A double-blind, randomized assessment of the irritant potential of sunscreen chemical dilutions used in photopatch testing

Background: The maximum concentration of organic sunscreen filters in current usage that does not lead to irritant reactions when performing photopatch testing is not known. Such irritant reactions can be misinterpreted as positive photoallergic contact dermatitis reactions. Objective: To determine the frequency of irritant reactions to 19 organic sunscreen filters in current use. Patients/Methods: Ninety-four healthy volunteers were photopatch tested using the European consensus methodology to three different concentrations (2%, 5%, and 10%) of 19 organic sunscreen filters at the Photobiology Unit in Dundee, UK. Results: Of the 94 subjects recruited, 80 were analysed after withdrawals and exclusions. Of the 19 organic sunscreen filters studied, only 2 compounds led to irritant reactions in >= 5% subjects. Five per cent and 10% benzophenone-4 led to irritant reactions in four and six subjects, respectively. Five per cent methylene bis-benzotriazolyl tetramethylbutylphenol led to irritant reactions in six subjects, but unlike benzophenone-4, this was not in a dose-dependent fashion. Conclusions: When performing photopatch testing according to the European consensus methodology with these 19 organic sunscreen filters, a 10% concentration is suitable for all filters, except benzophenone-4, which should be tested at a concentration of 2%.