Solubilization of ultraviolet absorbers by cyclodextrin and their potential application in cosmetics

Conventionally, synthetic organic ultraviolet (UV) absorbers, such as octylmethoxy cinnamate (OMC) and avobenzone, have been formulated into cosmetic sunscreens. However, because of their high skin stimulus, alternative products made from natural compounds are required. Although some botanical flavonoids and ferulic acid derived from rice bran are candidates for natural UV absorbers, because of their poor solubility, it has been difficult to formulate these natural compounds into cosmetics. In this work, we confirmed by screening tests that cyclodextrins could make an inclusion complex with the UV absorbers in aqueous solutions. We found by a phase solubility test and Job plot that hydroxypropylated-γ-cyclodextrin (HP-γ-CD) made an inclusion complex with ferulic acid in a stoichiometry of 1:2. In cosmetic applications, the formulation containing the ferulic acid/HP-γ-CD inclusion complex showed a higher sun-cut effect than that containing OMC. Notably, the ferulic acid/HP-γ-CD inclusion complex showed extraordinarily high protection values for UVA, which will be useful for preparing effective and safe sunscreen formulations.