Can Gamma Rays be an Alternative to preservative Agents in Cosmetics?

Abstract

The goal of this work was to experiment and characterize the treatment of finished products with gamma rays, aiming to new cosmetic formulations preservative-free. This paper presents the intermediate results obtained in this framework so far. The research activity was focused on the representative most used cosmetic formulations such as O/W, W/O emulsions and detergents, characterized by different water and lipid phase content, viscosity and additives; among these, colorants were used as probe of stability. The idea behind the project was to exploit the effects of the gamma rays and verify the cosmetic chemico- physical parameters after irradiation, correlating type of formulation, water content and viscosity with formulation stability. This approach has been particularly focused on the situations where one may believe the irradiation less attractive in keeping the product characteristics. In fact azodyes, known to be easily degraded, were found to longer resist at a dose of 10 kGy, when included in high viscosity grade house-formulated and commercial shower gels formulations, in a low water content environment and in presence of antioxidant phenols, such as butyl hydroxyl anysole (BHA). This behavior was found consistent with a mechanism of azodyes degradation involving water hydroxyl radical attack to the azo functional group, reduced by the presence of antioxidants and in high viscosity and ”water-caged” formulations. As a further confirmation of this mechanism, the powder dyes in solid state and no water were found completely stable upon gamma irradiation. These results were also confirmed in emulsion formulations. Viscosimetric evaluation showed that gamma rays treatment did not significantly affect the viscosity grade and emulsion texture in all the formulations. Through these preliminary studies it has been shown that, by adjusting the appropriate formulation ingredients, it is possible to tailor cosmetics products, which maintain their chemicophysical properties and texture, when treated by gamma rays.