Kojic Acid

What is kojic acid?

Kojic acid is a natural substance produced by many species of fungi, especially Aspergillus oryzae, which is known in Japan as koji. It has a long history of consumption because it is produced during the fermentation process in the production of a number of foods including miso (soybean paste), shoyu (soy sauce) and sake (R, R).

Is kojic acid stable?

Kojic acid degrades when exposed to UVB radiation, with almost half of the 0.25% kojic acid in an aqueous solution disappearing after 5 hours. Its photostability is enhanced when it is formulated in microemulsions however, especially when the formulation also included linalool, a common ingredient found in perfumes, that protects against oxidation (R).

Kojic acid is relatively stable under conditions of oxidative stress, with only 30% lost after 2 days of exposure to 1.5% hydrogen peroxide (R).

Does kojic acid get absorbed?

Studies on rats have shown that kojic acid is rapidly absorbed after dermal administration, with occlusion enhancing penetration (R). Copaiba oil can enhance the penetration of kojic acid (R), as can the use of delivery systems such as niosomes (R), hydrogels (R) and nanoparticles (R, R, R, R).

In a study on 6 Japanese women, applying 1% of a koijc acid formulation on the cheeks led to detectable plasma concentrations of kojic acid. Repeated exposure also appears to increase the levels of kojic acid in the blood, resulting in higher systemic exposure, than after a single application (R).