Kojic acid (inci)

Kojic acid is a herbal agent used in cosmetic formulations. Kojic acid is a metabolic product of Aspergillus species used in the fermentation of malted rice used in the production of sake (rice mould - Aspergillus oryzaea = Japanese Koji).

Koji acid has the molecular formula C6H6O4 , consists of yellowish crystals and has a caramel-like odor. The substance is easily soluble in water and ethanol but insoluble in acetone. Kojic acid forms coloured, poorly soluble chelate complexes with some heavy metal ions (Fe3+, Cu2+, Zn2+).

The substance acts as an antioxidant (inhibits reactions promoted by oxygen, thus preventing oxidation and rancidity of ingredients). Furthermore, Kojo acid has an inhibiting effect on melanin formation (tyrosinase inhibitors). Preparations with koijic acid are widely used in Asian countries to lighten the skin. They are prohibited in Switzerland.

Alternative active ingredients which serve to "lighten the skin" are: arbutin, hydroquinone, azelaic acid, vitamin C, niacinamide, mulberry extracts (also containing arbutin), liquorice root extracts (see Liquiritiae radix).

1. Kim AJ et al (2012) Metabolomics-based optimal koji fermentation for tyrosinase inhibition supplemented with Astragalus radix. Biosci Biotechnol Biochem 76:863-869.