Double effect: The oxytocin known as the “cuddle hormone” not only strengthens our bonds with familiar people – it is also active in rivalries between groups, as a field study shows. On the one hand, oxytocin promotes cohesion and cooperation within one’s own group. But it also increases distrust and vigilance against potential threats from adversaries. The cuddle hormone does not make you more social per se, but rather helps you adapt to social circumstances, as the researchers explain.
The messenger oxytocin is considered the “cuddle hormone”: It is released whenever we interact with familiar or loved ones. This helps us feel relaxed and build social bonds and trust more easily. For example, oxytocin strengthens the bond between mother and child or between partners in a relationship. At the same time, the hormone reduces stress levels and can even relieve pain and promote wound healing.
But the cuddle hormone has a downside: Studies show that it is also released more frequently in conflicts, rivalries between groups and even domestic violence. In such situations, oxytocin seems to make people more hostile and aggressive. “This seemingly paradoxical duality becomes clearer when we know that oxytocin does not make people prosocial or antisocial per se, but rather helps with adaptation to the social situation,” explain Charlotte Debras from the University of Zurich and her colleagues.
Football games as a test case
The researchers examined what this means in practice with the Tsimane indigenous people in the Bolivian Amazon region. These hunter-gatherers live together in small groups, usually consisting of a few families. Within these communities, families cooperate in daily chores and caring for children, but at the same time there is also competition for resources and social status, as the team explains.
Tsimane football games play an important role in reputation and social status in the group. The men from one community compete in such matches several times a week; on Sundays, football games take place between teams from neighboring communities. Women also take part in the games, but do so less frequently. “Such football games are described as emotionally very intense and characterized by strong rivalry,” report Debras and her team.
They examined how oxytocin levels in the blood of 90 Tsimane changed during football games within their own group, during games against neighbors and during games against non-Tsimane.
Significant increase in oxytocin
The analyzes showed: During and after football games, the men’s oxytocin levels rose significantly – but not always to the same extent. “The men showed the greatest increase in oxytocin in the matches within their community and in games against non-Tsimane,” the researchers report. In contrast, the release of the “cuddle hormone” was significantly lower during football games against neighboring groups. “This suggests that oxytocin reacts sensitively to the social importance of the opponent – both with familiar rivals and with clearly defined out-groups,” says senior author Adrian Jaeggi from the University of Zurich.
At the same time, the results confirm that the cuddle hormone plays a role not only in relationships between individuals, but also in groups. “Previous studies have shown that administering oxytocin in the form of a nasal spray can promote group-oriented behavior,” says Debras.
Internal cooperation, external defense
But why is the cuddle hormone released more during competition? According to Debras and her colleagues, these results fit well with the dual role of oxytocin: “In the context of a conflict between groups, the increase in oxytocin can, on the one hand, help to strengthen cooperation and trust within the own group and improve synchronous action,” explains the team. During a football game, this ensures that the team works together smoothly.
On the other hand, oxytocin also increases alertness and aggression towards the opposing group: “It improves the perception of potentially threatening signals from this group,” write Debras and her colleagues. “This function is crucial in group conflicts in order to distinguish allies from enemies, to recognize their intentions and to be able to react quickly to threats – all of this requires the rapid and effective reading of the social situation.” Oxytocin promotes these abilities.
Opponents and gender play a role
The differences depending on the opposing group can also be explained in this context: for men, football games within the community are closely linked to social prestige. Whoever wins shows dominance and superior skills and thus consolidates their status, as the team explains. In games against non-Tsimane, on the other hand, the clear “us against them” promotes cohesion within the team, while at the same time mistrust, competition and potential threats are greater. Both cause an increased release of oxytocin. Because neighboring groups are neither relevant to the status within one’s own group nor represent a potential threat, the hormonal response is weakest in these games.
Also interesting: There were clear gender differences among the Tsimane. Unlike men, women’s oxytocin did not increase when they took part in football games. Debras and her colleagues explain this on the one hand by the fact that women naturally have higher oxytocin levels and therefore no major increase is possible. On the other hand, Tsimane women achieve their social status through other mechanisms: “They compete through gossip, verbal attacks on reputation and social exclusion,” the researchers write.
Taken together, the results confirm that the cuddle hormone also plays an important role in competitive situations. “Cooperation can be a successful strategy in competition – and oxytocin seems to be central to this,” says Jaeggi. “Oxytocin has already been linked to group conflict in numerous animal species – from fish to chimpanzees. Our results suggest that similar mechanisms also operate in humans.”
Source: Charlotte Debras (University of Zurich) et al., Proceedings of the Royal Society B, 2026; doi: 10.1098/rspb.2026.0242