Kojic Acid

A fungal metabolite (produced by Aspergillus and Penicillium species) that inhibits tyrosinase — the rate-limiting enzyme in melanin synthesis. Human clinical trials confirm it reduces hyperpigmentation, melasma, and post-inflammatory darkening; comparable to 4% hydroquinone in some head-to-head studies. Typical OTC concentration: 1–4%. Key limitation: moderate sensitisation potential — some users develop contact dermatitis, making it unsuitable for sensitive skin. Generally well-tolerated at lower concentrations. Available without prescription in both EU and US markets; formulation stability is important as it degrades in light and air.