Introduction: Sun exposure has harmful short- and long-term effects, particularly on the eyes and skin. The most serious consequence, melanoma, is a form of skin cancer that is on the rise in most European countries. Despite prevention campaigns, the French population continues to overexpose itself to the sun and to use insufficient protection. In the summer, tourists along the Mediterranean coast are a particularly at-risk population due to high ultraviolet (UV) radiation and overexposure behaviors driven by the desire to tan. According to the literature, appearance-based interventions (ABIs) highlighting skin photoaging show promise for improving behaviors, but methodological limitations are noted. The objectives of this thesis were 1) to identify the determinants, particularly social and psychosocial ones, of sun protection and exposure to natural UV radiation among French summer tourists on the Mediterranean coast of Occitanie; 2) to evaluate and compare the effectiveness of an AP intervention and a health-based (HB) intervention on their sun protection behaviors. Methods: During the summer of 2019, a cluster-randomized crossover trial was conducted among French tourists aged 12 to 55 staying at eight campsites along the Occitanie coast. Participants were divided into three groups: control, HB intervention (information on health effects, phototype calculation), or AB intervention (information on photoaging, UV photography). These interventions drew on mechanisms from the Theory of Planned Behavior and the Transtheoretical Model. The intervention allocation varied each week at each campground. Data collected face-to-face via questionnaires and skin color measurements were gathered immediately before (T0) and 4 days after the interventions (T1). A long-term follow-up was conducted in October 2020 (T2) using an online questionnaire. Results: At T0, 1,355 campers were included, of whom 95% participated in the follow-up at T1 and 44% at T2. Tourists who intentionally exposed themselves for tanning purposes were more often aged 15–24, female, of a less sensitive phototype, and had a positive attitude toward tanning and sun exposure. The tourists who used the least protection were the youngest, had a less sensitive skin type, lower educational attainment, lower theoretical knowledge of sun protection, a favorable attitude toward tanning, a social circle that encouraged them less to protect themselves (social norm), and who found it difficult to protect themselves during their stay (perceived control). The association between sun protection and educational level was partially mediated by the level of theoretical knowledge, and to a lesser extent, by misconceptions and attitudes toward tanning. Regarding the effectiveness of the interventions, both interventions improved protective behaviors in the short term, but only the appearance-based intervention improved them in the long term and reduced intentional exposure in both the short and long term. More educated individuals appeared to be more responsive to the HB intervention, while those with a high school diploma were more responsive to the AB intervention. Conclusion: Our results highlight at-risk subpopulations among coastal tourists and provide original evidence of the effect of individual interventions aimed at modifying sun protection behaviors in this population. They underscore the relevance of appearance-based messages to complement health messages in this context, particularly among certain subpopulations with low to intermediate levels of education, and the need to improve knowledge to reduce social inequalities in sun protection.