A breathable electrical heater element for a topical application device such as a wound dressing or a therapeutic heating pad is disclosed. The heater element is formed by photochemically etching a track pattern onto a porous metallised fabric (e.g. nickel coated woven polyester). The heater element has a skin or wound contact layer laminated to the front face of the heater element. An adhesive layer is laminated to the back face of the heater element. The adhesive layer forms an overhang to provide an adhesive border around the wound contact layer to adhere the device to the skin of a patient. Therapeutically active drugs (optionally microencapsulated) may be incorporated into the skin or wound contact layer. Operation of the heater element causes the skin or wound contact layer to release the active drugs to the skin or wound of the patient. Appropriate control of the temperature of the heater element allows control of the release of the active drugs.