title: Film thickness frequency distribution of different vehicles determines sunscreen efficacy.
abstract: Sun protection factor (SPF) frequently differs between sunscreens containing the same composition of ultraviolet (UV) filters that primarily define sunscreen efficacy. We tested the hypothesis that the thickness frequency distribution of the sunscreen film is also responsible for and can explain the divergence in the measured SPF. For this, we developed a method to measure film thickness from the difference of topography before and after application of of sunscreen on pig ear epidermal membrane. The influence of five vehicle formulations and of application pressure and spreading time on mean thickness ( ), to median ratio, and SPF in vitro was investigated. The vehicle had a significant impact, low vehicle viscosity resulting in a smaller , larger to median ratio, and lower SPF in vitro than high viscosity; continuous oil phase produced the largest and SPF values. A long spreading time reduced and SPF and increased application pressure reduced SPF. There was a positive correlation between and SPF in vitro, underlining the relevance of film thickness for interpreting UV protection differences of formulations with the same filter composition. This work demonstrated a strong influence of vehicle and application conditions on sunscreen efficacy arising from differences in film thickness distribution.
authors.affiliation: University of Applied Sciences and Arts Northwestern Switzerland, School of Life Sciences, Institute of Pharmaceutical Technology, Gründenstrasse 40, 4132 Muttenz/Basel, SwitzerlandbUniversity of Basel, Department of Pharmaceutical Sciences, Klingelbergst.
authors.forename: Myriam
authors.initials: M
authors.lastname: Sohn
authors.affiliation: University of Basel, Department of Pharmaceutical Sciences, Klingelbergstrasse 50, 4056 Basel, Switzerland.
authors.forename: Adeline
authors.initials: A
authors.lastname: Hêche
authors.affiliation: BASF GmbH, Köchlinstrasse 1, 79639 Grenzach-Whylen, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Herzog
authors.affiliation: University of Applied Sciences and Arts Northwestern Switzerland, School of Life Sciences, Institute of Pharmaceutical Technology, Gründenstrasse 40, 4132 Muttenz/Basel, SwitzerlandbUniversity of Basel, Department of Pharmaceutical Sciences, Klingelbergst.
authors.forename: Georgios
authors.initials: G
authors.lastname: Imanidis
mesh_terms: D000818:Animals; D004817:Epidermis / Q000502:physiology; D014677:Pharmaceutical Vehicles / Q000737:chemistry*; D059405:Sun Protection Factor / Q000379:methods*; D013473:Sunscreening Agents / Q000737:chemistry*; D013552:Swine; D014466:Ultraviolet Rays; D014783:Viscosity
chemical_list: D014677:Pharmaceutical Vehicles; D013473:Sunscreening Agents