Stress contagion: physiological covariation between mothers and infants.

Emotions are not simply concepts that live privately in the mind, but rather affective states that emanate from the individual and may influence others. We explored affect contagion in the context of one of the closest dyadic units, mother and infant. We initially separated mothers and infants; randomly assigned the mothers to experience a stressful positive-evaluation task, a stressful negative-evaluation task, or a nonstressful control task; and then reunited the mothers and infants. Three notable findings were obtained: First, infants' physiological reactivity mirrored mothers' reactivity engendered by the stress manipulation. Second, infants whose mothers experienced social evaluation showed more avoidance toward strangers compared with infants whose mothers were in the control condition. Third, the negative-evaluation condition, compared with the other conditions, generated greater physiological covariation in the dyads, and this covariation increased over time. These findings suggest that mothers' stressful experiences are contagious to their infants and that members of close pairs, like mothers and infants, can reciprocally influence each other's dynamic physiological reactivity.