The present invention relates to a mixture, having a skin-tightening effect, which is made up of: 10 to 80% by weight of a polysaccharide, preferably of an alginate, having a molecular weight of less than 600,000 Daltons, preferably less than 400,000 Daltons and more preferably less than 200,000 Daltons, 15 to 75% by weight of a polyhydroxylated agent selected from sugars and their derivatives, particularly sugar esters and sugar ethers, preferably sorbitol, 3 to 15% by weight of poly(vinyl alcohol) or polyvinylpyrrolidone, and 0 to 25% by weight of cellulose or of a derivative of cellulose, such as carboxymethylcellulose or hydroxymethylcellulose. The present invention also relates to cosmetic compositions which contain this mixture.These cosmetic compositions enable a mechanical smoothing of the surface of the skin to be obtained progressively with great comfort of use and enables a good fixing of make-up products.