The preservatives added to cosmetics and quasi-medicines inhibit the growth and bacteriostasis of microorganisms. However, since they also have effects on cells, their safety and effects on the human body are of marked concern. In this study, therefore, the relationship between the preservative efficacy and cytotoxicity of preservatives was basically investigated from the viewpoint of cosmetic safety management. Two common preservatives, whose skin stimulation or contact dermatitis tests have been reported, were used. Especially, the inhibition of bacteria growth and bacteriostasis of the very common methyl para-hydroxybenzoate were examined in comparison with phenoxyethanol. The preservative efficacy tests showed a decrease in the survival rate of microorgan-isms and a different tendency for each type of bacteria and preservative. In the case of concurrent use, a synergistic effect was observed. On the other hand, in cytotoxicity tests, the cell survival rate in the methyl para-hydroxybenzoate solution decreased gradually at first, and then markedly dropped with an increase in the concentration of the preservative, contrarily to the proportional decrease in the phenoxyethanol. In the case of concurrent use, the cell survival rate in the phenoxyethanol solution decreased slightly more than on single use, because of the effect of the initially added methyl para-hydroxybenzoate. In this study, it was found that quite different tendency existed in the relationship between the preservative efficacy and cytotoxicity of each preservative.
Key words: cosmetic, preservative, skin stimulation, preservative efficacy, cytotoxicity
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