A one-piece or two-piece ostomy appliance comprising a base plate (1), the base plate comprising an adhesive wafer (11) that comprises a top film (8) and at least one skin-friendly adhesive (9) on a proximal surface thereof, for attaching the base plate to the skin of a user, and a first through-going-hole (5). Further, a convex element (10) is arranged distal to a user-interface of the adhesive wafer and has a second through-going hole (15) of the same diameter as the first through-going hole and being co-axially arranged therewith. The convex element comprises a material which reacts to moisture.