A dressing comprising first and second electrodes, an electrical power supply, and further comprising a physiologically or antimicrobially active precursor substance, the dressing being operable, when placed on a skin site to be treated, for a first treatment period, whereby the electrochemical oxidation or reduction of the precursor substance on one of the electrodes to produce a physiologically active oxidised or reduced substance which is capable of diffusing towards the skin site for the treatment thereof is carried out, and subsequently for a first rest period, the electrochemical oxidation or reduction is stopped, wherein subsequent treatment periods followed by rest periods are carried out over time.
