Photostability of Octyl‐P‐Methoxy Cinnamate in O/W Emulsions and in SLNs Vehicled in the Emulsions

The photochemical degradation of the sunscreen p‐octyl‐methoxy‐cinnamate (OMC) was studied in different media: Finsolv TN (a fluid ester), O/W emulsion and gel‐emulsion. OMC photolysis was performed using an UVB lamp and the degradation kinetic was studied in presence of various initial concentration of the active. The study was performed comparing the naked to the SLNs form of the active and the experiments were monitored with HPLC/UV‐VIS apparatus. Results suggest that lower is the concentration of the UVB sunscreen in the formulations more pronounced is its photodegradation rate. In all the cases the inglobation of OMC into SLNs leads to an over additive UV‐blocking effect.