Does being a Stranger make it Difficult to Cooperate?

Competition and cooperation are two somewhat opposed strategies for interpersonal social interaction that help us to achieve both individual and shared goals. The main aim of this study was to explore which type of social interaction (cooperative or competitive) is more stressful in a face-to-face same-sex dyad in healthy young participants (n = 178), considering outcome obtained in these tasks (positive or negative) and sex as moderating variables, and performance of the task alone as a control condition. Salivary cortisol (Csal) was measured in one sample obtained before task and four obtained after the task (+0, +15, +30 and +45 minutes after). Anxiety-state was assessed before and immediately after the task. Participants who cooperated and obtained negative outcomes had higher Csal levels than those who worked alone with negative outcomes in all periods after the task (p = .008, η p 2 = .058 and p = .033, η p 2 = .031, respectively). Moreover, those who cooperated showed higher mean self-reported state anxiety levels than the rest of the participants (p = .013, η p 2 = .051 and p < .001, η p 2 = .530, respectively). Our study indicates that cooperation between strangers in face-to-face dyads is highly stressful, more so than competing or working alone. These results should be taken into account for understanding situations of social stress and can be generalized to situations in which subjects cooperate or must decide between cooperating and competing to attain a goal.