Condom use is known to decrease as relationships evolve from new/casual to regular [MaDeArHo00]. Explanations for less condom use in the latter case emphasize relationship longevity as impelling higher intimacy and trust levels between partners. However, condom use rates in casual relationships are below 50% and recent studies point to longer casual relationships, involving well-known partners, with a variety of emotional manifestations and sexual intimacy. Could this low usage be better understood if casual relationships were longer relationships? How and under what conditions does a multitude of experiences, varying in temporal, emotional, and acquaintance dimensions affect no condom use in casual relationships? Answers to these questions open a new perspective of sexual behavior analysis that has yet to be accomplished. The crucial issue is that there are more similarities than differences in relational characteristics among some types of casual and regular relationships that hamper condom use. Studies have been conducted on the socio-emotional implications of the hybrid nature of casual relationships, but not their impact on sexual protection.

The main goal of CRUSh (Casual Relationships Upshots for Sexual Protection) is to conduct an in-depth analysis of the diversity of casual relationships in emerging adults (18-29 years), their relationship characteristics and condom use within a script theory framework. This study contributes to: elucidating the small gap in condom use between casual and regular relationships; innovating by suggesting that the similarity between the characteristics of casual relationships and regular relationships may explain such similar levels of condom use and; script theory, by studying the role of context and individual characteristics for script tracks. The long-term aim is to scientifically underpin interventions to increase the proportion of individuals who report using condoms in occasional sexual relationships, as advocated by the National Program for Prevention and Control of HIV/Aids.

Research has focused mainly on distinguishing types of casual relationships, axes for their characterization, gender differences, predictors, and associations with mental health. Given this exploratory and correlational stage in research, comparisons to determine the differences in condom use between casual relationships and the similarities with regular relationships, in qualitative and quantitative studies, with longitudinal and experimental designs, are yet to be made. Such is also the case with the study of condom use mediation in the different casual experiences, and more fine grained observational studies of condom use in transitions between relational statuses. The strategy to achieve the proposed aims is organized in eleven studies for which the complementary expertise in sexual behavior and research methods of the team is an asset.