Thus, the present invention provides a composition in powder form comprising highly dispersed silica particles, polymethylsiloxane particles, and at one or both of a cationic surfactant and an antimicrobial substance, wherein at least 25 % by weight of the cationic surfactant is present in primary polymethylsiloxane particles carrying the cationic surfactant on their surface and/or in agglomerates of these primary particles, and/or at least 25 % by weight, of the antimicrobial substance is present in primary highly dispersed silica particles carrying the antimicrobial substance on their surface and/or in agglomerates of these primary particles.