Cortisol and testosterone jointly affect adolescent fairness.

Fairness is crucial in social interactions, shaping relationships and fostering cooperation, especially during adolescence. The developmental period, characterized by significant hormonal changes such as fluctuations in cortisol and testosterone levels, is pivotal for physiological and behavioral maturation. Despite the importance of the hormones, studies investigating their interaction effects on fairness within adolescent populations remain limited. The current study explored adolescent fairness development and how cortisol (bedtime basal cortisol and cortisol awakening response, CAR) and testosterone interacted in strategic and pure fairness towards friends and strangers, using adapted versions of the Ultimatum Game (UG) and Dictator Game (DG), separately, in 381 typically developing adolescents (37 % female, Mage = 14.6 years, SDage = 1.95). As adolescents matured, they increasingly favored friends over strangers in both strategic and pure fairness decision-making. Testosterone was positively associated with allocation differences in strategic fairness only at high bedtime basal cortisol levels. Additionally, testosterone was positively correlated with allocation differences in strategic fairness at low CAR levels but negatively at high CAR levels. This hormonal pattern was observed only in male adolescents. These findings underscore sex-specific patterns in dual-hormonal influences on adolescent fairness decisions and highlight the role of physiological hormones in the development of moral values in distinct ways for males and females.