After forming a dielectric oxide on the rough anode structures, a cathode is needed. An electrolyte acts as the cathode of electrolytic capacitors. There are many different electrolytes in use. Generally, the electrolytes will be distinguished into two species, non-solid and solid electrolytes. Non-solid electrolytes are a liquid medium whose conductivity is ionic. Solid electrolytes have electron conductivity and thus solid electrolytic capacitors are more sensitive against voltages spikes or current surges[citation needed]. The oxide layer may be destroyed if the polarity of the applied voltage is reversed.