An area of application for topically applied antioxidants is the anti-aging sector. A clear advantage of the topical application of antioxidants for the skin is that the antioxidants are delivered directly to their target structure, the skin surface, which represents the barrier to the environment, without any loss due to metabolism. However, penetration of such antioxidants into the deeper skin layers is inefficient and almost negligible, and protection is only provided for areas where the substance was applied. In contrast, systemic application (intake via food and/or supplements) enables an accumulation in the complete organism including an increase in antioxidants on the skin surface and in deeper layers of the skin. In systemic applications the protective effect unfolds slowly, but can be detected for a period of several weeks after systemic application of the antioxidants is discontinued. In contrast, topical applications of antioxidants increase the protective potential of the skin immediately. However, the enhanced protective potential declines to its original value within 24 hours unless the topical application is repeated; the quick decline being due to textile contact, washing and showering as well as desquamation of one cell layer of corneocytes per day.
Stress factors – such as irradiation, environmental conditions, illness, inflammation, smoking and alcohol consumption – also produce free radicals in human skin, and thus may decrease the antioxidant level in the skin. A balanced diet – rich, for instance, in fruit and vegetables – is able to increase the antioxidant level of the skin. High levels of antioxidants in the human skin act as an efficient anti-aging strategy, as recently demonstrated (7). Healthy volunteers aged between 40 and 50 years were investigated for the relation of the antioxidant concentration in their skin to skin roughness. Skin roughness was determined by the depth and density of furrows and wrinkles. It was found that individuals with a high concentration of antioxidants in their skin exhibited a lesser degree of skin roughness than individuals of the same age with lower antioxidant levels (8). An additional study investigated the improvement in the skin surface structure after systemic intake of antioxidants and/or the topical application of creams containing antioxidants (9, 10). It was shown that after systemic application of antioxidants, their concentration was increased in the skin. The results obtained concord with other studies, where an increase in antioxidants was found after antioxidant-rich supplementation. After completion of antioxidant treatment, the concentration of antioxidants was detectable in the skin for a longer period of time than after topical application (11).
In addition, antioxidants can have a positive influence on the medical treatment of various diseases, inclu- ding different types of cancer (5). Positive results could be attributed to antioxidants in their naturally balanced compositions and concentrations. Studies investigating the application of synthetic or extracted antioxidants as medical treatments have generated controversial results (12). While a number of studies indicated positive effects after the systemic application of antioxidants – mainly in physiological concentra- tions – studies with high doses of antioxidants (seemingly exhibiting pro-oxidant properties) reported harmful effects. In contrast to the application of antioxidants in supportive medical treatment, the application in cosmetic products (e.g. anti-aging creams) has not produced any harmful effects – apart from a small number of allergic reactions described in several studies (5). Such findings are not surprising as cosmetic products are developed for continuous long-term application with lower antioxidant concentrations than products intended for medical treatment.
In conclusion, the best protection strategy against the harmful action of free radicals is a well-regulated lifestyle with low stress conditions and balanced nutritional habits, including antioxidant-rich food. Taking into consideration the unwholesome nutritional habits of the general population combined with careless exposure to UV radiation, the importance of a regular intake of antioxidants in physiological concentrations has to be emphasized. Recently developed non-invasive techniques for the in-vivo detection of antioxidants and free radicals in the human skin (12) may considerably influence people’s nutritional habits and stress behavior and open up new prospects for the development of antioxidant products.”
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