A polysilicone base for medical and cosmetic compositions includes a dimethicone fluid, a volatile cyclosiloxane, a silicone elastomer, and nanoparticulate silica. The polysilicone base may also include one or more therapeutic agents for reducing the formation and appearance of scar tissue at the site of a wound. The polysilicone base is spreadable, but does not run off of the wound site. The polysilicone base is phase-stable, in that it does not separate into phases.