In vacuum therapy for wounds (also called vacuum-assisted wound closure or negative pressure wound therapy), negative pressure is applied to the wound. As with every chronic wound, first the surface and the edges of the wound are cleaned. After that dead tissue and wound fluid are removed. Then the wound is covered with a sterile foam, which itself is covered by an airtight foil attached to the surrounding skin. A tube connects the foam to a vacuum pump with a container for fluid. This system keeps the wound in a constantly moist state, without letting it get too wet.