Background: Skin cancer is the most prevalent but also most preventable cancer in Australia. Despite Australia's long running public health campaigns, young Australian adults continue to report high levels of ultraviolet radiation (UVR) exposure and frequent sunburns. Young people are now increasingly turning away from traditional media such as newspapers and TV favouring online streaming, which is challenging the healthcare sector to develop new ways to reach this group with targeted, personalised health promotion messages. Advances in technology have enabled delivery of time-and context-relevant health interventions. Objectives: The primary aim of this randomised controlled trial (RCT) was to test the effect of ultraviolet radiation feedback from a smartphone application (app) APP or a UVR dosimeter feedback device on sun protection habits, sun exposure behaviours, sunburn, and physical activity levels in young adults. Methods: Young adults aged 18-35 years (n=124) were recruited from Queensland, Australia