EU SCCS Restrictions on Kojic Acid (1%) & Alpha Arbutin (2%): Hydroquinone Release & Thyroid Safety

Kojic acid (5-hydroxy-2-(hydroxymethyl)-4-pyrone) is a fungal metabolite produced by *Aspergillus* species that chelates copper in tyrosinase enzymes to stop melanin synthesis.

In SCCS opinion SCCS/1641/22, toxicologists evaluated systemic dermal absorption models. The data revealed that at concentrations above 1.0%, systemic uptake can reach levels capable of inhibiting thyroid peroxidase (TPO).

Inhibition of TPO interferes with the iodination of tyrosine residues, potentially lowering circulating thyroid hormones (T3 and T4) and prompting compensatory thyroid follicular cell hyperplasia. Consequently, the EU restricted leave-on facial products strictly to a safe threshold of 1.0%.

Alpha Arbutin (4-hydroxyphenyl alpha-glucopyranoside) is a hydroquinone molecule bound to a glucose sugar ring via an alpha-glycosidic bond.

In SCCS opinion SCCS/1642/22, the committee reviewed the chemical stability of this glycosidic bond. Under elevated temperatures (such as humid steam in consumer bathrooms) or acidic pH (<4.5), the bond undergoes chemical hydrolysis, cleaving into free hydroquinone.

Because hydroquinone is completely banned in EU over-the-counter cosmetics due to risks of cellular toxicity and exogenous ochronosis, the SCCS capped Alpha Arbutin at 2% in facial creams and 0.5% in body lotions to ensure free hydroquinone remains below trace safety limits (1 ppm).

While the European Union enforces these strict concentration limits legally, the US FDA does not currently cap Kojic Acid or Arbutin in cosmetic products.

Consumers purchasing products formulated outside the EU should inspect INCI labels to ensure their serums adhere to modern SCCS safety thresholds.