Evidence of the clinical signs associated with skin aging often first appears in the periorbital area and includes wrinkles, eyelid bags, circles around the eye, or a "tired" appearance.1 Very few cosmetic preparations were shown to improve this situation using objective quantitative methods.
The physiological changes observed in chronologic aging skin are barrier function impairment, xerosis, loss of elasticity, slower turnover of epidermal cells and atrophy. There is a progressive reduction in water-binding capacity and changes in cutaneous permeability for chemical substances and increased production of free radicals. Moisturizers decelerate the loss of water from the surface of skin, maintain an appropriate level of skin humidity
and minimize the aspect of fine wrinkles.2
The glycosaminoglycan hyaluronic acid (HA) is a major component
of the extracellular matrix of the skin and plays an important role in the metabolism of the dermis.3 HA is especially
important in the skin because these macromolecules are highly hydrophilic and can bind up to 1,000 times their volume in water. In the skin, this property is likely to be relevant in controlling
tissue hydration.4 Due to these characteristics, HA is often used as a moisturizing agent in cosmetic formulations.
In the skin, HA might also act as a scavenger of free radicals and antioxidants under physiological conditions. Spectroscopic studies
even indicate that a double bond in the D-glucuronic acid unit can form a complex with reactive oxygen species and reduce the toxicity of radicals.5 Furthermore, it plays a major role in the exchange
between fixed tissue cells and blood and in cell migration. Recent studies suggest that HA, via the CD44 receptor, is capable of increasing cell differentiation and cell motility.6 HA also has anti-inflammatory properties and promotes wound healing.7
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