Morning‐to‐Afternoon Increases in Cortisol Concentrations for Infants and Toddlers at Child Care: Age Differences and Behavioral Correlates

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Abstract
This study examined salivary cortisol, a stress–sensitive hypothalamic‐pituitary‐adrenocortical (HPA) axis hormone in 20 infants (12 females; M age=10.8 months) and 35 toddlers (20 females; M age=29.7 months) in full‐day, center‐based child care. Samples were taken at approximately 10:00 a.m. and 4:00 p.m. at child care and at home. At child care, 35% of infants and 71% of toddlers showed a rise in cortisol across the day; at home, 71% of infants and 64% of toddlers showed decreases. Toddlers who played more with peers exhibited lower cortisol. Controlling age, teacher‐reported social fearfulness predicted higher afternoon cortisol and larger cortisol increases across the day at child care. This phenomenon may indicate context‐specific activation of the HPA axis early in life.