Kojic acid is a stable compound that’s non-irritating to the skin when used at the right concentration. According to Marcus, that should be right around 1 percent.
Clean cosmetic chemist and founder of KKT Consultants Krupa Koestline notes a slightly lower percentage. “Most recently the EU [European Union] has recommended a safe limit of 0.7% for Kojic Acid in topical products,” Koestline said. This comes from the concerns surrounding endocrine disruption at a concentration above 0.7%, according to the Scientific Committee on Consumer Safety. These are opinions from the SCCS as the studies on kojic acid concentration are limited, so keep that in mind.
While kojic acid is a generally well-tolerated ingredient, it’s still acid at the end of the day. “For those with very sensitive skin, proceed with caution as kojic acid does have the potential to cause irritation and dryness, as with any acid,” Marcus said.
Also like any acid or exfoliating ingredient, kojic acid should not be used on broken or irritated skin. To reiterate: Avoid use on open wounds, sunburns, rashes, or allergic reactions.