A skin dressing, particularly a wound dressing, comprises oxidoreductase enzyme and, optionally, peroxidase enzyme, wherein the enzyme(s) are present in hydrated condition, e.g. being present in one or more hydrated hydrogels. The dressing is used by being located on the skin of a human or animal e.g. over a wound. The oxidoreductase enzyme catalyses a reaction that produces hydrogen peroxide from an appropriate substrate, the substrate either being naturally present in body fluids and/or being supplied separately and/or being incorporated into the dressing. The currently preferred oxidoreductase enzyme is glucose oxidase. The catalyses reaction of β-D-glucose substrate to give hydrogen peroxide and gluconic acid. A mixture of oxidoreductase enzyme can undergo reaction (optionally catalysed by the peroxidase enzyme) to produce a variety of species including reactive oxygen intermediates that have antimicrobial properties and that can therefore assist in promoting wound healing.