Chapter 37: Kojic Acid

INTRODUCTION

SOURCE

Kojic acid (5-hydroxy-2-hydroxymethyl-γ-pyrone or 5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one) is a fungal metabolite of several species of bacteria, including Acetobacter, Penicillium, and Aspergillus, particularly Aspergillus oryzae, a fungus used for centuries in Asia in the production of soy sauce, miso, and sake.² Derivatives of kojic acid have been reported to display enhanced efficiency via greater skin penetration.³

HISTORY

Kojic acid was discovered as a fungal natural product in 1907.⁴ It was used widely in cosmetic agents, particularly in Japan from 1988 to 2003, for its capacity to reduce pigmentation.^5–7 Kojic acid was deemed a “quasi-drug” and banned from the market in Japan by the Ministry of Health, Labor and Welfare in 2003 and subsequently in Korea and Switzerland due to safety concerns stemming from animal test results suggesting mutagenicity. Some countries have reportedly since reintroduced it as a skin-lightening agent, but it remains excluded in others.⁸

CHEMISTRY

Kojic acid inhibits tyrosinase activity, mainly by chelating copper, leading to a cutaneous whitening effect.⁹ It is also believed to act by inhibiting the tautomerization of dopachrome to 5,6-dihydroxyindole-2-carboxylic acid.^5,10 In addition, the preservative and antibiotic activities of this agent contribute to extending product shelf life.¹¹ Such stability is one of the advantages of kojic acid in comparison to hydroquinone (HQ) as well as other skin-lightening ingredients (Table 37-1).¹² The efficacy of kojic acid in achieving such an effect is similar to that of HQ, the gold standard but controversial depigmenting agent.^13,14 However, while kojic acid yields greater stability than HQ, the fungal derivative does have labile oxidative properties, which are enhanced by light and heat exposure. Therefore, kojic acid is included in cosmetic formulations through its dipalmitic ester (as kojic dipalmitate).¹⁵

ORAL USES

Kojic acid is widely used as a food additive for preventing enzymatic browning, and to promote reddening of unripe strawberries.¹⁶ It is used in Asia as a dietary antioxidant.^17,18

TOPICAL USES

Kojic acid is second only to HQ in effectiveness as a skin-lightening agent in topical over-the-counter products, ...