Sodium levulinate is the salt of levulinic acid, a synthetic organic acid that helps condition and soften skin. Sodium levulinate is sometimes part of preservative blend because it exhibits antimicrobial action, although this is more common in food than for cosmetics.
The levulinic acid component can be transformed by naturally-occuring microbes into other helpful substances, including the moisturizing ingredient trehalose.
References for this information:
Natural Microbiology, December 2017, pages 1,624-1,634
Journal of Food Science, June 2008, pages M230-M244
Lebenson Wiss Technology, December 2004, pages 865–871
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