Hormonal interactions might shape fairness toward friends and strangers in adolescents

A study in China found that older adolescents increasingly favor friends over strangers when deciding how to divide game tokens—reflecting shifts in both strategic and pure fairness decision-making. Testosterone levels were linked to differences in strategic fairness, but only when bedtime basal cortisol levels were also high. The paper was published in Psychoneuroendocrinology.

Fairness refers to treating others impartially, without favoritism or bias. Psychologists often distinguish between pure fairness—when individuals act fairly because they believe it is morally right, even at personal cost—and strategic fairness, which is motivated by a desire to secure reciprocity, maintain social reputation, or gain peer approval.

In early childhood, fairness is often egocentric and focused on equal division of resources. But during adolescence, fairness becomes more context-sensitive, shaped by a growing capacity for abstract reasoning and perspective-taking. Adolescents begin to weigh both moral obligation and social strategy when making decisions, particularly in peer interactions where social status and group belonging are highly valued.

Study author Rui Su and her colleagues sought to examine how adolescents’ fairness behaviors evolve with age and differ between sexes. They also investigated how cortisol and testosterone—two hormones linked to stress and social behavior—interact to shape fairness in decisions involving close peers versus strangers.

Cortisol is the primary stress hormone, involved in the body’s metabolic and threat-response systems. Testosterone, a sex hormone, is associated with dominance, competition, and status-seeking. The dual-hormone hypothesis suggests that testosterone’s behavioral effects are strongest when cortisol levels are low, but are diminished—or sometimes reversed—when cortisol is high.

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The study included 380 adolescents between the ages of 10 and 17 (average age: 14.6 years), all typically developing with no history of neurological or psychiatric illness. Participants were not taking medications during the study period. About 63% were male.

Participants completed two behavioral tasks:

• Ultimatum Game (UG): Each participant decided how to divide 10 tokens between themselves and a responder, who could accept or reject the offer. If rejected, neither party received any tokens. Each participant played this game twice—once with a friend and once with a stranger. This setup measured strategic fairness, since rejection was a possibility.
• Dictator Game (DG): Again, participants divided 10 tokens between themselves and another person, but this time the receiver had no choice but to accept the allocation. This version assessed pure fairness, as it removed any strategic considerations.

The researchers considered the difference in token allocation to friends versus strangers as an indicator of the role of social distance in fairness behavior.

To assess hormonal levels, participants collected five saliva samples across a 12-hour period, including one before bedtime and four in the morning after waking. This allowed researchers to measure both bedtime basal cortisol and the cortisol awakening response (CAR)—a sharp increase in cortisol that typically occurs about 30 minutes after waking. Testosterone was also measured from the bedtime sample.

The overall number of tokens allocated to friends or strangers was not significantly associated with age. However, as adolescents matured, they increasingly favored friends over strangers, particularly in the Ultimatum Game, where fairness decisions had strategic implications. This pattern was observed in both boys and girls.

Importantly, hormonal interactions played a role in strategic fairness, but not in pure fairness.

Adolescents with higher testosterone levels showed larger differences in how they treated friends versus strangers—but only if they also had high basal cortisol. Among these individuals, testosterone appeared to enhance parochial fairness in strategic contexts.

A similar interaction emerged with cortisol awakening response. In adolescents with low CAR, higher testosterone was associated with greater differentiation between friends and strangers in token allocation. In contrast, among those with high CAR, higher testosterone was associated with smaller differences, suggesting a broader willingness to treat strangers more fairly. These hormonal patterns were observed only in male adolescents.

“As adolescents mature, they increasingly consider social distance in both strategic and pure fairness decisions, favoring friends over strangers. High testosterone levels are positively associated with allocation differences in strategic fairness at high basal cortisol levels, but not at low levels. Furthermore, in male adolescents only, testosterone levels are positively correlated with allocation differences in strategic fairness at low CAR, but negatively correlated at high CAR,” the study authors concluded.

The study contributes to the scientific understanding of the effects cortisol and testosterone levels have on fairness decisions. However, it should be noted that the study involved participants dividing game tokens, items of low importance to them. Results might be different in situations where individuals make decisions on of high personal importance.

The paper, “Cortisol and testosterone jointly affect adolescent fairness,” was authored by Rui Su, Huagen Wang, Xiang Ma, Nan Sun, and Chao Liu.