Kojic acid (5-hydroxy-2 hydroxymethyl-4-pyrone) is a hydrophilic fungal derivative acquired from Acetobacter, Penicillium, and Aspergillus species, which reduces pigmentation through the inhibition of free tyrosine kinase production. Additionally, it is a potent antioxidant.

Uses

Kojic acid is often utilized as a component of cosmeceutical formulations in Asia and the United States at concentrations ranging from 1% to 4%. There are no randomized controlled trials comparing the efficacy of kojic acid to other cosmeceuticals. However, given that kojic acid and HQ both function through inhibition of tyrosinase, combining the two may result in augmentation of efficacy. This was demonstrated in one study in which Chinese women with epidermal melasma were treated with 2% kojic acid gel compounded with 10% glycolic acid and 2% HQ on the active side of the face. The other control side of the face was treated with the same combination without kojic acid. While visible improvement was noted on both sides of the face, 60% of lesions treated with kojic acid versus 47.5% of those in the control group showed over 50% improvement of melasma. 

Adverse effects 

Given these results, the addition of kojic acid may be beneficial in patients who do not respond to HQ alone.Adverse effects reported in this study were observed regardless of kojic acid use, and included stinging, erythema, and mild exfoliation.