CONSTANZE STIEFEL*, WOLFGANG SCHWACK
*Corresponding author
Institute of Food Chemistry, University of Hohenheim, Garbenstrasse 28, 70599 Stuttgart, Germany

Abstract

Due to the increasing public awareness of the harmful effects of an excessive sun exposure, the use of sunscreens continuously increased during the last decades. Although the photoprotective effect of these products is undisputed, they also can cause some undesirable skin reactions. Especially UV filters are seen as cosmetic ingredients that typically can induce contact dermatitis or photocontact dermatitis upon UV exposure. A penetration through the skin and the ability to form protein adducts (haptenation) are seen as key elements of the sensitization process. Although widely used for decades, the underlying mechanism of a possible (photo) sensitization due to UV filter usage and the reactivity of these active substances towards skin components were not in the focus of scientific publications for a long time. As UV filter stability is crucial for the efficiency and safety of sun protection products, this review will give an overview of recent publications concerning the reactivity of cosmetic UV filters towards amines, peptides, different protein models and skin proteins.

INTRODUCTION

A majority of the consumers are well aware of the negative effects that excessive sun exposure can have on human skin. Accordingly, the demand for effective sun protection products has risen steadily over the last decades. Nowadays, UV filters are not only used in sunscreens but are also important ingredients of various personal care products for daily use. To show effective protection ability and ensure a safe usage, cosmetic UV filters need to be photostable and chemically inert (1). However, beside the already known photodegradation processes, many of the UV filters approved in the European Union (EU) provide reactive carbonyl groups, for which a reaction towards nucleophilic side chains of skin proteins is conceivable. Such reactions are not covered by recent in vitro methods used to examine sunscreen performance. However, they may have a negative impact on the tolerability of the UV filters and are therefore subject of the current review.
For a long time, guinea pig methods and the murine local lymph node assay (LLNA) were the preferred testing methods to predict the sensitization potential of a substance (2). However, due to et ...