Evaluation of interaction between natural antioxidants and chemical sunscreens aiming the photoprotective efficacy

To promote broad-spectrum protection, the most sunscreen products combine two or more filters for UVA and UVB. The photoprotective efficacy may be affected by the instability of the chemical combination and it is possible to use natural photo-stabilizing substances with antioxidant activity, adding value to the formulation. This study aims to evaluate the thermal behavior of the filters avobenzone ( BMBM / Butyl Methoxydibenzoylmethane ) and octyl methoxycinnamate ( EHMC / Ethylhexyl Methoxycinnamate ) associated with the antioxidants ferulic acid (FA ) and resveratrol ( RES ). To this, Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC), tools very important for the thermal analysis were used. The results showed that the mixture BMBM with FA had physical interaction confirmed by TG profile. In the mixture of the ingredients BMBM with RES , probably it had BMBM hydrophobic bonds between hydroxyl groups of the phenolic rings of resveratrol, indicated chemical interaction. The mixture EHMC with FA, indicated chemical interaction. In the mixture RES with EHMC , EHMC solubilized RES , indicating physical interaction. In this mixture , RES probably would be bioavailable that is facilitate its penetration and action on the skin. The results showed that by DSC and TG techniques, it is possible to predict the stability profile of ingredients and formulations which will reflect in its efficacy and safety as UV photoprotection.