The unique contribution of blushing to the development of social anxiety disorder symptoms: results from a longitudinal study

Background:
Self-conscious emotional reactivity and its physiological marker—blushing, has been proposed to be an etiological mechanism of social anxiety disorder (SAD), but so far, untested in longitudinal designs. This study tested, for the first time, if self-conscious emotional reactivity (indexed as physiological blushing) contributes to the development of SAD symptoms over and above social behavioral inhibition (BI), which has been identified as the strongest predictor of SAD development in early childhood.
Methods:
One-hundred-fifteen children (45% boys) and their mothers and fathers participated at ages 2.5, 4.5, and 7.5 years. Social BI was observed at all time points in a Stranger-approach task and physiological blushing (blood volume, blood pulse amplitude, and temperature increases) was measured during a public performance (singing) and watching-back the performance at ages 4.5 and 7.5. Child early social anxiety was reported by both parents at 4.5 years and SAD symptoms were diagnosed by clinicians and reported by both parents at 7.5 years.
Results:
Higher social BI at 2.5 and 4.5 years predicted greater social anxiety at 4.5 years, which, in turn, predicted SAD symptoms at 7.5 years. Blushing (temperature increase) at 4.5 years predicted SAD symptoms at 7.5 years over and above the influence of social BI and early social anxiety.
Conclusions:
That blushing uniquely contributes to the development of SAD symptoms over and above social BI suggests two pathways to childhood SAD: one that entails early high social BI and an early onset of social anxiety symptoms, and the other that consists of heightened self-conscious emotional reactivity (i.e., blushing) in early childhood.