A door handle is used to open or close a door. In the United States, door handle can refer to any fixed or lever operated door latch device, including on car doors. The term door knob or simply doorknob tends to refer to round operating mechanisms.door handles are instrumental in the spread of many infections. However, some materials, e.g. brass, copper and silver, are slowly poisonous to many germs. The exact mechanism is not known, but is commonly thought to be via the electrodynamic effect, perhaps by some other electrostatic effect. Brass and copper, for example, disinfect themselves of many germs within eight hours. Other materials such as glass, porcelain, stainless steel and aluminum do not have this effect. Self disinfecting door handles are particularly important in hospitals, but useful in any building.