A skin dressing comprising first and second electrodes, an electrical power supply not electrically connected to either or both of the first and second electrodes, and further comprising a physiologically or antimicrobially active precursor substance, the dressing being operable, when placed on a skin site to be treated, to connect the electrical power supply to both the first and second electrodes, thereby to trigger the electrochemical oxidation or reduction of the precursor substance on one of the electrodes to produce a physiologically or antimicrobially active oxidized or reduced compound which is capable of diffusing towards the skin site for the treatment thereof.
