According to the cytotoxicity results and in order to completely avoid misinterpretation of results obtained from killing cells by the drug as the depigmenting activity of the drug, we used the maximal concentration of up to 4 μM and 100 μM for HC and arbutin, respectively, in the depigmenting experiments of the present study because of the nontoxic property of thedrugs at these concentrations. The depigmenting results are shown in Fig. 2.