Process useful for forming a coating based on at least one active ingredient at the surface of a substrate, in particular an organic substrate, characterized in that it comprises at least the stages consisting in: having available an aqueous dispersion of nanoparticles or of a mixture of nanoparticles having a core formed in all or part of at least one active ingredient and coated with an outer layer formed of at least one hydrophilic polymer, said active ingredient(s) and hydrophilic polymer(s) being combined in an active ingredient(s)/hydrophilic polymer(s) ratio by weight varying from 0.2 to 0.4, said hydrophilic polymer having a molecular weight of greater than 10 000 g/mol, bringing said surface of said substrate into contact with said aqueous dispersion, and exposing said substrate obtained on conclusion of the preceding stage to conditions propitious to the formation, at the surface of said substrate, of a polymeric film formed of said nanoparticles, stage being a drying stage, said nanoparticles of stage being prepared according to a process comprising at least the stages consisting in: - having available an organic phase, such as methylethylketone or cyclohexane, comprising said active ingredient in the dissolved state, - having available an aqueous phase comprising at least one hydrophilic polymer, - adding the organic phase to the aqueous phase under conditions propitious to the formation of an emulsion of the type consisting of an organic phase in an aqueous phase and in the presence of at least one surfactant capable of stabilizing said emulsion, - carrying out a thermal quenching of the emulsion thus obtained in order to form said nanoparticles, and - isolating said nanoparticles. having available an aqueous dispersion of nanoparticles or of a mixture of nanoparticles having a core formed in all or part of at least one active ingredient and coated with an outer layer formed of at least one hydrophilic polymer, said active ingredient(s) and hydrophilic polymer(s) being combined in an active ingredient(s)/hydrophilic polymer(s) ratio by weight varying from 0.2 to 0.4, said hydrophilic polymer having a molecular weight of greater than 10 000 g/mol, bringing said surface of said substrate into contact with said aqueous dispersion, and exposing said substrate obtained on conclusion of the preceding stage to conditions propitious to the formation, at the surface of said substrate, of a polymeric film formed of said nanoparticles, stage being a drying stage, said nanoparticles of stage being prepared according to a process comprising at least the stages consisting in: - having available an organic phase, such as methylethylketone or cyclohexane, comprising said active ingredient in the dissolved state, - having available an aqueous phase comprising at least one hydrophilic polymer, - adding the organic phase to the aqueous phase under conditions propitious to the formation of an emulsion of the type consisting of an organic phase in an aqueous phase and in the presence of at least one surfactant capable of stabilizing said emulsion, - carrying out a thermal quenching of the emulsion thus obtained in order to form said nanoparticles, and - isolating said nanoparticles. - having available an organic phase, such as methylethylketone or cyclohexane, comprising said active ingredient in the dissolved state, - having available an aqueous phase comprising at least one hydrophilic polymer, - adding the organic phase to the aqueous phase under conditions propitious to the formation of an emulsion of the type consisting of an organic phase in an aqueous phase and in the presence of at least one surfactant capable of stabilizing said emulsion, - carrying out a thermal quenching of the emulsion thus obtained in order to form said nanoparticles, and - isolating said nanoparticles.