The substances having cosmetic activity can be products intended for skin and hair care, such as, for example, humectants such as glycerol, sorbitol, pentaerythritol, inositol or pyrrolidonecarboxylic acid and its salts; artificial tanning agents such as dihydroxyacetone, erythrulose, glyceraldehyde and ??-dialdehydes such as tartral these compounds optionally being combined with colorings; water-