Arbutin, which is the b-D-glucopyranoside derivative of hydroquinone, is a naturally occurring plant derived compound that has been used for postinflammatory hyperpigmentation. It is effective in the treatment of disorders of hyperpigmentation characterized by hyperactive melanocytes. The action of arbutin is dependent on its concentration. Higher concentrations are more efficacious than lower concentrations, but they may also result in a paradoxical hyperpigmentation. In comparative in vitro studies of various compounds used to improve the appearance of disorders of hyperpigmentation, arbutin was found to be less toxic than hydroquinone. A dose-dependent reduction in tyrosinase activity, as well as melanin content in melanocytes, was also demonstrated
above what % arbutin would hyperpigmentation or paradox darkening be a risk??