It also helps to maintain skin hydration. However, cycles of hydration and dehydration can occur, making continuing care necessary. Massage with oil results in improved skin condition, namely increased hydration and surface lipid content. Hyaluronic acid is a type of GAG that promotes collagen synthesis, repair, and hydration. It regularly conducts testing and research on how hydration and nutrition affect athletic performance. Structural changes are the result of hydration, oxidation, and reduction. Hydraulic lime sets by reaction with water called hydration. It is used to demonstrate the principle of mineral hydration. Clear and copious urine is generally a sign of adequate hydration. It is made by the catalytic hydration of ethylene with sulfuric acid as the catalyst. Combining water with a cementitious material forms a cement paste by the process of hydration. Water acts as a temporary hydration agent. These salts differ in terms of their hydration or crystal habit. Fly ash lowers the heat of hydration allowing thicker placements to occur. Racemic malic acid is produced industrially by the double hydration of maleic anhydride.