title: Calculation of the sun protection factor of sunscreens with different vehicles using measured film thickness distribution - Comparison with the SPF in vitro.
abstract: The sun protection factor (SPF) depends on UV filter composition, and amount and type of vehicle of the applied sunscreen. In an earlier work, we showed that the vehicle affected the average thickness of sunscreen film that is formed upon application to a skin substrate and that film thickness correlated significantly with SPF in vitro. In the present study, we quantitatively assess the role for sunscreen efficacy of the complete film thickness frequency distribution of sunscreen measured with an oil-in-water cream, an oil-in-water spray, a gel, a water-in-oil, and an alcoholic spray formulation. A computational method is employed to determine SPF in silico from calculated UV transmittance based on experimental film thickness and thickness distribution, and concentration and spectral properties of the UV filters. The investigated formulations exhibited different SPFs in vitro and different film thickness distributions especially in the small thickness range. We found a very good agreement between SPF in silico and SPF in vitro for all sunscreens. This result establishes the relationship between sun protection and the film thickness distribution actually formed by the applied sunscreen and demonstrates that variation in SPF between formulations is primarily due to their film forming properties. It also opens the possibility to integrate the influence of vehicle into tools for in silico prediction of the performance of sunscreen formulations. For this, the use of the Gamma distribution was found to be appropriate for describing film thickness distribution.
authors.affiliation: University of Applied Sciences and Arts Northwestern Switzerland, School of Life Sciences, Muttenz/Basel, Switzerland; University of Basel, Department of Pharmaceutical Sciences, Basel, Switzerland.
authors.forename: Myriam
authors.initials: M
authors.lastname: Sohn
authors.affiliation: BASF Grenzach GmbH, Grenzach-Whylen, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Herzog
authors.affiliation: BASF Personal Care Nutrition GmbH, Monheim, Germany.
authors.forename: Uli
authors.initials: U
authors.lastname: Osterwalder
authors.affiliation: University of Applied Sciences and Arts Northwestern Switzerland, School of Life Sciences, Muttenz/Basel, Switzerland; University of Basel, Department of Pharmaceutical Sciences, Basel, Switzerland. Electronic address: georgios.imanidis@fhnw.ch.
authors.forename: Georgios
authors.initials: G
authors.lastname: Imanidis
mesh_terms: D002626:Chemistry, Pharmaceutical; D066298:In Vitro Techniques; D014677:Pharmaceutical Vehicles; D013473:Sunscreening Agents; D014466:Ultraviolet Rays
chemical_list: D014677:Pharmaceutical Vehicles; D013473:Sunscreening Agents
keywords: Convolution; Film thickness frequency distribution; Formulation; SPF in vitro; Sun protection factor; Sunscreen; Vehicle