Tetrahexyldecyl ascorbate is a stable, fat-soluble form of vitamin C. It is believed that this form of vitamin C can penetrate the skin better than water-soluble forms because its fatty acid component helps aid penetration. Once inside the skin, tetrahexyldecyl ascorbate has the ability to stimulate production of glycosaminoglycans. These are natural sugar molecules that absorb moisture, and thereby help to maintain skin hydration. Tetrahexyldecyl ascorbate is unique in that it is stable in both water and air, lasting as long as 18 months inside the bottle.