Fibers for generating antimicrobial activity are described. The fibers comprise an enzyme that is able to convert a substrate to release hydrogen peroxide, and an unrefined natural substance that includes a substrate for the enzyme, wherein the enzyme is additional to any enzyme activity able to convert the substrate to release hydrogen peroxide that may be present in the unrefined natural substance. In the presence of sufficient free water, the enzyme converts the substrate to release hydrogen peroxide, which is effective against a wide range of microbes. Wound dressings and compositions comprising the fibers are also described, as is use of the fibers, wound dressings and compositions, particularly for wound healing.
