A breastshield unit for use in a device for expressing human breastmilk employing underpressure with a breastshield body and a media separation device which separates expressed milk from an underpressure source arranged in the breastshield body, the media separation device having a through-channel which connects first and second openings of the breastshield body. The through-channel has a through-opening, which is enlargeable when subjected to an underpressure from outside. The through-opening is formed by walls which, when subjected to an underpressure from outside, are movable away from each other, largely without stretching, in order to enlarge the through-opening. The breastshield unit permits media separation with minimal dead volume, and with optimized comfort for the mother.
