Decontamination gel, consisting of a colloidal solution comprising or consisting of: - 0.1% to 30% by mass, preferably 0.1% to 25% by mass, preferably again 5% to 25% by mass, better 8% to 20% by mass, relative to the mass of the gel, of at least one inorganic viscosifying agent; - 0.01% to 5% by mass, preferably 0.05% to 3% by mass, relative to the mass of the gel, of at least one viscosity variation agent which, when subjected to at least one stimulus, preferably external to the gel, causes a variation in the viscosity of the gel, said stimulus, preferably external to the gel, being selected from chemical stimuli such as a variation in the oxidation-reduction potential of the gel; thermal stimuli such as a variation in the temperature of the gel; physical stimuli such as exposure to an electromagnetic wave; and combinations of two or more of said stimuli, said viscosity variation agent being not a superabsorbent polymer, said viscosity variation agent being selected from the group consisting of polysaccharides, oxidizing compounds, magnetic particles, and compounds the viscosity of which varies when exposed to electromagnetic radiation of different wavelengths; - 0.1 to 10 mol/L of gel, preferably 0.5 to 10 mol/L of gel, preferably again 1 to 10 mol/L of gel, of at least one decontamination active agent different from said viscosity variation agent; - 0.1% to 2% by mass relative to the mass of the gel, of at least one surfactant and preferably of at least one non-ionic surfactant; - optionally 0.05% to 5% by mass, preferably 0.05% to 2% by mass relative to the mass of the gel, of at least one super-absorbent polymer; - and the rest of solvent. - 0.1% to 30% by mass, preferably 0.1% to 25% by mass, preferably again 5% to 25% by mass, better 8% to 20% by mass, relative to the mass of the gel, of at least one inorganic viscosifying agent; - 0.01% to 5% by mass, preferably 0.05% to 3% by mass, relative to the mass of the gel, of at least one viscosity variation agent which, when subjected to at least one stimulus, preferably external to the gel, causes a variation in the viscosity of the gel, said stimulus, preferably external to the gel, being selected from chemical stimuli such as a variation in the oxidation-reduction potential of the gel; thermal stimuli such as a variation in the temperature of the gel; physical stimuli such as exposure to an electromagnetic wave; and combinations of two or more of said stimuli, said viscosity variation agent being not a superabsorbent polymer, said viscosity variation agent being selected from the group consisting of polysaccharides, oxidizing compounds, magnetic particles, and compounds the viscosity of which varies when exposed to electromagnetic radiation of different wavelengths; said stimulus, preferably external to the gel, being selected from chemical stimuli such as a variation in the oxidation-reduction potential of the gel; thermal stimuli such as a variation in the temperature of the gel; physical stimuli such as exposure to an electromagnetic wave; and combinations of two or more of said stimuli, said viscosity variation agent being not a superabsorbent polymer, said viscosity variation agent being selected from the group consisting of polysaccharides, oxidizing compounds, magnetic particles, and compounds the viscosity of which varies when exposed to electromagnetic radiation of different wavelengths; - 0.1 to 10 mol/L of gel, preferably 0.5 to 10 mol/L of gel, preferably again 1 to 10 mol/L of gel, of at least one decontamination active agent different from said viscosity variation agent; - 0.1% to 2% by mass relative to the mass of the gel, of at least one surfactant and preferably of at least one non-ionic surfactant; - optionally 0.05% to 5% by mass, preferably 0.05% to 2% by mass relative to the mass of the gel, of at least one super-absorbent polymer; - and the rest of solvent.