Studies of facial responses during experimental and clinical pain have revealed a surprising phenomenon, namely, that a considerable number of individuals respond with a smile. So far, it is not known why smiling occurs during pain. It is possible that the “smile of pain” is socially motivated (e.g., reinforcing social bonds while undergoing an unpleasant experience). The present studies were conducted in an attempt to address the role of social motives in smiling during pain. In two studies, we varied the quantitative (level of sociality) and qualitative (properties of the relationship between interactants) components of the situations in which participants received painful stimulation. Participants’ faces were video-recorded and the occurrence of smiling was assessed. The occurrence of smiling differed depending on stimulus intensity and the properties of the relationship between interactants. Smiling occurred more often during the painful compared to nonpainful stimulation. Whereas the presence of a stranger (experimenter) reduced the smiling behavior, the presence of an intimate other increased it. Slight variations in the level of sociality, however, had no effect on the degree of smiling. Social motives possibly aimed at strengthening social bonds and thus ensuring social support appear to underlie smiling during pain. 1. Introduction There is now a substantial body of literature showing that people in pain evince a number of specific facial movements [1], with a set of at least three or four distinct facial actions showing a close linkage to pain [2, 3]. However, this core set of pain-indicative facial actions is often blended with a range of seemingly incongruent expressions. Among the most frequently reported—in experimental as well as clinical studies [2, 3]—is the action of the zygomatic major muscle, which pulls the lip corners upward obliquely [4]. This finding appears surprising because the action of the zygomatic major is better known as the principal movement in the most common human facial expression—the smile [5, 6]. Given that facial expressions occurring during pain have been shown to not only impact social interactions (by eliciting solicitous behaviors and empathic responses in observers) but also impact pain diagnostic and pain treatment we believe it is important to investigate this seemingly incongruent facial expression, namely, “smiling during pain.” Although one might initially associate a smile with happiness or at least with a marker of a positive, non-painful affective state, it has been shown that there are different
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