Closed system pump has a protective barrier between the milk collection unit and the pump unit which prevents any risk of milk contamination or milk build - up in the pump unit. (electricbreastpumpwomen.com)
And it also comes with a lid to keep dust out to prevent milk contamination. (momdiscuss.com)
Feeding causes bacteria to transfer from the baby's mouth to the bottle, which leads to milk contamination during long - term storage. (newkidscenter.com)