A method for reducing odor, by providing a colloidal dispersion of particles of silica having a particle size of from 3 nm to 100 nm, said particles having ions of one or more metals selected from copper, silver, zinc and iron adsorbed at the particle surface, and bringing at least one of said particles into contact with an odorous compound; and/or providing an aqueous silicate solution containing metal ions selected from ions of copper, silver, zinc and iron, and bringing at least one metal ion-carrying silicate particle formed in the solution into contact with an odorous compound. A composition for use in such a method and a product treated by such a composition.