The present in vivo investigation using a total of 30 healthy adult volunteers with Fitzpatrick skin type II examines the persistent efficacy of sunscreens using liposomal suspensions as the vehicle. Based on the COLIPA guidelines, the protective effect of a single application of 4 different liposomal sunscreen formulations (sun protection factors, SPFs: 50+, 30,25 and 15) against sunburn at the recommended amount of 2 mg/cm(2) was determined after exposure of the skin to plain water and salt water and after profuse perspiration. Under the influence of plain water, salt water and sweating, the SPF values of sunscreen 1 (labeled SPF of 50+) were reduced only marginally to 97, 96 and 99%, respectively, those of sunscreen 2 (labeled SPF of 30) to 97, 96 and 99%, respectively, those of sunscreen 3 (labeled SPE of 25) to 90, 83 and 91%, respectively, and those of sunscreen 4 (labeled SPF of 15) to 96, 96 and 95%, respectively. This set of data shows that despite plain water and salt water immersion or profuse sweating, the liposomal sunscreen formulation may deliver a long-lasting protective effect in everyday situations encountered by outdoor workers or during leisure activities. Copyright (C) 2010 S. Karger AG, Basel