A powdery composition C1 contains for 100% of the mass: 5 to 70 mass % and more particularly 10 to 50 mass % of at least one compound of formula (I): R—O-(G)x-H, wherein R is a linear saturated aliphatic radical including 12 to 22 carbon atoms, G is the remainder of a reducing sugar selected from the group including glucose, xylose and arabinose, and x is a decimal number greater than or equal to 1 and lower than or equal to 10; 95 to 30 mass % and more particularly 90 to 50 mass % of one or more alcohols of formula (II): R′—OH, wherein R′ is a linear saturated aliphatic radical including 12 to 22 carbon atoms identical to or different from R as defined in formula (I), wherein at least 90 vol % of the particles have a diameter lower than or equal to 250 micrometers, more particularly a diameter lower than or equal to 150 micrometers.