The Fallacy of Hyaluronic Acid Binding a Thousand Times its Weight in Water.

This study re-examined experimental reports and past literature of water binding by the humectant hyaluronic acid, in comparison with another common humectant, glycerol, to critically evaluate the common claim that hyaluronic acid binds a thousand times its weight in water, making it especially suited to be a cosmetic moisturizer. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study aqueous solutions of glycerol and hyaluronic acid. A 0.1 weight % aqueous solution of hyaluronic acid (the putative 1,000 times its weight) is a clear, flowing liquid, comparable to a 10 weight % aqueous solution of glycerol. The melting point and melting heat of fusion of the hyaluronic acid solution were indistinguishable from pure water, while both were reduced for the glycerol solution. This is as expected, as colligative properties of aqueous solutions are proportional to concentration, and the polymer is at a much lower molar concentration than glycerol. There is imperceptible freezing point depression by hyaluronic acid, whereas that by glycerol is as expected. No experimental evidence was found for any special ability of hyaluronic acid to bind water at the claimed level of a thousand times by weight. The origin of the fallacy that it binds water at that level can be traced to older literature that has been misunderstood for the meaning of binding, as compared to other physical properties such as hydrodynamics. [ABSTRACT FROM AUTHOR]