A device comprising a heat-generating component that comprises an alkali metal is provided. The alkali metal in the presence of water at a point of contact of the device undergoes an exothermic reaction to generate heat in situ. The amount of heat generated is proportional to and/or limited by the amount (or moles) of water at the point of contact, and the heat generated is sufficient to achieve an increase in temperature at the point of contact to achieve a therapeutic or beneficial result. In one embodiment, the device is used for reducing sweat production in a subject suffering from excessive sweating or hyperhidrosis. In other embodiments, the device is used to substantially sterilize a surface or render a surface substantially aseptic.