The development of the cortisol response to dyadic stressors in Black and White infants.

Acute reactivity of the stress hormone cortisol is reflective of early adversity and stress exposure, with some studies finding that the impact of adversity on the stress response differs by race. The objectives of the current study were to characterize cortisol reactivity to two dyadically based stress paradigms across the first year of life, to examine cortisol reactivity within Black and White infants, and to assess the impact of correlates of racial inequity including socioeconomic status, experiences of discrimination, and urban life stressors, as well as the buffering by racial socialization on cortisol patterns. Salivary cortisol reactivity was assessed at 4 months of age during the Still Face paradigm (N = 207) and at 12 months of age across the Strange Situation procedure (N = 129). Infants demonstrated the steepest recovery after the Still Face paradigm and steepest reactivity to the Strange Situation procedure. Race differences in cortisol were not present at 4 months but emerged at 12 months of age, with Black infants having higher cortisol. Experiences of discrimination contributed to cortisol differences within Black infants, suggesting that racial discrimination is already "under the skin" by 1 year of age. These findings suggest that race-related differences in hypothalamic-pituitary-adrenal reactivity are present in infancy, and that the first year of life is a crucial time period during which interventions and prevention efforts for maternal-infant dyads are most likely able to shape hypothalamic-pituitary-adrenal reactivity thereby mitigating health disparities early across the life course.