New combined treatment of hypermelanosis: analytical studies on efficacy and stability improvement

The aim of this work was to evaluate the synergy between different lightening agents when associated; depigmenting activity was tested in vitro by monitoring the appearance of dopachrome, an intermediate in the melanogenesis process. The results obtained were compared with the depigmenting activity of each single compound, keeping the same global concentration of inhibitor. Our studies showed that the combination of hydroquinone and kojic acid had a synergistic effect, and that the maximum inhibiting action was achieved with an equimolecular mixture. This result could serve in the cosmetics field to prepare skin-lightening formulations that are less irritant. We also investigated the feasibility of complexing hydroquinone with cyclodextrin and evaluated the effectiveness of the complex obtained in the treatment of hyperpigmentation.