Maintaining our skins internal moisture balance is essential for cellular communication, skin regeneration and barrier functioning. However, this is not the only way Hyaluronic acid helps our skin stay moisturised. When added to skin care products, Hyaluronic Acid traps water molecules from the product and pushes them into the skin cells. Cells on the surface of our skin soak in this moisture and in doing so increase in size. This swelling effect seals any gaps that had formed from older cells drying out and in turn this improves our skins barrier functioning. Further, these outer cells are not bound by the same rules as the live tissue of our dermis and because of this they can soak up much more water than they need. These now super-hydrated cells give the skin a much smoother and more radiant look, erasing fine lines and wrinkles as they swell.
The water/hyaluronic acid relationship is interesting and often discussed in cosmetic science circles. Many people quote Hyaluronic Acid can hold up to 1000 times its weight in water, but it is less often discussed how this could be so or whether it really matters. Maybe Hyaluronic Acid has one thousand hands that hold onto one water molecule each. Or maybe Hyaluronic acid sucks up water like a sponge - absorbing it into its polymeric self. Maybe though it does it do neither and instead has another way of carrying such a huge water load to our skin. Maybe only 500 times its weight in water would do anyway...
Whatever the answer it is undeniably true that Hyaluronic Acid is a good water carrier and its success is due to its chemistry.
Hyaluronic Acid is a sugar-like ingredient made by combining D-glucoronic Acid and N-Acetyl-D-glucosamine into what chemically is called a disaccharide. These disaccharides have lots of molecular 'hands' with which to hold or bind with water and if you consider that each disaccharide in Hyaluronic Acid is bound to two others in chains that can be thousands of units long you can see where its legendary holding capacity may come from. The only issue with this theory is that these disaccharides are quite heavy and don't have enough hands to account for the whole molecule 'holding' so much water - maybe only enough for 10-15 times its weight, that's it, less exciting!
It turns out that rather than 'hold' each water molecule, Hyaluronic Acid creates a frame rather like a fishing net. From this frame hundreds if not thousands of water molecules can be anchored. So the Hyaluronic Acid does 'hold' some water via direct bonds but then relies on the natural tendency of water molecules to 'hold' or attract a few more molecules of their own. It doesn't take long before a giant hyaluronic-bound water-gel is formed and that's where the 1000 times numbers come from.
The idea of Hyaluronic Acid as a structure builder is supported by good scientific evidence. Scientists have also found that Hyaluronic Acid's water-binding capacity is influenced both by pH and concentration thus meaning that different formulations will create different opportunities for Hyaluronic Acid to combine with and deliver water to the skin. In addition to its water binding capacity Hyaluronic Acid has also been found to act as an osmotic pump, one that can deliver water-soluble actives deep into the skin thus improving their chances of hitting their biological target. Finally, researchers have investigated the role that Hyaluronic Acid plays as water-glue - a substance that not only delivers water into the skin but that ensures it stays there!
After looking more closely at the structure and action of Hyaluronic acid is it seems less important to identify and obsess over its exact water holding capacity and more important to focus on applying it in a way that allows for its many and varied benefits to be best utilised. There is no doubt that Hyaluronic Acid can both hydrate and help moisturise the skin so all that is left is to get some into the basket to try!