A dispenser (10, 110, 210, 310, 410, 510, 610, 710, 810) comprising: a body (12, 112, 212, 312, 412, 512, 612) defining a hermetically sealed chamber (20, 120, 220, 320, 420, 520, 620, 720) for receiving a substance; a dispensing tip (16, 116, 216, 316, 416) defining at least one opening coupled in fluid communication with the chamber (20, 120, 220, 320, 420, 520, 620, 720) for providing a path for dispensing the substance from the chamber (20, 120, 220, 320, 420, 520, 620, 720); a one-way valve for preventing the ingress of air or other contaminants through the opening and into the chamber and coupled in fluid communication with the opening of the dispensing tip (16, 116, 216, 316, 416); a plunger (14, 114, 214, 314, 414, 514, 614) within the body (12, 112, 212, 312, 412, 512, 612) for exerting pressure on the substance contained in the chamber (20, 120, 220, 320, 420, 520, 620, 720) upon incremental movement of at least one of the plunger (14, 114, 214, 314, 414, 514, 614) and the body (12, 112, 212, 312, 412, 512, 612) relative to each other for dispensing the substance through the dispensing tip (16, 116, 216, 316, 416) and said one way valve; wherein at least one of the plunger (14, 114, 214, 314, 414, 514, 614) and the body (12, 112, 212, 312, 412, 512, 612) defines at least one drive surface and the other defines at least one recessed surface for receiving therein the at least one drive surface for effecting the incremental movement of the plunger relative to the body; and wherein substance pressurized by the plunger (14, 114, 214, 314, 414, 514, 614) causes the valve member (54, 254, 454, 754, 854) to separate or move away from the valve seat (32, 732) and allow substance to flow out of the dispensing tip (16, 116, 216, 316, 416); characterized in that said one-way valve includes an axially-elongated valve seat (32, 732) and an axially-elongated flexible valve member (54, 254, 454, 754, 854) contacting or interfacing with the valve seat (32, 732) and defining a normally-closed valve opening at the interface of the valve member (54, 254, 454, 754, 854) and valve seat (32, 732); and the axial length of each of valve seat (32, 732), valve member (54, 254, 454, 754, 854) and valve opening formed therebetween is sufficiently long to always maintain a segment of valve member in contact with valve seat when dispensing substance through valve opening, wherein the flexible valve member (54,254,454,754,854) defines a decreasing wall thickness in axial direction from the inside to the outside of the dispenser (10, 110, 210, 310, 410, 510, 610, 710, 810). a body (12, 112, 212, 312, 412, 512, 612) defining a hermetically sealed chamber (20, 120, 220, 320, 420, 520, 620, 720) for receiving a substance; a dispensing tip (16, 116, 216, 316, 416) defining at least one opening coupled in fluid communication with the chamber (20, 120, 220, 320, 420, 520, 620, 720) for providing a path for dispensing the substance from the chamber (20, 120, 220, 320, 420, 520, 620, 720); a one-way valve for preventing the ingress of air or other contaminants through the opening and into the chamber and coupled in fluid communication with the opening of the dispensing tip (16, 116, 216, 316, 416); a plunger (14, 114, 214, 314, 414, 514, 614) within the body (12, 112, 212, 312, 412, 512, 612) for exerting pressure on the substance contained in the chamber (20, 120, 220, 320, 420, 520, 620, 720) upon incremental movement of at least one of the plunger (14, 114, 214, 314, 414, 514, 614) and the body (12, 112, 212, 312, 412, 512, 612) relative to each other for dispensing the substance through the dispensing tip (16, 116, 216, 316, 416) and said one way valve; wherein at least one of the plunger (14, 114, 214, 314, 414, 514, 614) and the body (12, 112, 212, 312, 412, 512, 612) defines at least one drive surface and the other defines at least one recessed surface for receiving therein the at least one drive surface for effecting the incremental movement of the plunger relative to the body; and wherein substance pressurized by the plunger (14, 114, 214, 314, 414, 514, 614) causes the valve member (54, 254, 454, 754, 854) to separate or move away from the valve seat (32, 732) and allow substance to flow out of the dispensing tip (16, 116, 216, 316, 416); characterized in that said one-way valve includes an axially-elongated valve seat (32, 732) and an axially-elongated flexible valve member (54, 254, 454, 754, 854) contacting or interfacing with the valve seat (32, 732) and defining a normally-closed valve opening at the interface of the valve member (54, 254, 454, 754, 854) and valve seat (32, 732); and the axial length of each of valve seat (32, 732), valve member (54, 254, 454, 754, 854) and valve opening formed therebetween is sufficiently long to always maintain a segment of valve member in contact with valve seat when dispensing substance through valve opening, wherein the flexible valve member (54,254,454,754,854) defines a decreasing wall thickness in axial direction from the inside to the outside of the dispenser (10, 110, 210, 310, 410, 510, 610, 710, 810).