Influence of Titanium Dioxide Particle Size on the Photostability of the Chemical UV-Filters Butyl Methoxy Dibenzoylmethane and Octocrylene in a Microemulsion

Jutta Kockler,Sherryl Robertson,Michael Oelgemöller,Beverley Glass

doi:10.3390/cosmetics1020128

Abstract

Sunscreen products often contain combinations of ultraviolet (UV)-filters in order to achieve broad spectrum protection from exposure to sunlight. The inclusion of both chemical and physical UV-filters in these products, however, increases the possibility for both photolytic and photocatalytic reactions to occur. This study investigated the effect of titanium dioxide (TiO2) particle size on the photostability of the chemical UV-filters butyl methoxy dibenzoylmethane (BMDM) and octocrylene (OC) formulated in a microemulsion. The International Conference on Harmonisation (ICH) Guideline Q1B for photostability testing of new active substances and medicinal products was applied. BMDM and OC in the microemulsion were irradiated with simulated sunlight in the presence of nano- (<25 nm) and micro-TiO2 (~0.6 μm) and their concentrations determined using a validated high performance liquid chromatography (HPLC) method. For the combination of BMDM and OC, the photodegradation for BMDM was found to be 12% higher in the presence of nano-TiO2 as compared to that of the micro-TiO2. This enhanced photodegradation is attributed to the larger surface area of the nano-TiO2 and the increased generation of reactive oxygen species (ROS). Because of these findings, sunscreen products containing chemical UV-filters and nano-TiO2 should be regarded with caution, due to the potential loss of photoprotection.

Highlights

Sunscreen products often contain a combination of ultraviolet (UV)-filters to achieve broad spectrum UV-protection
All irradiations were performed on the microemulsion, representing a typical formulation used for the topical application of sunscreens
This study has demonstrated that nano-TiO2 induces photodegradation of the UV-filters butyl methoxy dibenzoylmethane (BMDM) and OC

Summary

Introduction

Sunscreen products often contain a combination of ultraviolet (UV)-filters to achieve broad spectrum UV-protection. TiO2 is a physical filter offering protection from both UVB- (290–320 nm) and UVA I (320–340 nm)-light. UV-filter, protecting from UVA I- and UVA II (340–400 nm)-light, while octocrylene (OC, Figure 1). Photostability of UV-filters is essential to ensure protection from dangerous health effects such as skin cancer or immunosuppression, caused by excessive exposure to UV-light [1]. TiO2 is photostable, some chemical UV-filters such as BMDM are susceptible to photodegradation on UV-irradiation [2]. Photodegradation results in a loss of UV-protection, since most photodegradants show UV-absorption at lower wavelengths than their parent compounds. These photodegradants may cause allergic skin reactions and other toxic effects. It was shown that exposure of octyl methoxycinnamate to UV-light increased the toxicity to mouse cells [3]

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Conclusion