who express milk regularly should also avoid overcrowding the refrigerator to the point where cold air cannot circulate effectively. Milk should be stored securely and away from raw foods or packages that may leak. Breast milk may be an infant’s food, but the refrigerator remains a shared food environment.

Mixing Milk Requires Some Thought

Parents sometimes express milk more than once during the day and want to combine the different portions. Freshly expressed warm milk should not immediately be poured into milk that has already been chilled or frozen because doing so may rewarm the older milk. Current guidance recommends cooling the freshly expressed milk before combining it with previously chilled milk.

When milk expressed at different times is combined, the storage period should be based on the oldest milk in the container. This is an important food safety principle that extends beyond breastfeeding: Combining something fresh with something older does not reset the storage clock.

Thawing and Warming Need Their Own Rules

Breast milk does not need to be warmed before feeding. Some babies will drink it cold or at room temperature. If warming is preferred, refrigerated or frozen milk can be placed in warm water or held under lukewarm running water. Frozen milk can also be thawed gradually in the refrigerator.

Microwaving is not recommended. One major concern is uneven heating. Microwaves can produce hot spots that may burn an infant’s mouth even when the bottle does not feel excessively hot from the outside. A recent experimental study of microwave thawing also demonstrated uneven temperature distribution within human milk, supporting concerns about inconsistent heating. Current CDC guidance additionally advises against microwaving because excessive heating may affect some components of human milk.

Once previously frozen milk has completely thawed in the refrigerator, it should generally be used within 24 hours. Once breast milk has been brought to room temperature or warmed, it should be used within two hours. Completely thawed milk should not be refrozen. These time limits matter because warming removes the protection provided by cold storage and allows microorganisms present in the milk to multiply more readily.

What Happens After Baby Starts Drinking?

One of the most easily overlooked food safety considerations occurs after the bottle reaches the baby. Once an infant begins feeding, microorganisms from the baby’s mouth can enter the remaining milk. The unfinished portion should therefore not be placed back into storage indefinitely. Current guidance recommends using milk left after a feeding within two hours after the baby has finished. After that period, the remaining milk should be discarded.

For parents who find themselves repeatedly discarding milk, the solution may be smaller portions rather than stretching the storage time. Milk can be stored and offered in quantities closer to what the baby normally consumes, with additional milk provided if needed. Breast milk may be precious, particularly when expressing it requires considerable time and effort; however, avoiding waste should not come at the expense of safe handling.

Power Outages Change the Conversation

Electricity interruptions introduce another important consideration for families who store expressed milk. During a power outage, refrigerator and freezer doors should be kept closed as much as possible. According to current emergency guidance, an unopened refrigerator can generally maintain safe temperatures for about four hours. A full unopened freezer can maintain its temperature for approximately 48 hours, while a half-full freezer may remain sufficiently cold for around 24 hours.

The condition of frozen breast milk should be checked when electricity returns. Milk that still contains ice crystals can generally be refrozen. If it has completely thawed but remains cold, it should be refrigerated and used within 24 hours or discarded. Milk that has fully thawed should not be refrozen.

Families who store substantial quantities of expressed breast milk may therefore benefit from keeping frozen gel packs, an insulated cooler and an appliance thermometer available as part of household emergency preparation. A freezer full of carefully expressed breast milk represents time, nutrition and effort. A little preparation before a power outage can help protect that investment.

Breast Cancer Treatment Adds Another Layer

Breast Cancer Awareness Month also raises a more complicated question: Can someone undergoing breast cancer treatment continue to breastfeed? There is no single answer that applies to every treatment.

Many anticancer medicines can pass into human milk, and recommendations depend on the drug, dose, timing and treatment plan. Reviews of breastfeeding during breast cancer care advise that breastfeeding generally be interrupted during active chemotherapy, hormonal therapy and many targeted treatments because of the possibility of drug exposure to the infant.

More recent recommendations from breast cancer specialists similarly emphasise that lactation needs to be considered as part of the overall treatment plan rather than handled separately from oncology care. This is an important distinction. A mother should not simply calculate the time since her last chemotherapy infusion and decide independently that her milk is safe. Different medicines remain in the body for different periods, and treatment combinations further complicate the decision.

A mother diagnosed with breast cancer while breastfeeding should discuss feeding plans with her oncologist, paediatrician and, where available, a qualified lactation professional.

About the Author

Allison Richards is a food safety communicator, certified trainer and the founder of The Food Safety Girl®, a consumer awareness platform promoting food safety in Jamaica and the Caribbean. She is the Caribbean Chapter Director for Women in Food Safety (WIFS) and host of The Big Bite Food Safety Show®. With over 15 years of experience in food safety regulation, she is committed to public education and consumer empowerment. Through public education initiatives, including free community webinars, she continues to create space for learning, dialogue, and practical food safety awareness.

Allison Richards thefoodsafetygirlja@gmail.com.