A recent paper published in the Journal of Oral Tissue Engineering (in Japanese) explored the efficacy and safety of two commonly used cosmetic preservatives to inhibit microbial growth: methyl para-hydroxybenzoate (aka methylparaben) and phenoxyethanol. Here, the relationship between efficacy and cytotoxicity was investigated from a cosmetic safety management perspective.
According to the article abstract, as might be expected, efficacy tests showed a decrease in the survival rate of microorganisms and a different tendency with each type of bacteria and preservative. When the two preservatives were combined, a synergistic effect was observed.
In cytotoxicity tests, cell survival rate in the methyl para-hydroxybenzoate solution decreased gradually at first, then markedly dropped with an increase in preservative concentration. In phenoxyethanol, a proportional decrease was observed. In both, the cell survival rate decreased slightly more than in phenoxyethanol alone.
This underlines the significance of variations in the safety, efficacy and even the mechanisms of action for individual and combined preservative systems. It also reiterates what authors in our March 2018 edition of Cosmetics & Toiletries identified:
"Designing formulations with maximum preservation efficacy using minimum preservative quantities is vital for several reasons...This strategy requires leveraging the right preservatives and levels for given formulation designs."
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