Several categories of ingredients make it possible to maintain hydration:

• Humectant agents which retain water thanks to their hygroscopic capability (having strong affinity for water). Among humectants : Urea , Amino-Acids, Sodium Lactate , Glycerol or Glycerin , Propylene Glycol, PEG (Polyethyleneglycol), and Sorbitol .
• Film-forming agents , substances which together with water form semi-permeable hydrogels, less effective in time than  occlusive agents, but more acceptable agents because they allow the skin to 'breathe'. Among the film forming agents: Collagen, Elastin, DNA, Pectin , Gelatine, Chitosan, the Glycosaminoglycans (like Hyaluronic Acid ).
• Occlusive agents which form an impermeable film on the surface of the skin. Among the occlusive agents: Petroleum Jelly, Paraffin , Vaseline Oil, Sweet Almond Oil ( Prunus Amygdalus Dulcis Oil ), Wheat germ Oil, Shea Butter ( Butyrospermum Parkii Butter ), Beeswax ( Cera Alba ).
• Lyotropic agents which can retain water thanks to their amphiphilic character: these molecules have at the same time an absorbent part (which has affinity for water) and a hydrophobic part (which does not have affinity for water). Among the lyotropic agents: Lanolin and its derivatives, Ceramides, AGE (essential fatty-acids).