Kojic Acid, also known as kojic acid?fungal acid, is an organic acid with antibacterial activity produced by aerobic fermentation of glucose by Aspergillus oryzae at 30?32?°C. Its molecular structure is a substituted γ?pyrone. Among naturally?occurring γ?pyrone compounds, only kojic acid and maltol are well?known.

In 1907, Saito isolated kojic?acid crystals from rice koji. Yabuta gave it the name in 1912, and its chemical structure was confirmed in 1924. Using isotope?tracing techniques, Arnstela (surface fermentation, 1953) and Makuo Kitada (submerged fermentation, 1971) demonstrated that kojic acid is formed by direct oxidation and dehydration of glucose without carbon?skeleton cleavage.

Kojic acid is mainly applied in skin?whitening products, anti?aging preparations, sun?care products, whitening facial cleansers and cosmetic formulations. It exhibits certain antibacterial activity. Gram?negative bacteria are more susceptible to sodium kojate than Gram?positive bacteria, which is opposite to the behavior of most other antibacterial agents.

Kojic acid shows far weaker bacteriostatic potency compared with other antibacterial substances. Its antibacterial property is bacteriostatic rather than bactericidal. Kojic acid has no effect on yeasts, viruses or bacteriophages.