Physical pain increases interpersonal trust in females.

Background: People behave and interact with others differently when experiencing physical pain. Pain has dramatic effects on one's emotional responses, cognitive functions and social interaction. However, little has been known about whether and how physical pain influences interpersonal trust in social interaction. In the present study, we examined the influence of physical pain on trusting behaviour.

Methods: A total of 112 healthy participants were recruited and assigned to physical pain condition (induced by Capsaicin) and control condition (with hand cream), respectively. Thirty minutes after pain induction, three decision-making tasks were conducted to measure behaviours in social interaction, including trust and trustworthiness (trust game), non-social risk-taking (risk game) and altruism (dictator game).

Results: Results showed that physical pain increased interpersonal trust among females, but not among males. Pain did not influence non-social risk-taking, altruism or trustworthiness, as evaluated by monetary transfers in those tasks. Moreover, the effect of physical pain on interpersonal trust was fully mediated by expectation of monetary profit.

Conclusions: These findings demonstrate an effect of pain on interpersonal trust and suggest a reciprocity mechanism that the effect may be driven by self-interest rather than altruistic motivation. The pain effect on trust was evident only in females, implying distinct pain coping strategies used by both genders.

Significance: The present work highlights the social component of pain and extends our understanding of mutual interactions between pain and social cognition.