Losing face? Facial activity during evaluative stress is characterized by rigidity, tension and unpredictability.

Psychosocial stress detection via cost-effective means could prove a useful tool in the diagnosis of long-term stress experience and subsequent prevention of stress-related health disorders. Facial expressions are both part of and a relay for complex affective states, such as acute stress. In the current post-hoc study we investigated differences in facial activity between participants under acute psychosocial stress and in a stress-free control task. N = 126 adults either completed the Trier Social Stress Test (TSST) or a stress-free placebo TSST while being video recorded. Stress group participants also provided multiple samples of salivary cortisol, heart rate, heart rate variability and subjective stress. Facial activity was indexed via action unit (AU) activity on a frame-by-frame basis. We found that stress group participants showed significantly less facial activity across AU04 (brow lowerer), AU06 (cheek raiser), AU07 (eyelid tightener) and AU12 (lip corner puller) during the talk but not during the math block of the TSST. These group differences were not further explained by participant sex. These findings were corroborated by dynamic structural equation modeling of facial activity. Physiological and psychological stress reactivity, however, was not revealed to covary with facial behavior during evaluative stress. In conclusion, this study is another step towards stress detection via easy-to-implement and cost-effective means.