Abstract
Prior research has established that testosterone is an important modulator of social decision-making. However, evidence on the relationship between basal testosterone levels, commonly measured in saliva or blood, and social behavior has been inconsistent due to methodological shortcomings. Additionally, it has been suggested that cortisol might moderate the association between basal testosterone and social behavior. The present study examined how individual differences in cumulative hair testosterone map onto social decision-making under consideration of a potential modulating role of hair cortisol in a large community sample of young adults (N = 1002). We observed a negative association between hair testosterone and trust behavior (odds ratio = 0.84) and a positive association with self-reported aggressive behavior (β = 0.08). The effects were small and became nonsignificant after controlling for key covariates of steroid hormones in hair (e.g. hair color, contraceptives, and use of psychoactive substances). Hair testosterone levels were not significantly associated with any other social behavior examined, and no modulating effects of hair cortisol were found. Overall, these findings provide no evidence for a role of basal testosterone hair concentrations in human social decision-making and do not indicate that hair cortisol moderates hair testosterone's effects on social behavior.