Reduced-pressure medical dressings, systems, and methods involve a dressing with a first barrier layer that desolidifies when exposed to a fluid—typically a liquid—to form a treatment aperture in the first barrier that is used to deliver reduced pressure to a tissue site. The first barrier layer is formed from a desolidifying material. The system includes a drape covering a second surface of a manifold and a portion of the patient's epidermis to provide a substantially sealed space containing a manifold and the first barrier layer. Other systems, dressings, and methods are also disclosed.