Fifteen-month-old infants' cortisol levels decrease after a 30-min-warm-up procedure.

Stress-induction procedures designed to increase cortisol levels in infants have been ineffective in many studies. One reason might be that infants did not have sufficient time to settle into the laboratory environment prior to the start of the stress induction, and thus already had high baseline levels of cortisol. In this study we investigate whether an extended warm-up period reduces infants' (N=22) cortisol levels. Fifteen-month-old infants' saliva cortisol was measured upon arrival at the laboratory. Then, they were allowed to play with their parent. After 30min, cortisol was measured again. There was a decrease in cortisol after 30min of free play. Our study suggests that infants' cortisol levels decrease when infants have the opportunity to acclimatize to the test environment. An extended warm-up phase prior to stress induction procedures might be necessary to reliably increase cortisol levels in infants.