A cosmetic composition which provides a semi-permanent, crosslinked film on a keratinous substrate, comprising a film-forming polymer having functional groups capable of cross-linking upon exposure to a cross-linking agent reactive with the functional groups; a cross-linking agent reactive with the functional groups of the film-forming polymer; a dissipatable blocking agent which is operable prior to dissipation, to block the cross-linking agent from cross-linking the functional groups of the film-forming polymer, and which, after dissipation, leaves the cross-linking agent free to cross-link the functional groups of the film-forming polymer.