Is expressed human milk sterile?

• A. Yes
• B. No
• C. Sometimes
• D. Only when heated

Answer: (B)

Expressed human milk is not sterile. Even from healthy mothers, milk contains native bacteria that live in the mammary ducts, and the act of expressing, handling, and storing milk with equipment or containers can introduce bacteria from skin, air, or the environment. Because of these factors, you shouldn’t assume the milk is free of viable microorganisms unless it has undergone a true sterilization process, which standard expression does not provide. In practice, donor human milk is pasteurized to reduce microbial load, but pasteurization is not the same as sterilization and does not guarantee sterility; there is still a risk of contamination after pasteurization. Hence, expressed human milk is not sterile.