Hyaluronic acid, a popular skincare ingredient, doesn鈥檛 hold 1000 times its weight in water, despite frequent marketing claims.
The ingredient is a humectant, a substance that attracts moisture. Applied topically, , enhance elasticity and reduce wrinkle depth.
But chemists have long suspected that the idea it can hold 1000 times its weight in water is too much of a stretch. , seemingly off the back of research from the 1950s that found hyaluronic acid can trap some water particles, but not necessarily bind to them, which would be required for it to hold the alleged amount of water.
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To set the record straight, Scott Borchers and , both at the University of California, Riverside, carried out so-called differential scanning calorimetry tests. These apply heat to a material so researchers can record changes to its binding properties.
The pair measured the molecule-binding properties of hyaluronic acid and water at a solution of 1 gram of hyaluronic acid to 1000 grams of water, the supposedly significant ratio, to see if the hyaluronic acid formed chemical bonds with the water.
They then compared the results with the thermal changes that take place within pure water during the same differential scanning calorimetry tests, finding that they were essentially indistinguishable. 鈥淚t does still bind water, just not 100,000 per cent by weight,鈥� says Pirrung. Past studies on hyaluronic acid show that .
Each hyaluronic acid unit only has 12 atoms capable of binding to water via hydrogen bonds. If hyaluronic acid could bind to water 1000 times its weight, each unit would have to hold around 22,000 water molecules. In reality, each atom can only bind to three water molecules, making a maximum of 36 water molecules per unit.
at RMIT University in Melbourne, Australia, says that while most chemists probably already thought the claims were overstated, it is useful to explicitly correct them, particularly for consumers who may be misled.
ChemRxiv
